The Goldquartz Veins of Nevada City and Grass Valley Districts, California

Waldemar Lindgren · 1896 · Historical

Chaptkh X.— f'huiiKi H iu tbu rmka due to flMure and vein formation 14S ClIArTKW IV. — Tbf Igneong rorkw of the weripa — Contlnniwl. Page. CAin Ki< V.

This 1896 document, The Goldquartz Veins of Nevada City and Grass Valley Districts, California, is preserved in the Mountain Man Mining Library for research and reference. Original source: archive.org.

z veins of Nevada City and Grass Valley Districts, California

dgre

H.W.Turner.

Library.

Btquest of Henry W. Turner

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H. W. Turner.

Library.

DEPARTMENT OF THE TTJTEBIOB-U, B. QEOLOOICAL 80RVET <'IIAi:i.>M l. WAIX'OTT, IJIIIECTOK

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SB AIIA HTV AMI CKASS VAI.LEV IHSTIiHTS. CALlFllllMA

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I'Aiii' II - <;i;or.<M;Y and iivituncit vi'ii v

THK {;uLl)-Ql AKTZ VEINS OF NEVADA ( ITV AND GRASS VALLEY DISTRICTS, CALIFORNIA.

WAJDKMAJf iXr JU:K.

Co Nth Nts.

i'HArrtii 1 — 13

Fii'M mit ali'l .U ftliim ilKllIfHtn 13

poaition 13

I 'r!iiu;ia 14

History 17

velopiiiciit of ininipi: iiitTeta 18

CJiiart/ mininp 19

of niiiiiiitf atul milling '£t

Hvlr-'i'lHiiiiiiiHg 22

llrift miuinit - '£t

Quartz miiiini; T2

Milling 23

I.IWtH of golll 24

I Ik-rv.uini'' 25

PrniliU'tion 22k

Tin- Ix'il-roi'k Hcrii-H 2&

Chaitku hi. — The iguruuB roi'ka of tli btl-rock eriw 35

rirmuMlinriti. - - - 3u.

Kxii iir ami I li.inii Ipr iiT wiirlarw iUt

Microix opical ile-Hrription 3G

CliciuR-al 38

Helatioii to Murroiiiidiiig rock 38

ffcrif-H AH

mul grnnoilioritt northwagt of Nevada City mine iO

iliki'M lu ur liuliaii Klut i il

Oraif Vullov are* -11

Katt. nt ftmi rliarm tf r of warfare- H

Ho4:k dem-ription II

42

Kelittion to aurroundiiig rofkn 44

Aniite 44

Onmit'-porphyry 45

Dprinilinn , ilk

Occ'urttmca and docription 45

CiiAPTKR III. — The igngo"'* roch of the bed-rock aerial— Continaad. Taee.

Jo

Orit 1**iiiri il i Ari t A-nvfnimni Ia anuk

PlAiiMiitit. l'*1&t. ilinritA iinn

Df'Hcriptioii of

Til

fi-:it ii ri H

Rl

ni

M

M

tiTKU IV. — The i({ii<-on8 rocks of the iwrifw (i'ontinnl) . ...

,W

Hm

5K

fiO

Wi'athjTiiijj

f liwiirriMii'H -

M

Ufliitioii to otlMrrookH

J

Contents.

ClIArTKW IV. — Tbf Igneong rorkw of the weripa — Contlnniwl. Page.

Tlic >liabao uud ari-n gtoini — 'ontiiiiiecl.

The diabawr ilik'H in thf. Maryland Berpetitine 65

Exteut , fifi

DeHcriptimi of nx kH . . 66

The niigitf-ayciiite South Wolf Creek 68

Thw dinlmne and itorphyrito dikea in the ('alavi'ran formation of (iran

Vail, y 6t>

North Star <li!il>:tae and area 70

l'-M''iit 70

IfplMtiDii <i. iitlmrriipkw

Onborne Hill <iinl>.iM-, iioriibvriti-. and nra 73

Dewcriptiiiu of rockii 73

Wt-athvring 74

Rltinii tn iithnrr. kii 21

Orli-atK Miiarty imritliyrite dikea 74

The uiiiiihiliolili' 75

I Zi2

Indian Flat anipbibolite area 76

EztUli . - . Zfi

Di'Hcrlptiou "f 76

nn-a rhUtu'f imriilivrilu-tiri rciu (in pull aiiipliiliolite i , 78

LxlLUi ffl

of rock 7X

Weatherinic 78

CAin Ki< V. — 'I In- B<-dimi'utarv rock "f the licd-rock m-riea 78

i t<'iu'i :il liial iirrM 7t>

n.'liiiiiiim , 22

l-'Mlyral I.ivnn ir..<t ,

Ko<'k deaeription 80

Weatht'ripg 82

Contnot innt;nnorphiitro 82

rttiindii Hill ui-i.u : 83

Nevada City area 84

Kxtent and funeral oharartcr tM

I'fstTiptitiii iiI'kx Us 84

li'rlMtii.ri In other lucks 8S

Gnum Vallry area 86

General dfttcription 86

The fel'Upatliii' iiyrrhotity yeiwa 87

('ontiirt-iin'taiiiurpliir nx'kii 87

Qnarty.-tourmalint rock 88

Nnrth Star arpa 88

Maripona formation 88

CliAi'TF.n M<-taiiirpliic ttroceaaea 90

Ki'quark-- 'iii iin l.imiiriilii.sm 90

Alteration of f-ldgpan> iu the rueke by hydro-iiiemli-al proi-eeaes 88

6 Contents.

ClIAITKK VI. — Mi'taiiinrpliiiprdCfiiKes — ('ominiifl. Pmb.

( U i-iiri ITU e niiil rni iii.tii'iii <i)' hoii Ml liili iili ill ttiiim kn 03

fwntiirwM <j3

Prodncto of mngniatic cunaolidatiim &4

Piwlncto of rontart nietanioriihim 9i

PrwlucU of ilvnnnio-cheiuicul mrtnniornhiiui M

taof cominoii hvdro-m-tamonibtiini

PrtMliicttt of liylro-thfruil prtK-foiw* lU

Weatlieriiiir itS

Tbi' nuriffrniin iiravelH OT

Klivnlili. lllflll 98

Aii.l.'wil i.- tii!l-< i19

Alliiviiiiii li_L

Ki'niiiiiiuf liintorv of tlir nerve* 1(>2

llitor.vof the Bupgrjaceiit 106

Till' gap ill tin' it'iiinl 105

TliH I 111- In il nil k Miirl'a-o IPS

Tln' Ulll I I I'l <ius m livrl- - . - - . - - .

Till. % ;m ir lliiw H , . LID

f'iiAiT>:K IX-— Tilt, ori'g 112

(eiipriil fnatiirea of tlir t;"ll-i"a>'t8 veina 112

Milientlottv of tlie vfiim 114

Ganguo iiiineraU 114

Opal and fhalradonite 114

Lakilfi ill

Magticaito IIJ

Arw iniiiwralM Uij

Aliaitc LZ

Tetradviuite 17

Pyrit. 117

Pvrrliotiti' 118

Chnlropyriti- 118

UakniL. m

PyinrKxrite. iiluitiile. iinil iiTKeiitilc 119

C'iiiii ilinr Llll

Proluct of Mirlai I- iln iiiiii'i'-ili'iii 11'.'

MineraU nut connected willi tliu quart/ veitia VM

CopptT ll'O

l-'O

liiimiJ 12U

Contents. 7

Chaitkb IX. — Tha orea — Contlnnwl. Pngw.

Slincralo;rv of the vaim — Continued.

AliiHTuls not witli ttiaTXT. Vffinn — ( ontinii(*<1.

Fmlnrnl Loan inin

VIniintjiinmT tiilnn . . .

Tim nrmi

VJi

HAnfral rharmrtr.

1_U

The Bold

Character

1 >ilVi riiii; HtniPtun-g 128

.Mil rPHi oiiic fi'utiirt'is 130

Chaptkh X.— f'huiiKi H iu tbu rmka due to flMure and vein formation 14S

r:i-li>-l':>l li,:lTrir.-s

fhoiiiinnl nil. r:il i.iii

lifi

14G

field aiitl ftilviT of till" iiltiTfd Willi rofkH

1S7

ClIAITKl: — fill sliui'liire mul hlnmls 158

Strin liiro of tlio v-ina liS

<;-iii i.il r. :Hiir.-ii - - 13a

Ftiriii iif till-whiKitw mo

Oiieation of nerniniience in dcnth Itil

Croiw-rnttiiig KB

CHAlTKit XII. -Till' lis,nirf syntfinit Iftl

Ttn' witli li yeiH Tiil eixt-wc'Ht (strike IfH

Willow N'iilU-y Kro'ip 161

Xortli Star ;;iom> 164

St. IvOiiiH ttroun 164

Idalio-OrliMiiH t;riin 165

The veins witl> ui'iuTal imrtli-Noiith ntrikc Ife'

I'rovidciii uroiip

Contents.

Charartcr of 132

Oritjiii "f tilliiietala imtl gaiittng 174

Rjir. r riii ill tlHTocka . 17*

Soluliility <ii' tlm minemlii 176

Kelatioii of increacl prcwiiire atul t;minTture 177

SyntheeiH of gaugiie mineralg 178

Solubility of Kol.l 179

Suliiliililv ol "iilpli nil' nuiKrals 179

Effecto of increaacii and tomperature 180

Syntbetis of tho snlphnleg 181

of 182

Banner Hill .listrirt Ufi

Vcina of the I fn-ok Buin apd Willow Valley 185

Pwh'rnl 1 ii in vpiii ISfi

CoiiHlilutinii iiiid I.i vaiit <'iiiini- 1S7

Lecounitou - 187

Hcllt;fountttin v. in ISS

Never Sweat and Omega veiiw 188

Montana vein 189

Willow Valley vein 189

Franklin- Hiiiwey vein 188

Bm keyr vein 190

Texiiw vein 'yHiem 190

Miiri liie veiiiH 191

Miinyiot Tl.. l ittl. I r Creek Baain UU

Caledonia vein U£2

Kingnl'iiry veins 192

St. I.ouin vein

May lower complex 194

firant vein UJfi

;reennian vein IM

I'll inn vein 121

Banner vein UiH

Xorlh Banner veins ISg

Chaptkr XV.— Detailed desi'riptiona (contiuuedj 200

Nevada City diatrict 200

Minl,..ll:n. , 2Q1

Morning Star and Kureka vein 201

I'lttsliiiri; I i em 'JifJ

Mohigau Vein 205

Merriniac vein 2i£

Ka;:le veiii

Contents. 9

Chaitkr XV. — Detailed dcacriptionii — C'ontinned.

Nevada City iliiricl— ContiniitHl."

G"i'i I iinnel vein 2QI

Miiiiiitaiueer vein

Mi rnl'u lil vein 209

I riil and oiiiiiii veins 212

Joliii liiill. Seventy-gix. and Kirkbani veiuM 211

The seam belt 218

Pro Film. Veliiw Diiiniond. and other elaine> 219

Graaw Valley district 221

The Idaho Hy.stcui 221

Alpha. Kentucky, and Sprint; HUl veiuit 221

St..l.din ininn 223

Eurekii-Malio-Mitryland vein 224

Iji'veiiHiiiiints 224

Outcropw and ronntry rock 224

Tlie ore 228

Struftnre of .re 228

I'ayahiwit 229

South Idaho vein 22M

Bninwwiek group of reins 229

i;nion vein 22Q

t'ainbridtie vein 231

I'raiii fort I'in . . . .

Crown I'oint vein , , 231

Badger Hill vein 232

veins 232

The veins of (lold Hill. .Massaehnaetta Hill, Kod vieinity 233

(iold llill K'oi ky li.ir v. in 233

yliangliui veina 2.t4

Hhx Ledge 234

C'iiii iiinati Hill, Scotia, and Twrillghl vciua 234

r, ;>Im.i1> vein 234

Jc r-i'v li'ui' and Htrinoa veina 235

Hill vein 235

Hone 11.11 vein

The veins in the vicinity of New York Hill and North Star 2'My

KiMiiiHt Hnil Irinh Aiiitrieitii v..iri<.

New York Hill vein 221

N. w lio. kv Bar vein 221

Iiikurinan vein 238

Lamanme vein 238

>i.-irvein 238

Cniiiil 1 y lock 238

Tliu OI L 239

Dr.. hlioo|.< Zhl

Fa.ilts 240

Contents.

CHAiTrK XVI.— Dftjilcd tlcucriptionii— Contlnned.

Gnwg Vallpy tlixtrict. — Contiiined.

I >ni:ili:i vein - 211

Omnliii :iinl .Jack liiiiitm 241

llnmi'Miinl nniind tninw 212

Hftrttiry mine 243

Alli-'iiii Kiiiicli vrin 215

<lth. r V.M11S --- gjfi

The Forent Spring grow of mines 246

Parriii <ir Sluto i-in 1.'47

Vein yntt-niH of IViin-nylvania, W. Y. O. 1)., and tiie w'stcTii fiwit

OHlmrn.. Hill , 241

Pennsylvaiiin vein 248

Dimond. Bnllion, and AlMkn vein 250

>'r!iiikliii Mild other vein* 221

The Kniinr-< >nbonie Hill vein yatm 251

Einnire mine 252

>rl.'fiin iiiinn gru

lli'iisliin in 9'ti

Seliaiitopol vein 254

Ititltiirni. Mill iniim '.'XI

Lafayette and Cmm-t vein 2.'>(>

The veins of l{<nn;h and Heady ami Flat 2.'6

ll..u/lin'it.< Vint , 231

Seveii-lliirtv viii -257

CiiAmiR XVII.— HnnimarT 258

Iiifrn.1 iietinn i 2SS8

Geology 258

The tt.-unite gyntcnig 259

PriidiH tw vein fnriiintinii 229

StriirMim 21iQ

P*y BhooU 261

Th<- Hiipri jiicent formation 262

Addendum: I'rodnctionof XevmlaCity andOrnga \"alley diwlrictw in recent years -'fl2

Illustrations.

Plat* I. Gcnainl map showliig loeatioo of tbe acacia) abaata IS

II. Contour map nf tbn Xooceue aurfaea 108

III. SbfcU-tl T.iuf hi Mnin shot, Graaa Valley IM

IV. TUiii Heel ions ini; hi nn t iiri> of ... 132

V. Tbin twctiotiK showing ttlruL'ture of ore 134

Vt. Thin sectioiw diowiog atnwtnra ofoie 196

TIL Spacimena ahowlnf atraatoia ot on 198

VIII. Speeimena showing; Atmetare of ore 140

IX. Spci'inien fniiii Mcrri vein lion i i; l; '.t met ii rr of hi r . 142

X. Sperinn'ii from Merrilieitt veiu .ntriicturo of ore 144

XI. vein on tbe 1,400-foot lev>] 158

XII. Maryland vain, atapaa abova l,saO-foofc laval US

Xni. North Star vein, near 1,700-foot laral 158

XIV. North .<tnr vein, iiPiir level IfiO

W. Ophir Hill vi-in, Empire Diino, near level IBO

Hunker Hill vein, Amador County, Cal 160

XVII. Ore eboota of Xavada City and Oraaa Valley miaaa 162

X VIII. Ore ahoata of Karada City and Omaa Valley minea ItS

XIX. \'iew of Ptijiar Loaf and (.riipiil Hill from Nevada City

W. \'ii'w Clinnijiion iinil Uomu iiiiiicA from i'mvulenci* iiiiin-, looking

Doer Creek 210

XXI. Horizontal pneotioa and MCtlona of underground nurka of tbe

Prorideoee and attjolnlng minea 218

XXII. Map of the new Roeky Bar quartz mine 238

XX III. Muji of nmlerground works of North Star mine 240

XXn . Special map of Ni-vadii City an<! 'irass Valley mining ditttiata.. In poeket.

9. Primary pyrrhotita In nnicita 67

9. IntergTowth of primary pyrite, pyrrbotite, and ilmanlte 70

4. 8ertion nf nnperjacent formations at Manznnita mine 98

5. Hlilff at liydraiilir nit, ni'ur rity re.iervoir. Nevail.-i it y . M9

6. Sei-tion of breii'<t of workings. West Hannony drift uiiiie UK)

7. Vertical Kectiou alou; West Harmony Inellna 100

8. Vertical aection along Yoeamit* incline. 101

9. Sention bi working* of Odin drift mkne lOt

10. zone in ma!io.linrit<-. Detr Creek. llelU-fonntnin mine 185

11. Vertical HOCtiou uloii;; hliuft, Feilern! Loan vein 187

13. Vcrtii'iil aection along Bliiift, Xe*-er rat \oin 188

13. Vartioal aection bowing faulta ou tbe iieckman vein, Mayliower

mine im

14. Hori/.Kiital projection ahovin fanltM on the lloyd vein, Mayflower

mine I!*."'

15. Vertical section along shaft, Canada Hill mmh

16. Hariaontal projaetionabowing fanlta ou tbe Canaal Hill vein 197

17. WnodTllIa rein, North Banner ntna, in drift 198

19. Vertical aactlon along abaft. Pittsburg vain 90S

Fio. 19. SeetUm of Plttoborg alnlh Ievl 904

30. Mmp of Oro Fino mnd otbr cUiras 919

21. Vertical uctiou tbruugh St..TuLu shaft 223

22. Vein ill .st..)<iliii iiiiiic, liftli 1.") fret lasl of shafl 223

2a. Vein in 8t. Jbn mini*, liflh level, lU) feet weMiut' ahad 223

31. Croat wsctiun of Enreka vein, 300-foot levol 225

9S. Cem Motion of MuyUnil via In otoparf nbovo 1,300-lbot lovel 999

99. Cmwaoetion of Maryland votn In atop atrnTO l,iSflOAiot loTol 99B

27. Verticul siH'liiiii llirimU I'liri-k.'i htial'r, sbi>\viiit; veiiia. 287

28. Approximate iiiitline of tlii. pay alioot 998

21i. (.'roiM section of the veiu, IcTol.. 990

SO. Longitodinal aeotion, Union Hill miu, showing nnaa atopod SSI

31. Vortical aeetion alonK shaft. Oninlia vin 949

39. Kection, sliou ui;: fiiilt, iiiiilia iiiiiu>, fuarttHiith li'vcl.. 24

33. LoDKitudinal liiiM'tioii, WisronHui iiiiiif, hIiowiii iireaH Htoped 244

'M. Vertical section nioii); sliaft. Norauiba|;iia vein 346

35. Vortieal aoetion along sban, ahowing voiua and cross fiaooraa, in tbo

Paoaaylvanla nine 943

S6b Hori/uiitul projdctioii of coiitncUt on Hurface nnil on the plane of the

37. Longltadinnl aaetion, aiwinng ntt, Opbu Hill vein, twontietli levol,

Empire mine 353

Diyilizua by GoOgle

THE VKINS of NEVAHA ("ITV AND UHAiSS ALLEV DISTKICTIS, CAUFOKiNlA.

liy WAI.DBMAK lilKlMiBBir.

CIIAPTBB I. INTRODUCTIOX. mXAi WORK AND ACKNOWLEDGMENTS.

The field work uu wbioii thin report in buHcil was bgua iSepteiuLH-r 90, IMS, Mid oontinaed witboat intennption until Joiie 28, 1804. The iiiiiiw tisi il wcie jii ii:ii in Ifl'l hy Messrs. A. F. Dunuiugtoii and U. H. .MiirMliall, with tiiaugiilation by Mr. K. M. DoaglH, on a scale of i t};;, or about 4 inches to the mile. They comprise three slu-ets, eai'U nhoiit I'J miles, naiiuMl icsiicrtivcly the Nevada City, liaiinur liill, and (.irass Volley sheet. The geulugicai aud maps, the latter vith the outline of mluinf claims indicated, liavf Im'cii imMisIicil ;i< a folio of the Geologic Atlas of the I'liittHl iStates. For present a map on the reduced scale of .l, v,n has been proiinred froin the ftill-sixe sheets of the folio.

The chemical analvM'N liave been made by Messrs. W, P. Hillirand, H. IS, Stokes, George titeiger, aud Peter Firetuau.

To the mine owners and snperintendents of the districts many thanks are dne for the courtesy and aistaiice extendtnl by them in the veork of exaniininfr the niiiies. 1 also take jxrvnt jdeasure in uiy special obligation to .Mr. H. C. L'ren, of Grass Valley, and Messrs. W. F. Englebrtght and W. W. Waggoner, of Nevada City, for much valuable information and cooperation.

Obooraphic Position.

Tlif f.int niiiiinj; district-* lictc (lcs<;ribed are located in Nevatla County, on the long western slope of the Sierra Nevada, at au average elevation of 2,.'!00 feet and about 15 miles north-northwest of the town of Colfax, on the Central Pacilir Kailroad.

The ninp appendwl this paper slows tlie topoprapliy and geolofry OU a scale of about 2 inches to the mile. The northern part comprises the Nevada City sheet on the west and the Banner Hill sheet on the ea.Ht. The southern and Ninaller iarf consist-, of the (Iiass Valley sheet; the small area uiappel outside of the northeastern corner of this sheet is referred to as the Bmnewick traet.

Diyilizua by GoOgle

14 TBIMS OP VEYADA dTT JJSD ORASS VALLEY.

Topography. Relief.

TlMMliHuiuiitiii.: t'<".ttureti iu tlu' noi tluTn part of tlicfriu l are the two loug ridges whose crests deweud gently westwurU— the ilunuuuy liidge, near the northern boondiuy, and the Banner Hfll-Tvirntallc Ridge, near the southern houiidury. The northern ridge sinks \vitli a rndunl ship (torn an elevation of .'i,<;60 feet to 2,840 feet at the we.stern boundary line of the Nevada City map, and in cut iu two by a gap north of Nevada City. A eonspicuouK hill, the Sugarloaf, with an elevation of .'$,07." i't'ct, staiuls ill the middle of the trap and reaehes at its Biinimit the gradient of the ndgo line. The 8outhern ridge, beginning at an elevation of 3,600 ftet, to somewhat wider than the northern, and has at the western boundary line of the map an elevation of 2,70() feet. Kear Banner Uill this ridge is cut in two by the narrow canyon of Little Deer Oreek; forther weetsevenil pips are cnt across it, the most prominent one being that at Towutalk. The averajje sIojk' of the ridge line is At the eastern bomidaiy of the IJamn r llill district the

ridges uppi'oack eaM:h other, and are in fu't Nepiuuleil only by the deep canyon of Deer Hreek. In the southeast comer of the Banner Hill trac t, toweriiijr feet above the ridjres, stands rlie isolated and conspicuous banner Uill (elevation 3,904 feet). From the edges of the ridge tables steep slopes lead down to the watercourses, steepest as a rule near the summit, then out somewhat, then agidn bcom> iufr stee|>er toward the stream Tlie (listaiicc lietween the ridges is greatest at the western eilge of the Nevada City tract, and here, as well as south of Nevada Cit, the relief is leas accentnatsd.

Till-pcMcnil relief of rln' (Jrass X'alley truer is uciiflrr and the outlines are more undulating than those of the region described above. The elevations range from 3,080 feet on the summit of Osborne Hill to 3,080 in the bed of Wolf Creels, at the southern boundary. The north eastern part consists of a series rather flat tojiped rid'es, 200 to feet high, with comparatively steep slopes toward the watercourses. The larger, southwestern part may be considered as an undulating lilateau, with somewliat n rejnlar liills and rid<,'rs risinfr to a hei'htof I0<) or 'Mii feet above the general level. In this plateau the principal drainage line has cot a eanyou, which in some places is narrow anil steep, and the depth of which does not exceed 300 feet. I.'isii:;,' liih the otlier relief and occupying a position similar to that of Banner Uill, stands the high ridge of Osborne Hill.

Tlu ]riiicipal stream is Deer ('reck, wliicli traverses the middle of the regmu from east to west, and which, 111 miles lurtiier west, empties into the Tuba River. The total tM of the stream from the eastern side of the Banner Hill tract (elevation, 2,840 feet) to the western side

Diyilizua by GoOgle

.

Topoorapht And Lttbsatukb. 15

ul' the >evada City tract ((lovutiou, 2,1GU leet) isi G80 leut, or about lUO feet to thA mikk The &11 is by no means nBtfbnn, however. In the sti'c]) funynii in tlie eastern jiarf of the Baiiiifi- Hill tract ir is 150 f't;et tu the luile; llteiicc duwu to 'evaUu City about lUU tut to the mile; from Xevads City to the Providence mine, through ftoother narrow runyuii, tbc fall ih I.V) (Vet to thr inilr; atnl from the PrOVideuce down to the edge the tract it is hut fet*t to the mile, the creek raejuideriug over grave'Uy flats. Lateral raviueH, usually 8tecp and narrow, lead to the creek from north and south. A somewhat larger tributary is Tattle Peer f" reek, wliieh heads in the Vieinity of Raiiiior Ilill. South of Towntalk the drainage ih toward Bear Kiver, the ravines I'ornimg the northern headwaters of Wolf Greek, a tributary of that river. Southeast of Banner Hill the steep ravines lead dtiwn toward Oreetihoru Creek, also a tributary or Bear Hiver. The larger part of the area iu the southern of the tract is drained by Wolf Creek, a tributary of Bear River. Prom the city of Grass Valley it runs south to the limit of the thief without larger tributaries. At dress Valley it forks into two creeks, whivb have a general eat-west direction. The &U varies from 50 l%et to the mile in the Grass Valkiy basin to 130 in the vicinity of the Otnaha mine. The smaller tributaries to the creek show a feature whieli is also marked in the other two tracts, though to a less extent; they How with gentle grade over the undulating, plateau-like fwuntry. even forming marshes at their sooioca, but on approaching the main stream they desreiMl it with a stwj), torrential grade. East of Osborne Hill the drainage is toward itattlesnake Creek, a tributary of Wolf Creek. The extreme nofthwestom comer drains to Deer Creek.

Vbobtation.

Tlie vegetation is of generally nnifbrm character fhrongfaoiit tiie district, and consists predoniiiiaiitly of a second growth of yellow pine {I'iHUM the much more luxuriant growth once covering a large imrt of the ground having been cut for mining puriioses since 1849. A few large white oaks are found on the more open flats, and a strong bushy growth of chaparral (Man74anita and Ceanothus) covers some of the bills. The serpentine ridges have a seimrate and peculiar ▼fetation of digger-pirn (PiM foMaiamt)— elsewhere rarely growing above 2,000 feet— yew, stunted oak, and thomy bushes.

Litbraturb.

Tlie references to the mining industries of the districts are very seafcterwl

ami con.si.-t chiefly in descriptions of individual mines. The nioro iuijiortuut of tbem are contained in the following list In the preparation of this report the statements in Bean's Directory, Raymond's and J. Boss Browne's re|>ort8, Burcbanl's mint reports, and the reports of the. State mineralogist have been frequently consulted and used. Beau's

Diyilizoa by vOOiC

16 OOLD-QUARTZ VEnra OP NEVADA CITT AND GRASS VALLEY.

Directory is uuqtieHtiouably the best aud must extensive aa well as the most relwble extant of the diatricts up to the year 3866. In these publications tlie eolo'ical featines generally iKnpy a very Hnb- .spiUT, most obstrvatioiis lu'iiir ' 'Hifliied to character of vwns aud ore pniductiou, and tecluiicul tiula.

W. P. Blake. EsplontioiM aod rarveT* fttr nNlraad roato from Ifaa UlHlMippi RiVr to tiM PMllla OcMB, Vol. V, p. 268.

niBcIf in 1H.VI f'ontalnii Inlrmmlit In rrgunl lu ! hi' Knipiro jiml Ciold Hill vcirii i tc.

.Iiiii.v S. IIiTTKl.l,. MinitiK III till- I'ili itii- Stats'H of Nortli AiinTica. Sau l'riint ic(>, mu. 2-2i ]iagc8.

P. Laur. Da giaenMOt et I'exploration I'ur ou Califonii*. Aon. dea mines, Vol.m. 1868, p. 412.

Wotpii from niMiv niiui'i io tiM vidBttj. AdTMMilMTirliHyafaorqiiaitBvataaMidcniMil

J. Bum Bbowhs. Haport npoo the niiMral raaouroM of the State Twrritoriw wwt the Boeky lleantelM. WMhtagton, U87.

Qnfliw nMM M uMiiy bIbm the dirtrirt. tablM of pradmitlMi and atoBpa, atalMMela mdy aiiatoK law.to. ; alw rfaMagAbr WIIHaM Aahkmw m tbaGtMa Valtoj mlaaa.

J. Row Brdwnk. I.Vport the niiii< r:il r<-niirr(>)t of tlie Statea and Tenitoriae

(>dUIiu uatrit vf many niiDM iu tbo district, rfairfly from Ban' DIrwitory.

Bbm Silumah, Jr. Kotm on the Onu Vallajr miBinit diaferiet. Am. Joar. 8oi., Sd

('imtJiinH iiMil Holes III' tM-\ er.ll liriiH-. n uM". tKitalilN of lln- Knn'i.a nnf.-

Ill ri'tiiril to tin- 't ..|o J lit I i r.i"K -y . i-tr, Tr hI'i .i-mt II m - jvcaki of 111.- n'*'i:.-.toiii .im |iroliiilil\ alien il .t ihim nl n li't 1 1n- nn'Mvui i- i. to 1 1 n i .iii'l a !:r i -i i on ri* I ! lo qiiartK vriim im rniifuriiiliiu to tlio i.triiijtii iition, '1 ho Jiuntin.' or ..1 i i tin li,... ' nj. iii; ii- i-n mlaWken for ulnllfliMiliaD. ore kIhwU ix exctllvully cxplaluol. ami ttie vivwuf taipovwtabBMet la dplh iawNBlMti.

Br.\n's IIi.s'KiitY or Kxvada Conrrr. Compiled by Edwin

An rxcrlU'Dt IxHih. giTinii Iii*lar1eal data of tliv dpveloiHDeiit of tb dintrirl, aa datallad nolan in regard to tuvulj armtj vain and placer tbrn wvrkad, ebfalljr in rtgcard to jIaU aadvawMMblik Oet af prtot and vacy ma.

R. \V. HeiKii t .iti ilif iniiuTiil rt-Kimn i.i' tlir .stiiti-n anil Tetritartaa weat of the liockj* Jiluuntamx, VoIh. 1 to VIII, <'uiu|)ri8iiig lt*t31}<77.

Cantalea naaiaraiia nolm fn ivgard to mtuea af tka iHirtHet.

Amcm Bowman. Report on the ]>ropertier antl ilnniain of the Califoruin Water Compaajri aitnated uii tbe UorKtuwii divide. San Fraociaco, A. L. Baovrolt A Co., 1R74. Alao In Raymoml reporta. Vol. VII. WIS, pp. 441-470.

CiintmiiB a fi w nnli'it on (iraisii Vullry iiimox niiil many rrfi ri-nn'ii Iii nlliiT loi'jilill in thi> Gold Bolt. .\Uurnlatni> mapalmwlDf alrlkeof tfa mml linpurianl voiaa uf ibatSnid IMU Baak very raieand oat af print.

II. C Bi'RCllARn. Report of the Iiri-rtor of the Mint iiimn thiitatifttieK of tlie piodiictioa of tbe preciooM uieUls m the rooted States. ItftHl, imt, 1883, 1884.

Contain* noaieroiia nalaa, chiefly i-n thi' iirednction of ifavada City and Oiaaa Tallajr mlnaa.

J. D. WlllTNcv. The iiiirifenraagraveUof the .Sierra of CalifiBrDin. Hemoiva. MuR. Conip. /.uol. Marvnrd Coll . ol VI. No. 1. f'.wihridL;!-, IsSfV

Nola aud uf miuva lu tlin illatrivln, by J. J). WUituev aad \V. U. I'attea.

Diyiiized by

Lrbbature And Histoby.

Biwmn or tbm Svatb UaaauMtout Cauvouu. ftaMtHMntg;, CaL Tola. ItoXII,U80to18flS.

VUHroat nutit and ilraMrripUoaa of qnarts Mid piMW iB th ilUtrlot, by MelvlU

AttWMd, J. B. HobnoQ. aod K. A Wntara. Ako a paper on the " LllboloKy of Wall-loolu" llj UalTllle Attwood, dccrlbliig the Eureka and Idabu raiOM (8th Ann. Kept., Jfp. HX-VM.) AUw m map by Boia E. Bromw, of Ui Harnony grvTvl mtneii (ISth Ann. Rcpt.).

J. Artuob Phillips. The mining and metallurgy of gold and ailver. London, 1888.

OaMalM rnilwftam personal obaei latfam on wmie Oraaa Valley laea, and alao exoelleat

titiaervation* on ore cti\ Sbowg thjit ihr old ort-t do not decreaaiiu tenor with depth.

K. (t. C'oHMMJ. The gold quartz minm of (irass Valley, I'al. Kng. and Mlii. .lour., Dec. 11, Dm, p. 418.

£. Rbykr. Ueber die Ooldgewiiuuiiig in Califoraiea. Zeitaoh. fUr Ueig- , Uiittaiiniid SalinenwmeB im prean. Btasto, VoL ZXXIV, pp. 1-28, USB.

Gculogienl Ii .if V:illny and NvTadii City; Kurt k.i ii:ni 1 l .l.i. iiiinoa.

The dstsnaiiiaUon of nick la nut AttoigaUier —ttoftitocy; data |irecotMl BjiiwrvnUy abow* lag gmdnd taiMM to valoe or WW ia difftfe.

Odd(|wrti. Tnas. AiD.Int.lfia.BBg., Vid.XVlII,pp.6a0-M4

NxvAOA Couirrr Mtmiio Rbvxbw. Pabliahed by tlM Daily Morning Unioo. Graaa

History.*

Pievioiu to the middle of the prewat century this region, as well as the whole Siemi Ni viMlu, wm sn nabrokeu wilderness; the rt'gion

above un elevation of L',(MM) ft-et wsia eoverefl with niagiiificeiit forests ol suar piue, yellow pnie, aud lir. Nevada City anil Gra8 Valley were located at the lower limit of this laxariant and viririn (brat.

Once ojm'IumI up by the army nf u'dld seekers. t!ic |iiiiLri< ss of the country was rapitl; marveloii.s indeed are the chaogcji wrought in the itforf y-eight yeaiM eluiisc d since the disoorery of the gold in 1848.

The tn (l!seo%-ery of jold in the Sierra Nevada is, a.s is well known, credited .1. W. Marshall, who on .laimary 19, 1818, lonnd some nnpgets in the null-race while vunstnu-ting a siiwuiill at Colonia, Eldorado Gonnty, for General Sntter, of Sntter's Fort, now Saeramento.

The first 'old found within the boundaries of Coniity is snid to have been panned out by Jonas iSpeut on liosie liar, on the Yuba Biver, north of SmartsvQlet Jane 2, 1848. Marshall himself is stated to have visitetl Nevada Goanty in the summer of 1848, while eeoortlng a party of immigrants across the moantains. He camped on Deer Creek, near where Nevada City now stands, aud tried a few pons of dirt, finding gold each time. lu October, 1848, two prospectors came u]) Wolf Creek and enmpt'd a short time near where the Eiueka and Idaho mines are now located.

During the summer and Ihll of 1849 the miners gradually wwked up along the Middle and South Yuba, Bear Kiver, Deer Creek, aud their

Mn MafhMMiaal ravtavtbe MBtM amittoaadatove have fcteaftef

dnwB upon.

18 Oolduartz Tsins Of Nbyada. Citt Axd Grabs Tallet.

priucipal trilmtarics. Several men were camping at Boston and Batlger Uill, Grus.s Valley. Dr. Caldwell built the first store where 2fevaUsi City now stands, and sawmills were erected 4 miles sonth of Grass Valley. From that tinjo the dovelopinent of the districts, at first based pi iiicii>:illy upon tlu alluviiil ]i1;M t'r iniiics, went forwanl. Ill March, ISM, uu alcalde was elected under ttic iMexiciin law ut Caldweirs store, and the camp received its name of Nevada. In ApirO of the same year tlie first hotel in Nevada City was orcrtod. It Imilt of rifted pine boards, the whole house, 6 feet frout and 46 in do)>th, being taken from one tree. The house opened on May 1 with 40 enesta, the moderate price of board and lodging being $25 per week.

A town, railed ('oyott'villc, prow up on the grav'l liills in the northwestern part ot the present Nevada Oity as soou as it was found that the hill gravels were rich. Several thousand men shed in daring ISTAl Sawmills wt'ir iTCCted, and the lunilxT sohl at 1,000 In the sammcr of 1S50 a ohureb was organized, and a paper appeared in 18S1. In 1853 the first brick building was erected, and teleiurraphic couinmnication with Sacramento anl Murysville Wius estal lislicd. In there were 907 occnjued houses in Nevada IMty.

In lirass Valley several stores were oiwued in 184U and ISM. The first town election was held in November, 1800. The first chnrch was ortianized in 1851. and a srliool with ]'2 pnjiils (tpcncd in a log cabin tlie same year. Alter 1851 the growth of the town wits very rapid. Like Nevada City, it was, however, snbjeet to many rinctnatlons, caused by several rushes of the miners to newly reported iold regions, and by periods of depression and activity in the quartz-mining business.

lu 1880 there were 20,3:i inhabitants in Nevada County; in 1890, aooording to the last census, 17,369. This decrease is dire<-tly dneto the cessation of liydraulic mining, jirohibited shortly after the census of 1880 by the Federal courts, on account of damage wrought to the lowlands of Sacramento Valley.

Grass Valley townsliii) bad in LSHO a population of 0,088; in 1890, 6,798. The of the cily is not given separately. Nevada City township had in 1880 a of 5,506; in 1890,4,013. The IJopiUation of Nevatla City is piveu as 4,022 in 1880, and 2,324 in 1890. Siiir<' is'M) both cities have incrciised not inc/)nsiderably in populatioiif due to the renewed interest in qnar)/ mining.

Development Ok Mining Interests.

Plackb Mining.

Burinp the first years the alluvial placer mines furnisbed the largest amount of gold; in both district-s such mines were actively worked doling the first and even the second decade after the disoovery. Very soon, however, the older. Tertiary hill travels were discovered; the deposit) of these were far richer and more abundant at Nevada City than in Grass Valley. Between IfiGft and 1860, and between I8fi5 and

Diyilizua by GoOgle

DETELOPMEliT OF MIXING IMTEBEST8.

the old <>hiinnols on the Alta, Towiitalk. and IndoptiideTit hills, ueur Urass Valley, were worked by the dritliug process. Vury little bydnmlio work was done about OraM VaHey. At the present titne there are iimctically im placer iniiu's working in that vicinity.

As early as I80I the hill gravels above Nevada City, both on the 8oath and on the north side of the Sugarloaf, were discovered, and the town of Cioyoteville, already alluded to, was established on the eastern end of Lost nill. The iMctluxls of iiiiniuf; were at first small shafts being sunk and low drifts run in diQ'ereut directions. Sluices, the first on the pan, rocker, and were first nsed, it i-s said, in the Coyoteville di;;;,nnf;s. In 1S33 tbe first exixTiiuonts in hydraulic mining, or slaiciug with water under higb pressure, were made fn Nevada Ctty, on American Bill, by E. G. Matteaon. During the sixth and seventh decade hydraulic mining; was carried on extra< Bivcly at><)iit Xcvadii <'ity. \\iifin>: in IStUi, Kean remarks in his directory: "The phvcer mines are still worked quite extensively and are the main reliance of a Imko proportion of the population. There are a few companies conducting operatiotia on a large scale, and generally with success, liesides numerous iudepeudent miuers workiug the gnlchea and ravines.'* At this time bydranlic plants were in operation on American Hill, Wet Hill, and Ist Hill; extensive ground sluicing was carried on on the head waters of Brush Creek, about Selby riut, where the shallow gravels were extraordinarily rich. lu 18B8 to 1860 tiie fieb Kebnuka gnmnd of the Manomitaiannel was In ISTO the hydraulic mine on the Manzanita chaniu'l was being worked. The last hydraulic work about 2ievada City at the time of the snppreeaioii of hydraulic mining was in the extreme northwest corner of the large hydraulic area on American Qdl, and is referred to as Hirshmauu'S Cut. Since 181H) several drift mines have been in 0[>eratiou ou the Harmony Bidge, notably the East and the West Harmony mines.

The first find of gold-bearing <iuartz was made on Gold Hill by a German in September, 18o(). Thi jiiece was aold for #5, and proved to be worth -KK).' These and other tinds were at first not thought much of. I3ut iu November, 1850, a rich ore shoot was struck on Gold Hill by miners digging a bole for tbr cabin chimney; pieces of this vein

prov'd to contain per ton. A great excitement followed, and in this and the two following years most of the qnortz veins iuthe virginity were located. At first tiie quarts was enuiied in mortars with spn ng pole, and the I lafV company took oat $20,000 in this way in the winter

and spring of 1S51.

The first mill was put ui> in .lanuary, 1S51. It was a rude alhiir and

LetUr by Seuiitor A. A. Sareot, written Juiuary 1, UM, and paldUlieo tu tJin >'va4a Tnoacript,

20 Oold-Quartz Yeinb Op 17Btada Citt Akd Grabs Tallet.

proved practically uaeletiH. A aecoud, 8-Ktanip mill was erected soon alter, wkieh ww a litUe more naelta]. Book from Gold Hill waa enished

in it fiw $60 per ton. Tbeiniuers were paid $12 (ler day. In tbe followitifr years n nnmlier of mills were built, one of tho best bpiiifj oi-wted bj' Melville Attwood ia lu 1853 W. 1>. Blake writeti that several

miUs mm located akmg Boston BavinA, ud desertbM tbe process* in nsc at the mill of the inino, which began to work in 1851, and with brief intermissions has contiuaed until to-day. Whitney' writes at the same time that with ttie beginning of 18B8 Uieie vera at least 20 AnKlo-Caiitorniaii companies in tiie London maitotf ropresentiug a capital of

During 1851 there was a great excitement about quartz claims in Nemda Oi, rich sold qwwts haviag been diseovend. The Mertifield, Providence, and Gold Tunnel veins were loeatnl, and dnriufr the next year expensive redaction works were erected, ad of which except the Gold Tnnnel mill were oonspicuons IWInTes. Orer 180,000 wen expended by the Hunker Hill" company on a smelting pioeess, worlcs for whieli were erected on the present Nevada City chiim.

On account of the many failures, quartz mining at Grass Valley and Ifevada City received a serloas setbiick. At Grass Valley, where 8ev eral mills were keiit running, tbe industry slowly revived, hut at Nevada City the miners turned their attention to the gravels, and quartz mining was almost neglected. In 1867 Grass Valley was flourishing and Nevada Olty mines were From to 18<!'2 the business was depressed and values in both districts depreciated greatly, owing jiartly to the gre4it Washoe excitement, pai'tly to the UcMuling of many mines during the winter of 1861-02. Again matters improved, and in 1867 Grass Valley was the most prominent camp in tlie State. In according to .1. Ituss Browne, there were 248 stamps, crushing llfiHiO tons of ore, with an average yield of $30 to $35, in Grass Valley, and 142 stamps, crusbin;; 14,L'(K) tons, averaging $25, in Nevada City.

In 1873 (Uaymoud's report) tbe Grass Valley district ]>roduced about $2,000,000 (estifflato of large mines only), raising CU,UOO tons of ore, averaging $33, with 1 or 2 cent sulphurets, while in Kex aila Ci only $07,uoo was piodnood liom 9,000 tons of ore, averaging $7.60 per ton.

In 1880, aooording to the Tenth Oensas, 28,980 tons of ore were raised

in tlic Grass Valley district, averaging *2().L*<); in the Nevada City district, 27,814 tons, averaging $22.52; and in the Willow Valley district, 1,030 tons, averaging 840. Neither the Tenth nor the Eleventh Censua gives the numtier of sbimps running. From the latter there are no definite data to be obtained, the production of the county only being given.

Aooordhig to the table by Mr. J. B. Hebson, in ttae Tenth Annual Report of the State Mineralogist for 1889, there were, during that year,

lUMUo WMlUiartto Oailad flMaa, FkiMaipUi, IIBC p. lt.

Diyilizua by GoOgle

Development Of Mining Intkrest8.

211 Rtamps in Grass Valley, criisliintj (>!>,().>i tons of ore containing 1,721 totiH salphuretH, or 2 per ceut, with a total etimuted value uf tree gold and snlphofete of about flfiBOiOOO, or about $18 per ton; in NoTada City, 172 stamps, crushing .W,(K)(> tons of ore containing tons of gulphnrets, or nearly 4 per ceut, with a total value of tree gold and anlplniTeta of about t4A2,500, or about $12 ywr ton.

A very decided improvement in the qnartz-inining bnsinesH wbb noticed in the beginning of the ])re.sent decade. Wliih; in 18So tliere vrero but few mines running and but little itrospecting in progress a gnat and incronaod aotlvity was noted at the time thie investigation was begun. Two Imndrcd and fifteen stamps were dropping in Orass Valley and 17U iu Nevada City during 1893, and several new mills Lave been erected since then.

Gold nill and Massachusetts Tlill were the principal the first two Tiu- Empire Las worked almost coutinnously since 1851. The North Star wa in operation until 1872, then again from 188t to the present time. The Bmeka poj shoot began to bo expSoited in 1864, and has lu'cit continuously worked since then in the Eureka, Idaho, and Maryland utiues. At Nevada City the Gold Tunnel and Califomia mines were among the earliest worked. The Piovidenee and Nevada City mines have been exploited almost continuonaly, with short interruptions. The Sneath and 'lay and the lMttburg were large producers during the sixth and seventh decades. The Willow Valley veins have been worked intenulttenti.

In 18M the fbUowing mines were prodnetng:

NfeVADf Girr.

DrfftWtiMri.—¥.:iHt H;iriniiiiy Wct I lanuony .

QtuartM iM.— Chftiupiou, Providoucu, Novad* Cit, Majllower, i;'edonl Lou, utA nttohiirg.

Omm Vaixby.

Quart: mira.— Mnr.vlauil, Kiupin?. North Star, W. y.O.D., PBrnNylTUU Ekottfo, Omaha, Slate Ledge, Oaborne Hill, and Orlaana.

MIHI2IO OXtAIHS.

Tlie first meeting of miners was held in Grass Valley January 13, 1851, on MiMsachusettH Hill, when a size of 30 by 40 feet was allowed for all claims, the boundaries in all crises being perpendicular. Later on claims 100 feet square were allowed. The form of the quartz claims on MassachnsK'tts Hill still shows the outlines of the earliest locations. tStill later, iu 1852, a uniform rule was adopted by the quartz uiiuers of Nevada Oonnty by which each prospector shall hereafter be entitled to lfM feet on a quartz lodge or vein and the di-scoverer shall be allowed lOO feet additional. Each claim shall Include all the dips, angles, and variations of the vein." (Boss Bcownes Report, Washington, 18G7, p.m} This was still in five in 1866, and in fiiet until the Ftodend

22 Oold-Cuartz Veins Of Nevada City And Oba89 Valley.

miniiifr Irtwsworopiussed in 1872, iillowiiifi quartz claims to be 1.500 feet along the veiu, with all tbe Mpurs, and angles, and GOO feet wide.

Procb88B8 Of Minino And Milunq.

Tlie scope of this paper does not jim mit a detailed explanation of the processes nsed iu obtaiuiug tbe gold from the gravel and the quartx. A few uotes ou tbe Rubject may, howttrtTf not be oiiuMi for thoee not fMDilicr with the methoda emidioyed.

HVDRAFLir MTNTNO.

This method coasists iu direuliug a stream of water under xiressure, ranging up to 400 fiaet, against high gravel hmlca. The quantity of water in one jet ranges up to 1,000 or even 1,500 miner's indies (10,000 to 15,000 gallons per minute, approximately). The disintegrating ))ower of tbe jet is often aided by bank blasting, consisting in run. ning small drifts in the bank and exploding heavy charges — up to 2.'),000 iKHiiids — of Maek Tbe gravel is tlien led throagb ft of sluice boxes, aggregating at least 1,000 feet in length, in which the gold is eaaght in riffles of cobblestones or wooden blocks by the aid of added qnicksilTCP. There are no data of the yield or cost of the hydraulic mining in levada City. Presumably, it was not much different from that of the other lar'e hydranlic mines in the county. The top gravel is usually poor, containing from 2 to 10 cents per cubic yanl, while the loweHt part on tlie bed rock may I'cveiyrich. The minimum cost is probably about 3 cents per cubic yard.

ram HunKo.

This inefliod consistB in extracting the richet gravel on the bed ro<!k of the old channels, opened up by means of tunnels, inclines, or vertical shafts. The gravel is rarely worketl to a height of over 8 feet, tbe gold being mostly concentrated near the bed rock. The deposit is

oxit and in a imnnior similar to the working' of horizontal coal seams. The pay gravel is ia sluices, rarely aggregating mon than s ttnr hundred fieet in length, or when hud and

cemented is crushed in stamp mills.

Tbe cost varies greatly, according to conditions. Under the most favorable circumstances the may be reduced to !H) cents per cubic yard; in mines worked by shafts or inclines, having to hoist the navel and pnnip the water, the expense is increased to A'i or The milling of tbe gravel, when necessary, is usually cousidered to cost cents per too.

Quaktz Kihiko.

The method almost universally adopted of exploiting the quartz veins is by incline shafts, fidlowing the dip of the deposits. Levels

Diyilizua by GoOgle

are turned vusaaXfyvnry 100 feet, and the pay rook is extracted by overhand stopin'. Perpendieolar ahafls are sometimes nsed to open veins

with tiatter dip.

The oost of mining yariea ooiundnbly with the thioknesB of the V( ill. tlie hardness of the oonntry roelc, and tlie depth and amount of

water in tbi' mine. The fenorally narrow vein.** of fJiass Valley Tifcoasitate ao much dead work that the expenses aje rather high. In tlie lari!* veius of Se?ada City the oost is stated in the mfaieralogia reports to ti) ton, whih' in the forth Star, a rcprcsenta tive deep mine with narrow vein, it is In certain mines of Grass Valley, worlcing under disadrautages, it is even mote— up to t6 and $7. oost of mining has decreased considembly in tho Inst twenty year.!*. J. Mom Browne fives the cost at the l''nipire mine a.s §8.60 per ton iu 1HG7, while at present it does not exceed H. The power used is steam, water, or elcetridiy.

The urea I'runi both mining districts are called " free milling'* — that is, they contain native gold easily amalgamating with qniokailver. Th

contain, al!*o. however, a certaiti of fjold chemically combined or very intimately mixed with the metallic sulpharets which make np a small fraction of the ore. However fine tiie ore is (trashed, there is always a certain, sometimes cotisiderable, amount of 'old going otT with the sulphur'fs if these jire allowed to eBcape. This was recognized early, and tlie suvinj; of the gold iu the sulphurets has been firand the most difflcolt problem in the milling process.

W. P. Blake desei ibed tlie jji ncpss in n.se at the Empire mill in 1><5,'J as follows: The ore, alter being roasted iu heaps, is crushed iu a mill; the pul|) passes over blankets, where much gold and pyrites is caught; these blankets are wrung out iu water attotsrvala, and the mixture of ohl and jtyrites is subjected to aiiialfjaniation in paus. From the blankets the pulp passes througti a icvoiving cylinder holding mercury, where a part of the fine gold is amalgamated; Anally tlie pill]) snbiected to an amalfjiimation in a jian liohling mercury and iruu balls; three-fourths of the gold is caught on the blankets. The gradnally elaborated process was in vse for many years and is known as the Grass Valley process. W. A. Skidmore le.s<'ribes it as used in the Idaho mill in Raymond's reports for 1S<;! and 1S70: The quartz is crushed very line; there is no amalgamatiou in the battery. From the battery tlie pnip is passed over blankets which are washed ont every (ifteen minutes. The results from the lilanket washiii<,'s are passed through two Attwood amalgamators, where a revolving cylinder with rakes stirs the mass in a bed of quicksilver. The skimmings of the amalgamators are treated in two Knox pans with chemicals, and here 3:5 per eent of the gross yield The pulp from blankets and amiUgamators is piissed in contact with revolving cylinders of

24 GOLD-gUAKTZ VEINS OF NEVADA CITY AND GRASS VALLEY.

amalfjamated copper and the Niilpbiin-ts concentrated on iuiproved CunuHli buddies. The HuljiliurelK are liiuiUy passed to the ehkrinfttion prooeM. The Twage oost of milling in 1888 was genenDy

over

The chloriuution process, obviating the shipping of the Bulpharets to ainaltbff works or the wairteflil grinding in ftualgftttittting pans, wm snooonflilly introduce4l in ibis region in ISGO by G. F. Deetken and

O, Maltman, and has been in nse contiiinally since that time. The snipburets are subjected to au oxidizing roaitiug, usually with addition of Dome chloride of Bodinm; fhe roasted ore is exposed to the action of chhjrine jjfas in large vats, and the chloride of gold fnnin'il is cxtriu tcd with water. From this solutiou the gold is precipitated in a metallic state by means of ftrrons sulphate. The silver is leached by ealoinm and as sulphide of sdver by calcium poJysnlpbide. Tlic charge of f rcatiiig 1 ton of sul])hiiret.s is from §1(> to AL'O. There arc several cbloruiation work8 to which tlie miners usually sell thtit ooooentratee. Mines with their own chlorination works report the cost to be $8 or pi r ton.

The process of the modern Stamp mill differs considerably from the old Grass Valley procesR. The ore is cmshed rook-breakers and (hd automatically to OOO-ponnd stamps droppingO toTinchcs from 80 to 90 times a minute. Amalgamation in battery is commonly used. Thirty to 40 mesh screens are used for the discharge, which is only on one side. From the battny the pnlppasaes over broad 4 by G foot silvered amalgamating plates. Fmin (lie iilati"; the pulp goes to the vanners, self-dischargiug coaceuti'ators of the endless-belt type, with lateral or longitudinal osoillation. In a few rainesi notably the Idaho-Maryland, the tailings from the concentrates are worked over again with different contrivances, but ordinarily they escape directly. The cost of milling has been greatly reduced in the last twenty years. In the North 2Star mill, under B. A. Abadie, snperintendeut, the oost during IH.S7 to 1893 82 cents per ton. The cost of milling in general may be said to vary between $1 and 50 cents ton, exclusive of the treatment of the sulphorets.

l,OS.S OF GOLD.

While the stamp mill has been very much improved and the loss of gold very maoh lessened, still there is in many cases unquestionably room for improvement. Some mills may work the ore vp to 80 per cent of the iisHay value,' but in the majority an average of 75 per cent only is recovered, and in individual cases the 1o.sh may be much greater. The mines wliose ore contains teHurium or mneh snlphnrets

are innticnliitly liiiMito lo.se nnich of the finely divided galena is especially liable Uy esca])e in the .shiice.s. A strict control

>Aediiig to J. U. Hamnond, 82 Ui M par omlof the MMy nUoa of tba wm mvoil la tb IbvtM n4 KrUi SlwMtlia.

0ver the procMS by coutiiiucd asKaya uf ore and tailings is too often leaking. Tb eonoentratora are made to work a palp oonststing of

grains of all sizes; in larger mills this could be obviated by proper sepai-ation of the pulp by streams of ascending water; canvas plants for the saving of the frequently rich, finest slimes are at present rather the exception than the rule. Rich sulphuretted ore, worth $75 and above, should never be but sliipped to smeltiiip works: the loiiKes in the. mill are in this case always heavy, and may euoruiuus if tellarlum fa also prtNwnt.

THB OTAMmB PROCS88.

Attempts tu introduce the cyanide process in this vicinity have thus fiur not succeeded. For tlie oonoentrates the prooesa ean hardly com-tc

w ifli till' The large uinouiits of tiiiliiigs to which it could have been applied have been swept down Deer Creek and Walt Gieek instead of being stored np. It is not improbable, though, that it could bo used fur many of the finest slimes, at present not utilised) as has been done at the Utiea mine in Calaveras Oonnty.

A. J. Bowie, Jr. Ftydranlic ininiiiu. Nfw York, 185,

J. H. I1ammum>. Tlte uiiriferons gravels of CaliforTiia. Ninth Kept. >Stte Minerul.iginl, 1H8!. pp. 106-138.

R. L. DuxN. Drift mining in CnUfoniia. Eighth Bept. Suta Minvnlogiiit, 1888, pp.'m-'m. mlnhig. Ninth Bapt State Hinanlogiat, 1888. piSBMSL J. H. Hammom>. Milling of gold orw hi OslUbnia. Eith Itept. State Hinor-

1888, pp. 6H6 7:15. E. B. I'RKsTuN. Oalifomia gold iiiill priictico. Stiit Miii. liiiroaii, Hull.O, lH!>r>. £. A. tiold milling at ttie North Star mine. Tntna. Aui. Inst. Min. Eng.,

Vol. XlIT, 1884.

Production.

To determine correctly the prcMluction of any mining; listrict in Cali* foriiiii since 1849 is ii well nigli lio]>ele."<s uiulertuking, so tleticient are the statistics. The best that ean be done is to present an estimate baaed vpon the known yield of later years and the estimated yield in tbeearlier time.-i. As the prmltiet of di.Htriets form an imjMjrtant part of tlie total gold production of California, that mt first be Btatetl in round flgarra. The tignres fbr the years 1848 to 1885, inoln- Hive, are taken from the estimate of Dr. II. Degroot;' for 18(>6 1S78 from the estimates of the Director of the Mint ; ' and from 1879 to the. present time the amounts have been determined by the Director of the Mint on the basis of more aoonrate infinrmatkm. The production ia given in millions nf dollars.

riirlh Ann. Itopl. Sute Mtoatalaftot, Ik 217. *BlevaiiUi Ceiuiu*, Uiaanl laduatrlM, p.4t.

Diyilizua by GoOgle

26 ooLD-qvAsnz ysub op hbtida cttt and cnuas TAUCOnr.

EaliwMUd pr$imam fptid in California.

11

Ss.5 Ii

ao

w 1

Twr.

Iw. 1S91.

Total

1.T6

1:J.8

Is

1S.S

The production of NAvada Gonnty prevkms to 1881, when the mates liy ( Oiinfif's was iiiidtTtiikcii ly the Mint, can be given only as a rough estimate. A. Delauo, a banker and tuiue owner of Grass Valley, IMwbably hotter conversant with the facts in question than anyone else, gave in 187;{ an estimate of as the output of Neviula County IVom 1S49 to 1872, which, from its rehitioii to the total trold product, seems very reasonable. P'rom 1873 to 1880 there was au average total gold production of 17 millions in the State, and nay estiiiinte the proiluctioii of Nevada County during the whole of thai* period to have heeii L'S.S millions.

Eilimated gold production of Serada i'vuntj), tS49 to JS:io, iMclu*irr,

Taar.

ix.'sl

Taar.

&amp;6 S

1S.Xs. 188U.

r4oUMi.

18B3

i8ei

ri

Total

StiU less aoeurate infimnatioit is there available for the prodnotion of the Nevada City and Orass TaUey diatriota, wbidi aivrays, however.

Diyilizua by GoOgle

ibmis tli iMgest putt of the sums oontribatlng to the total of Nevada

County. A very great amount was taken from the placpt s in thv first decade. It was estimated' that up tu .Tanuary, ISoo, $3,58G,0U() bad been proiluoed from the placer diggings iu the immediate vicinity uf Grass YaSSy, and many milUmis were also taken fVom the surface placer mint's of tho Nevada City district. The Shelby Flat and Ilrnsh Creek diggings have yielded several millions; the high gravels of Lost Qill, Wet Hill, and American Hill several more; the Manxaaita Ghannel about 3 millions. Mr. Delano estimates (lo<% cit.) the total product of the (Irass Valley district from lS4n to 1872 at 10 millions, and that of the Nevada City district to bo the same amount, which seems somewhat high when compared with the total estimated oatpitt of the county. Mr. William Ashburner estimates* the jtroduct of the quartz minus of Grass N'mUcv fo !h' Tiot less than 23 millions for the ]>eriod to to which uuiuunt Maiisachusetts Hill aloue contributed 7 millions; up to the present dato the Eareka-Idaho has produced over 17 millions, the Empire and the North .Star probably H millions each.

The exact information avaUable is very fragmentary; the production by individual mines has been reported in the Mint reports of 1889 to 1802, inclusive, the later reports giving production by county only.

The following data are obtainable for the gold and silver prodnetion :

Tear.

Omitii Valley diatrict. Id-

mm Flat

Neradji City diatrict. Id-

eliidluic Wll. Uw Vily.

Total.

wee..

a 500, 000 0 67,000

ijuarU miuoa omljr.

Do. Do. Do.

Only principal

)|ti!irt/ niincH. (Quartz m iuea only. All mine*. Do. Do. Do.

Only largo qaartz minea.

do

a2, 000, 000

i, -232 1. .'.14, WO 1,203,050 1.810000 1,1S0B0

18S8

Mint repiirt

do

do

l.(Wti,600 720730 864,600 781,250 840,400

Sapl.J.ItaaaSiinM,iW7,ih37.

28 OOLD-QUABTZ TEIK8 OF NETADA dTT XKD ORAffl VALLEY.

The pruUuctiuii of Grass Valley is derived almost exclusively from quarts mines. In the Nevadft City dittiiet tlie placer mineii still contribute

a sniall part of the product.

Accepting Delano's estimate for the earlier years of 8() million dollars for 1849 to 1872, tho estimate for the period 1873 to 1893, inclusive, woald be about 33 millions, or a total for the districts of aboat 113 which I am inclined to consider a very conservative amount rather too small. The qaartz mines have certainly contributed 60 per cent of this amount, and perhaps more.

It will sct'ii that the of Nevada County has at an average of 2 million dollars for the last ten years, also that Grass Valley daring the jiast ten years has produced an average of about $850,000 per year, and Nevada City an averaro of $400,000 per year.

In tho above data the gold and silver jiroductions are not the latter being comparatively iusigniticaut. The 31int rejMjrts give the production In vine, tiioagli the estimation of prodnotion by weight in ounces would, perhajis, be a better plan. The silver jtrnduct of Nevada County for 1804 and 1885 is given as about t40U, but it is apparent that the production In reality mnat be larger. Assnming a production of 50,()00 ounces of bullion 850 fine and containing 12.5 per cent silver, which probably is below tlif average, this liiillion would contain G,250 ounces of silver, and as several of the ores contain much nwesilTery this Talne is certainly a minimum. The average productloa is also geoeially above SOfiW onnoes of bullion.

Diyiiizea by

Ohaptbr 11.

Generai. Features.

The geoeral geologic features uf the region hero under discussion are delineated and deficribeil in the maps of the Gold Belt, especially on the Smartsvillc ami ( Olfax sheets, and to them the student dcsiroaeof more extended know the Sierra Nevada must be relcrred. It IS, however, desirable to iudicatu briedy the connection of the districts iMve described with the general stnietare of the sarroonding eonntry. Throoghoilt the Sierra Nevada there is nno sharp geologic distinction to be drawn. It is the difference between the older rocks — the bed-rock skies,'* as it is usually termed — on the one hand, and the superjacent ssries," or the nuich younger gravels, sands, clays, and volcanic rocks, on the other hand. The bed-rock series toiisist of liigbly altered sediuieutary rocks, crystalline schists, uitd older igneous rocks, on which the sapeijaoent series lies in approximately horisontal position. Tlie rocks of the former serii s have been subjected to orographic disturbances, and to a great extent have been compressed, broken, and crushed by these forces. The rocks which are now at the surface were once below it, probably thousands of feet; successive uplifts and eon staiif erosion have removed the ui>]>i'r [lars of tlic nx k masses and those once buried iu the fouudutiuus of tlie range. Kightly to understand the geology this fiiet must be borne in mind.

While it is eomparatively easy to unravel the later (Neocene) history of the Sierra Nevada, the same can not be said of the immeasurably

longer periods preceding it. They included sucressj ve epochs of quiet sediuientatioii, when the ocean covered the phu e where the range now rises; several distinct epochs of intense volcanic uctiuu, when the lavas built up mountains of igneous masses; and other epochs during wliich mountain liiiildiii;: forces lifted and crushed tojrefher sedimentary and igneous products, in these compressed and crushed masses occurred enormous abyssal intrasions of coarse-grained granitic rocks. Animal life, on the remains of which we depend for the identification of the sedimentary formationi, was unusually seatit duriu'r the intervals of dc'itositiou, or most of the fossils were destroyed during the metamorphism which the locks have undergone. Many parts of the Sierra Xevada have, indeed the aspect of pre Cambrian complexes — the oldest kuowu — thon$;1i, fVom the evidence available, it is certain that the rocks of the range in general are of much younger age.

The Bed-Rock Series.

80 Oold-Quabtz Tsins Of Nbtada City Amd 0Rab8 Tallbt.

Tbe 17evaclft Gfty and Graw Yallej district is located in the upper foothills, near tim line wlu-re tlnoM i{;iie<)U.s rm-ks of the footliill repon give place to the wide belt of slaty, sedimentary rocks of the middle range; east of this Kcdinieutary belt tbe granitic rocks of the highest partsof the range begin. High ridgesof fine-grained, dark-green rocks diabases, nnd augite poqihyrites form the rtrst footliills nf tho Siena Nevada iu Yuba and Nevaila counties. In the latter county these rocks extend to near Anthony House anil Indian Springs, where they are by u belt of i oarser-graiiied granitic rocks (graiioiliorite, diorite, and gabbro), which terminates along a line drawn by French Corral, Itough and Ready, and Wolf Greek Mountain. Eastward of this line, up to KevadaCity and Orasa Valley, the geology is very com* ple.v; telativelj' narrow belts of more or less iiietnmoi iilinscd seiHiiientary rocks, Ktaudiug at steep angles, alternate with large tjuuntities of fresh or metamorphosed igneous rocks. Near Nevada City this complex is from tlie predommaiiMy sedimentary slates to the east by tbe rounded southern end of tiiu great intrusive gruuodiorite mass extending more than 20 miles northward into Botte County.' In the southern part of Nevada Comity tbe diabases and porphyrites of the foothills evtciul vt iy far eastward, and an area of tliese rocks reaches nortiiward, iucludiug Osborne liill, to the eastof Grass Valley.

The rion of oompllcated stmeture begins at Rough and Ready, ff miles west of Grass Valley, with itinphibolites and gabbros; then fol lows a belt, from one-fourth of a mile to miles wide, of sedimentary clay-slates and siHoeons slates, which, near the North Star mine, enters the Grass \'alley traeC A branch of these slates is deflected to tlie southeast and traverses the northeastern part of the Grass Valley trac t. iJetween Grass Valley amd the main clay-siate belt lies a body of diabase and porphyrite about three-fourths of a mile wide, the continuation of which northward, though broken for a short distance by intervening slate masses, is found west uf Newtowu. East of this diahase belt liee the Grass Valley area of grasodiorite, 5 miles long, a rather narrow hotly of coarse-grained granitic rock, the northerly end of which is fountl in the city of Grass Valley. Kastward of this comes the great porphyrite and diabiisc area of Osborne Hill, limited again by the above-mentioned streak of sedimentary salsa cutting obliquely

across the Grass Vulley tract.

The greatest complication is found between Nevada City, Newtowu, and Grass Talley. Win tbis area the rocks nuiy be divided into three groups: (1) The two narrow of siliceous clay-slates with steep dip, one following the contact of the Nevada City gmuodiorite ai-ea for a long distance, tbe other embedded in {lorpbyrites oue-fonrth of a mile eastward. (2) The diabases and porphyrites, occupying a considerable' area to the sonth of Nevada City and cfnitinning down to tbe viciiiity of tbe Marylaud mine. These dark-green, tine-grained

The Mf.D-Rock Series.

rocks form pointed areas raouiag out northward. Tbo largest, adjoining the ftratnientiond slate belt, eomeii to ft point alMMtt 3 mfles

northwest of Nevada City. (3) Tbe diorite-gabbro-serpeutiiie j-omplex, beiunitig iiortli of South Vnb;i Hivcr. for!iiiri;r a Irntit nlar mass 9 miles long and not over 3 miles wide, and ruumng out in several loints short distance east of Grass Valley. The largest part of the latter area OODSlsfeS of .leoarsefrniiiHil. li<,'hternr darker jrreeti timid' or ;,'al)- broom arock intermediate het ween the two. In it lie lenticular masses of serpentine, usually running oat to sharp |Hints. The road from Nevada Citj' to N'ew crosses the two larjiest of these serpentine masses. Less altered pyroxenites and pcridotites are found in or near the serpentine. There is excellent reason for believing that all the rocks of this complex are of similar age and origin.

Turning to the question of the rehitions of ;ill tliesc difVerent rocks, it should be stated that no fossils have thus far been Ibund in the sedimentary rocks of the district. The greater part of the latter have been referred to the ('alaveras formation, which embra<'r's the Paleozoic sedimentary rocks of the Sierra Nevada. Among the Paleomic rocks the Carboniferous strata doubtless predominate, but the paucity of fossils has permitted identiUcation only at relatively fisw The detertiiination of the rocks m <|iiestion as " ('alavoras,** therefore, rests on circumstantial evidence only. These slates of the Calaveras formation ate probably the oldest rocks in the district.

Dnrinff a mountain biiildinjr disttn bailee toward the end of the Pal 02oic or the begiuuiug of the Mesozoic these beds became folded and compressed. This earliest uplift was associated with the outbreak of igneous rocks, which, indeed, in some localities took place even dating the deposition of the Carboniferous beds, but of those igneous rocks there is no positive trace iu the region under discussion. It is believeil that all of the igneous rocks of Qraas VaUey and Kevada City are pvobablynouo of them antedate the end of the Juratrias

During the last portion of the Juratrias ))cried a large part of the

Sierra Kevada was n land area. Part of it, however, was sii)>merged, and in that sea the latest sedimentary division of the bod rock series — the Mariposa beds — was deposited. These are black, carbonaceous days, intsrbedded in places with voleanie toflb, showing that during their formation volcanic forces were acting. In this district a narrow belt of black clay-slates, ioterstratitied with clastic volcanic material, has beea determined as belonging to the Mariposa beds.

After the IIanpo-a eiMich followed a time of the most intense moan* taio-bailding disturbance, accompanied by the outburst of an enonnoas qnantiiy of igneous material of different character and texture. The younger sedimentary rocks were folded and compressed and welded with the older series of the same kind, while intrusive masses were

Diyilizua by GoOgle

32 OOLD-tiUARTZ VKIN OF NEVADA CU V AND GKASS VALLEY.

injected iu tbem far the surface, aud volcanoes with thousands of feet of lavas aud ash niasseawere built ap on the surface along what we now the foothills of the nmge. The diabases and the porphyritea bolotijr to tlii-i volcanic pcriml, partly as surface flows and dikes, partly as deep-seated intrusive masses, consolidated as coarser granular rocks fiur below the snifue.

Finally, as the last and farthest-reaching phase of that period of igneous activity, came the intrusion of the large granodiorite masses iu the then deep-seated part of the range. This took place on so gigantic a scale that the mind atiiveB with difficulty to comprehend the mechanics of the ])rocesa. Thns. the {jranodiorites of Nevada (Mty and Grass Valley lue the most recent rocks uf the bed-rock series. Finally, alter the intrusions of the gianodioritei, dynamic forces, acting on the maas wiHi different intensity and in diflerent direction, pradooed fissure systems in which auriferous solutions ascended and deposited their contents. This forming of the mineral veins was the last phase of the Meeozoic revolution in the Sierra.

By no meaiLs all of the roclis of tlm distrirt are now in the same condition in which they were formed. Successive dynamic forces have acted on many of them, pfodndng deformation and achistose stmcture. Chemical forces liavc acted on them in ;it least tliicc distinct ways, changing their mineral constituents until their original form is sometimea soareety or not at all reeognizablefiTat, aa a result and concomitant of dynamic metamorphiamf second, by the heat and mineralizing exhalations of the intnisive pranodiorite; third, by the action of the hot auriferous solutions uu the rocks adjoining the Assures through which they drcnlated. Often several or aJI of these effects have been combined in one localit w rendering very diflicult the ta-sk of unraveling the changes through which the rock has passed, iu the region covered by the Smartsvflle sheet, in which the larger ]>art of the ntcft described in this folio is tliere has been less of that intense dynamic action slaty and -rbi-Jtose structnre by compression than ill parts uf the Gold Belt tarther south. One hue along which the racks have been cmshed and rendered schistose extends in a iiorfberly ilirectinn through nearly the whole region, and pjisse.s some distance beyond the western boundary uf the Gi-ass Valley tract. As in certain localities along that Hue the granodiorite has been rendered schLstose, it follows that this line of disturbance was produc<'<I later than tbe inti nsion of grnnixliorite. Another line of schistose structure iu the Culuveraa furmatiou the granodiorite contact south and west of Nevada Oity. Bat most of tbe rocks in the area of the special maps are oi massive character.

Thb Bopbrjacbiit 8Bribs.

At the beginning of the Keooene period the Sierra Nevada formed a moontaiu range of sabstantiaUy the same outlines as that of to-day,

Diyilizua by GoOgle

U!Idomsv.|

THE SBSIEa

bat of much lesA lieight, the siuiiinits — alon the same linens tlu' present ones — having; an elevation prohahlv of hunt 5,0tH) feet, ill latitude .ib" 3ii. The range had been above water sure the end uf the Junitrias period, and in its lower part long-ooutinoed eroidon bad reduced it t4> a hilly, tindulattUg country, frequently hrokeii by higb ridges aud iiiolated peakii. A drainage ttyHtiHn Mjmewhat tiuiilaito tlie one of the preaent day had been developed, and anrifiBrona gravels accumulateil along the streams from the d''bris of the numerous quartz veins. Tlie -itreain reeeivinj; the drsiinaire of tirass N'alley ami Nevada City torrespouded closely to the Kiver, bat ulao eiubniced the waterriied of the upper Bear River. Its mntbem branoh came down from Dutc li Flat and You Bet with a northerly liireetion, eiDssiiii; Deer Creeli ut Scotts I'lut and the South Yuba at Blue Tent; then turned westward and flowed down to tdie Great Valley by Biulger Hill. North San Joan, French Corral, and Smiartsville, During the latter part of the Neoeene pericKl volmnie eruptions betraii iieai" the siimtnit of the Sierra Nevmla, and luaHMe.s of volcauiiluaterial began to iMiur down the river channels. The flrst material empted was the light-eolored,

8iliceon rock called which was of comparatively small nme, cuutiniug itself as a rule to the river channels. The larger qnautity of the emptives poured onfe as volcanic mads, which easily fimud their way down to the foot of the range. On the lower slopes they became mixed with more or less gravel and sand, and their eruptive character is now less appai'ent. Very heavy tlows of this kind found their way down the old Sontb Fork of the Yuba, and part of them tloodcil a low divide and the Nevada City basin. After a short interval, during which considerable erosion took place, the so-called "cement channels" or 'channels of the volcanic period'* were formed in certain part.s of the Sierra, wherever erosion cut through the rhyohtie tlows. No such channels have been found in the district here described. Then the period of andesitic eruptions began, and mud flows again poured down from the vents near the divide, at first as dark fine tntts and sands, later as a }jray or brown fiittaceous breccia, coutaiuuig, in the tbothills as well us iu the high range, larger, more or less angular bowlders of the dark-colored porphyritic rock called andesitv. These last flows, coming down in raiiid succession, flooded everything aud covered up the middle to such an extent that only isolated ridges and peaks protruded ab*ive theui. The whole area here considered was thus once a gently sloping lava tield, above which only Banner and Osborne hills piotriided. The last of the andesitic tlows is to mark the close of the Neocene period. During the vulcanic epoch the Sierra Nevada was snbjeted to a tilting uplift, which at the .summit probably amoaiited to several tlumsaiid feet, aud the streams at once liegan the work of cutting into this de.isolate lava plateau. The dixeethma tHu took were more generally transverse than fiirmerly. Their similarity to the tM drainage was caused IT OBOL, FT 2 3

Diyilizua by GoOgle

34 GOLD-QVARTZ TEtMB OF NEVADA CITY AND ORAflS VALLBT.

by protruding ridges of bed rtxk, which in many place* confined tlie new j-ivcr to t he old valley. This work of canyon cutting has been continued with energy uulil tlie pieiieut time. Nut only lias ma6h of tiie finormouB lavs muns been wadied away, but, owing to tlie iiplin. tlie livers li:ive rut down far below the old bedrock surtuue and created the characteristic features of the Sierra Nevada of to-day. Tfaeee are deep, abrupt canyons separated by broad or narrow ridges of more gently undulating Hiirface.

Ill the <listrii't desiTibed in this folio the sloping ridges — Marmony liidge and the Banner Qill-Towutalk Uidge — are the only remnants of the lava sheet which once covered nearly the whcde region while tlie present \v:itereoiirses. here wholly unlike then Neocene predecessotSi are sunk several huudred feet below the Neocene surface. Between ttie close of the andesltic emptioas and the present day ooenrred the extensive glaciation of the High Sierra, but the glaciers terminated about 3U miles above Nevada City ; and it may be stated with certainty that neither in the Neocene uur iu the I'leistooene period have any ioe tnana extended as fiir down aa the latter place.

Diyilizua by GoOgle

CHAPTBB iH.

THK lONBOUS ROCKS OF TUB BED-ROCK 8BRIESS.

ORAHODIORITB. PBFINITIOir OF BOCK.

riidi T th' iiHint' granodiorili' are coarsely f,'ramilar rockB, uiul at depths below tlie Hiirface, having a iioniml grauitic (eu grauitic) structure, and a uiiueralogical oomimsition of quartz, 8od'1iiiie fidpara, orthoclafle, hornblendA, aod nearly always biotite. Titaiiito and that;iietite are always present accessory coustitueuts. This ruck, which iu the Sierra occurs in enormous areaa, fomM an iiitennedfate group between the qoartzmica diorite,s and the granites, bein;, however, more closely allied to the quartz-mica diorite than to the granite. Oomparieou of numerous aoalyaea ttom various parts of the Sierra Nevada Hbowa that the chemical eoDkpoatdon varies between that of a quartz'mica-diorite and a qnartz-monzonito (adainellite, banatite, Hriifper). Its Kolofiieal occurrence and in general entirely similar habit preclude the possibility of dividing ft into aabgronpa.

The rock is very characteristic and can not easily be mistaken. The feldspars are generally white; the quartz is not very conspicuous and does not oeeor in large grains, as in some granites of the high Sierra; the hornblende is dark-green, often in long, rough iirisma; the biotite is of tlie usual dark-brown color. The general eflTect is a lighi'grayiah color.

SiO...

CaO.. MgO.

K,0..

59 to68i U to 17 11 to 2i 3 to 61 I tosSi to :n I 21 to 41

f'tT crnt

Diyilizua by GoQgle

36 Uolu-Quastz Veins Of Nevada City Akd Gkass Valley.

City Abba.

Extent and character of tuvfaee.— The Nevada City tn"anodiorit urea forms the southern end of a prcat massif extending northward far up iu lUitte County. It is generally sharply defined in this region, but in its northern part more basic diofitM and gabbroB are intimately con- Bei ted vitli it transition.

The rock oi-cupies a largo part of the area covered by the Batiuer Hill and Nevada Oity sheets. It forms a aeries of rounded, eompvratively gently liills with elevations gradually increasing eastward, liver Creek crosses the area in a canyon which, south of Willow Valley, near tbe contact with the sedimentary area, has precipitous and narrow dopes and is t r TOO feet deep. In the western nurse it has mora gently sloiiing sidt-s, tlie indiniition rarely exceeding IL'' ; a ste'per i.s, however, usually noted ininiediately at thu creek, in places Ibrming almost a "canyon within a valley." Little Deer Greek cnts a smaller canyon in the granodiurite farther south.

From Nevada City tu the i'ruvideuoe uiiae tbe caqyou, cut iu less dtointegrated rook than fivther east, is itanow and roeky. Hie veateni and southern ]iartof the area i.s rather gently hilly and nndnlatini;, bat is cut near Deer Ci cek by steep ravines.

MacroHcopical description. — The normal grauodionttf is a fresh, coarsely granular rock of light-grayish color, composed of dark-green bomblende, dark -brown biotite, colorless (jtiartz, and white or slightly yellowish feldspar. The grains average about 2 or 3 mm. in diameter. The hornblende is relatively more abundant titan the biotite; both of them stmietimes occur in idiomorphic form, the hornblende as thick prisms up to Id mm. in length, tJie mica as liexagona! foils up to .'{or 4 nnn. iu diameter. Small grains of yellow titanite are sometimes noticeable. Pyiite is, on the whole, rare, and ooenrs only In small grains ootineeted with the hornblende. Copper pyrites have also been noticed in the horn blende, but pyrrhotite iloes not seem to occur. Near the eontaetjs the hornblende sometimes, though by no means always, increases, giving the rock a more basic aspect. Such is the rock along the conta<-t from Deer Creek northward, and also in the vicinity of the North Banner mine, where it should more proierIy be called a diorite. The dark shots so frequently seen in granitic rocks abound in certain parts of the area, and are coinjiosed priiK'ipally of feldspar and hornblende; tliey often dlOW tissues and breaks tilled with granudiorite. On the whole, the inrattodiorite shows but slight variation iu the diflRnent parts of the area. The outcrops of the less deoonposed rock are smooth and rounded.

Mieroscttpicttl description. — In thin sections the fresh, unaltered chariicter of the rock, compBied with others of tlie tlistrict, is very striking. Ttie character is comparatively uniform. The mica is normal, darkbrown biotite, with small though distinct angle between the optical

Diyiiized by

Obakodiobitb Op Netaoa Ciit Abba.

Axes; the color is a clear vt'llowish-browii, without any Hliade of red. It is coiiii'times iiliotnorphir. Ln<'al alt'nitioii Iins in jtlnces converted soiue of it to cUlonte ur inusrovito, butli an inserted parallel plates. Smal] fragments of a doabtfiil mineral are In one slide inter- {rrmvii with tlie biottte, sliowinLr hliuand yellow plcorliroisni and aii extiQc-tiou of iibont 45. Tliu liorublende in green or brownish-green and oompact, sometimes roughly idiomorphie and with a maximum extinction of 18" to 20'''; occasionally a little chlorite and accompanies it. The hornblende sonietinies incloses foils of hiotite. but is also occasionally .surrounded by biotite. lu one specimen 300 ftet from the contact in Deer Creek the hornblende shows sharply defined kernels nt" ant,nfc.

The predomiuutiug feldspar is forming usually roughly idiomorphie prisms with strong twin-strlation and eomparattvely low symmetrical extinction, hardly ever above 20". A zonal structure is not common. A micaceous mineral occurs in some as products of incipient decomposition.

The ortboclase is less abundant and occurs as irregular grains; it sonietinies contains a slifjlit iiiicro])eithitic ofalbite; rarely some grains show a very tine aud indistinct striation, suggesting ttie presence of anorthoclase. Mlcroeline does not appear to be present. The quartz forms irregular p-ains ; nndulous extinction is seldom notice* able, uor is there on the whole much evidence of strong dynamic action on the rock.

Of aeoessory minerals, magnetite in irregular, often rounded grains

ia always pn'sent and mostly contained in tlic lioniblt iHir or in the biotite. Iron pyritu is sometimes seen; it is never beyond doubt primary, but alwajrs appears associated with the deoompoeltlon products of tlu! lioriililciHle. Titaiiitc ia coiiiiiioii, as well as apatite and survtm. The structure is characteristically hypidiomorphie; the mica and hornblende are sometimes, the plagioclaso nearly always, jiartly idiomorphie; these minerals are cemented, so to by a later ooasolidated mass of orthix-lase and quartz. This structure is always characteristic of the Small crystals of plagioclase are occasionally embedded in the mica or In the hornblende. In some 8pe<:iniens a very fitio fjraiiied micro pcgniatitic iiiteigrowth of quartz aud ]dagioclase is noted as a rim surrounding the end of some of the feldspar erystiib.

An important characteristi<- of the granodiorite is its fresh charac* ter, owing to an aliseneeof dynaniira! and clieniical alteration.

The dark .spots ta-curring so frequently, tor insLance at theqnarry at the west edge of the Banner Hill sheet, consist mainly of homblaide (with a little mica) and idiomorphie ]ila;jrioi lase, between the prisms of which lies a little quartz. They also contain much magnetite, and a grain of probably primary pyrite was onee noted.

88 TBINB OY ITBTASA dTT AMD OBAaS VALLEY.

Okemical compoKition. — A fresU Bpcciiuen taken near ShurtIeft''H barn, about 1 mile Rdiitheast from Nevada City analyzed by Dr. W. F. Hille* brand, gave the lollowin insult:

Analyti* of granodiorite from near Srrada ri/y.

t .38

j 1.M

' 2.36

' .10

j 4.5S

8rO ! Them.

BaO ' ,07

K,0 1 2.

Na.O 3.40

LiiU I True*?.

8iO,..

TiO . A1,0, Feo.. MdO .

P*Or.

Iw,

The analysis typical of the nnodiorite. The relativeJy low percentage of MgO (FeO, I'V/Oj) and i-< cliaracteristie, as flic fact tbat the suiu uf the alkalia exceeds considerably the lime. The TiUj is pwMcnt cUeily m titanlte. In view of the ihefe that the wnMst eoni- ])osition of the hornblciubi and mica is unknown, there are not sufficient data for the calcolatiou of the ooustitaeuts of the rock. The ruck coutaiiia in esthaate:

r-

' IVr cent.

KAlSi0. ir.

C*Al.SiiO, ! 15

Horablande aod biotit* 16

Quartz . ... Apatite ... MafiMito. Titmilt

S2

.it* 1.S0

1

Diyilizua by GoOgle

Ukanouk&#x27;Iutk Of Nevada City Area.

Tbe |>lugioeJae is vouaetiueutly au oligoclase. It sliould be remarked that til* Tdliitioii between the potassa and the soda, by no means ooustaut. la a spec-iineii Trum tlie same area, taken wlifrethe PordoilS

load toss's iJm-k Creek, 1 miles north of Nevadii City, a partial analysis by \V. li. Melville gave U.80 ceut KA) and 4.25 per ceut Na,0.

graiioiliurite very bofb aud de<-omiHi8ed ; iu places the deuoiupusitioa reacbeB a depth of SOO feet. Espettially is this the ease in the eastern partof the area, which is covered by u deep dark red noil iu vhieh few remaining harder bowlders lie scattered. This i.s a trne residual sail, derivetl from decomposition in place, and readies its greatest depth on the northern of the rides. Beautiful exposures of this decom- [►ositiou are seen in the liyilraiilic jiits soutlmast of Canada mil. The decouiiMMiition of the grauodiorite seems to have at least two distinct stages. The first consists in loosening the grains to a soft emmbling ag;create. This loosening seems to he due mainly to the decoinpositiou of the feldspar grains. The biotite aud hornblende are not much altered. Snch fa the condition of the rook in the lower Ibothilla. The second stage consists in the decomposition of the and biotite as well as the Next to the ipiartz, the biotite is the most resistant uiinural. Tlic ferrous oxides are completely converted into ferric, and the resntt is a soft, olay, deepred materbd.

In the western of the area niosr the residual soil covering the ground has been swept away; coarse, crumbling, aud yellowish rock very frequently comes to the snrfhce, and harder masses flequeutly show their light-gray, round outcrops through the more decomposed snnrounding nwk. Tins pwuliar manner of is w-Il shown iu several places. The harder niu8.ses are often surrounded by concentric softer shells, as seen near the nilroad station at Nevada City. Kxcellent exposures of very hard, rounded oiiterops in nantly soft rock are seen on the bed rock of the hydraulic diggings half a mile northwest of Nevada City, and similw sharply dellned hard masses, usually called "bowlders," are often found in driving ton* nels through the soft decomposed grauodiorite to reach the Tertiary channels.

£Mtkm to awnntmiihig yvdbtThe gfaoodiorite is the yooiest

member of the fundamental .series, little affected by inechanical and chemical changes. It was evidently intruded far below the surface as immense masses or batholites of molten magma, which slowly consolidated and which a long-continued erosion finally ex])osMl. The rocks near the contacts, chiefly the rocks, show a most decide><l and characteristic contact metamorpbism, produced by the heat aud emanations of the eruption. The contacts are not gMwraUy well on act-onnt of the surfax'c : good ox poBOrSS ate however-, found on both sides of the massif iu Deer Ci-eek.

Diyilizua by GoOgle

40 GOUD-QUARTZ yEIN8 OF NEVADA CITY AND ORA88 VALLEY.

Dikes of graaodiorite iiocar sparingly in the adjoining wdinentaiy

rocks. One', iilMiuf fe4-t wide, wiis imtod in tlio twd tif Depp rm'k..Sl) feeteiMt of Ibti contact; tbis rock is u uoiiuai ;;raiiMhuiit, voiitiiiuiiig fhigments of the Redimentary metamorpbio roclcs tbrougli which it breakH out. In tlie F'di'riil Loan niin', dikes of dark dionle, with large hornblende crystaU, break tbrougb tbe sedinipiitsiry ro<;k.s; these diorites, irhicb coutttin some pynte and pyrrhotite, are probably getietioally oonuected with tlie granodiorite. At the ditch 400 fiset above and sontln-ast of the initM' tlic iramxliorit*' sends nnt dikes or of sumcwhut darker dioritiirhaiaeter. A great ituniber of dikeh or smaller intnisive masses are noted atiove the North Banner mine at the h'ad of T.ittle Creek; these consist of ttsnally rather dark granfHlioritu or tinartz-mit-a diorite.

A small, apparently intrusive mass on the Beotts Flat road at the divide north of the Feleral I/Oaii, and the small like nearest tO the lit it'l ot' Little Creek, lunc been indicaterl as diorile on the niiip. They present, however, souje ie;uliar features, and show great similarity with a rock collected at the extreme edge of the Banner Hill tract, on the road east southeast of IJantier Hill. It is believed that these nx ks should rather he referred t4 tbe later series of diabiisee and iHirphyrites, which IVeipiently carry hornblende.

An excellent instance of a small branching dike of graiiodiorite is seen on the south bank of Deer ('re<*k Ik'Iow the Providenee mill; other dikes occur uloug tbe road, just south of the same null and on the south bank of Deer Credc 400 ftet west of it. Intnisive masses of granodiorite

in altered diabase are also .seen in the I*rovidence mine on the si.Nth level, on the conUict vein, and on tbe third level of the Nevada City mine in the seooud crosHcut in the fttot wall south ftom the new shaft.

Dtoritic J'alien. — In the vicinity of tbe North banner mine the granodiorite becomes more basic and similar to a diorite. At tbe contact a ftw hundred feet southwest of tbe mine it also assumes a finer grain. The small area northeast of the mine inclose*! between the andesitic bnMK-ia and tbe sedimentary rocks is a ratiicr dark quart/.-niica-diorite. Ill the area west of the mine, separated flrom the former by a prqcting tontine of slate, the ruck is clearly dioritic and consists of plagioclase and brownish-green hornblende, one of the latter showing a kernel of aufrite. A little quarts separates the lath-shajied feldspar crystals.

Dioriti' (iiiil (/niiKidii'iih- iKirtlnrrsf of tin' Xirmlft Citii viiiir. — Near the contacts the graiiodiorite has sometimes, as noted, a tendency toward more basic development but no extensive change of this kind

occurs untilbeyoinl tbe Nevada City mine. From Hir<'bville. (! miles to the northwest, to tbe Nevada City mine the graiiodiorite is atoiued by an area of diorite, with associated gabbros and pyroxenitee. At the excellent exposures in Shady Creek, about 2j miles east -northeast of Frenoh Coiral, the contact bMween diorite and granodiorite is dear and

flKANUUlOKITL UK UUAS8 VALLEY ABEA.

Hliarp, the latter heiiij: yuiuiger and iiitrnsivp into fonnpr. Afjain, in tii cauyou of tbe iSoutb Yuba tbe costa<-t between the two tbrinu tioDB ia sharp, thongli it appeara to be a ttmlt plane dipping east; but from rlio riv"r to th Nevada City iniii*' llii' relations are doubtful. Along a line running <iue northwest from the mine the gi*au(>diorite becomes darker, and change-s ini|)eTCeptibly into dark diorite and gabbro, replaced pyroxcnite at the edge of tbe Nevada City tnwt. Tims tht rr is along this line no distiin t contact line to be drawn between the grunodiorite on one liaud and the diurite-gabbropyrozenite complex on the other. Thia ia puaslinp, for all the <ther evidence is in favor of the latter being distinctly older than the granodioriteK; besides, it contains dikea uf tbe series, wbieh, on tbe other hand, is diatinetly older than the granodiorite. There niy, after all, be a contact, although the similarity of the formations and tlif of tin-surface pn vpiit its b'ing noticed.

The diuritr tlikts near Indian Flat.— lu the belt of the schistose greenstones 1,000 to 2,000 feet west of the granodlorito contact there are two long-drawn bodies of diorite which appear to be intrusive masses; they probably are connettcjl with the granodiorite in origin, and form a facies or product of differentiation of that magma. Iie rock is dark and coarse, and composed of dark-green uraliticappearing hornblende and white or greenish feldspar. In thin section large grains of green hornblende and partly idioniorphic plagioclaie form the ehief conatitaents. There is much apatite and Umenite. Some of the hornblende may Ikivc been <Ierivcd fMU ajwiutty pyroxene, hnt of this tliere is no direct proof. A little seooodaiy biotito is noticed in the hornblende.

Cjka8S Vali.E Ak£A.

Edtint and clutrartfr i>/ nur/arf. — TImrranodiorit* of Grass \'alley forms an elongated area much smaller than that ot Nevada City, and extending along Wolf Creek for 5 miles south of Chram Valley. Ito

wiilrli varies tVdin less than half a mile np f( nearly 2 miles. A series of rounded lulls murks the area on both sides of tbe more abrupt canyon Of Wolf Oreek. Compared with the great mass of Osborne HiU, the area marks a depreKsimi of old Tertiary date, pvodaoed by the more easily disintegrating ehara of the rock.

Rock Gras.s Valley granodiorite differs somewhat in appearance from that of Nevada City. It is a greenish-gray, mediumgrained rock, consisting ot two kinds of feldspar — pale red and greenish— black hornblende, and 4uartz. Only e.\eeptioDally, as at the Scotia shaftt does biotito enter into tbe composition. Smidl grains of pyrito are not uncomiBon. The type is practically constant ovw the whole area.

Under tlio the plagioelase is either predominant, usually partly idioouHrphfc, and often lilled with mieaceom minerals. The

42 aOLD-<jUASTZ VEINS OF NEVADA CITY AND 0UA8S VALLE7.

ortlioflasp Irardly ever sliows rvstal niitliiH's, and is {jciierally frcslier tbau tbe plugiuclune. Tliu quartz is Konietiiiies iiitergrowii with the offtbodMe in mieropegtnatitic Btnietnre. Mieraperthite la also noted* and occasionally a very fliiely Btrintcd feldspar associated witb the ortliocln.4e, )>ossibly anortboclase. The hornblende is the ordinary granitic variety with brownish-green color, converted into chlorite and eptdote. Aooessories are magnetite, titanlte, ciroon, and apatite. The Krst mentioned mineral is somewhat titaniferons, for leucuxeno (titanite) has bccu observed to form from it. Small grains and crjrstalii of pjrrite freqnentiy occur, bnt are probably all leeondary. They are closely associated with the hornblende and sometimes surrounded by a chlorite rim.

The structure is typically hypidiomorphic, imperitet priams of plagloelaae and hornblende being partly embedded in orthoelaae and nincli (pmrtz.

Tbe rui-k on the whole is somewhat less fresh thau the granodiorite of Vevada City. Darker dioritic modiAcationa of tbe rock are rare, bnt were noted la the branch of the area found miles west of GraM

Valley.

CompoBitkm.— The analysis by Dr. W. F. Hillebraud of au apparently fteah apedmen from Kate Hayea Hill, near the Heda abaft, gave:

IVr rtmi.

SiO. 63.85

TiO: .5H

AkOi W.M

MaO OJ

CaO 4.76

SrO Trace.

iiiio ,e

MgO -'.07 i

K.0 3.08

Nx-O S.

LWO Tmm.

HtOlMlowllOoC 2H

llOabaTlurO I.W

FaA, .04

.W

Totsi I m.

Diyilizua by GoOgle

r.] OSAHODIOBITB OF GRASS TALLET ABSA. 43

The oomparatlTely simple composition reodera a csloalatkm of AiB

analysis possible, under the well-founded auppositiall that the horn* blende is of the ordinary alumiaoaa chacaetor.

8.S

SiO...

8iO,. .

A1;0,.

FeO..

Fe,0,

A1,0,.

MgO.

S.1

U.1

Quart/

Apatite

Total

The lioiniblende woalil then have the following approximate oompo> ritlon:

Fe,0,

FeO.. CaO . MbO.

1&7

U.9

Is.1 1S.6

Total.

44 OOLD-yl ARTZ VKINS OF NEVADA CITV AND 0KA8S VALLEY.

The lias tlio nniipositioii of an oligoclaae, which OOITO- HIMiiiUs with the

It in evident tkiit there is conKiderabte variation in the alkalia, for a partial analysis of the nx k from Allison's ranch, ratlier rich in liorii blende, by W. il. Melvillu, gave G.IG per cent CaO, U.5.'i KtO, X74 Nii,0, probably oorreHponding to 30 per eent Ab, 15 per cent An, and 3 per cent Or, or :i normal <|n:irt/. diorite.

Wcallicrino. — Tlion<;li similar to flie Cils" nx'k in ion and Ki'iii') develops a consnU'raljiy greater resistauce to weathering. It forms lightHMtkNred, ronndel onteroim, bnt leas chnraeteristic than those of Nevada City : nor does the disinti rrat iini extend down so dee] by far as in the Nevada City area. The extrcmu result of weatherinir is a deep-red clayey soil, a few fioet deep.

ReUttion to Hurrounding rockt. — While the gniuodiorite is singularly free from dikes and intrusive mnases, dikes of it oec-ur in the Kurrounding rocks, showing its more recent age. The contacts are satisfactory only at taoiated places, on aocoant of extensive weathering, bnt whenever Wi ll "\])osed are slinrji and ilistinct. On the north the granodiorite borders against the sedimentary rocks with distinct, tkuugb not wide, eontnetroetamorphic zone. A dike-like niasH of granodiorite with nnsati8fa<"tory is -ontiiiiied in the sedimentary series onehalf niilf west of the railronil station. The eontiK't with the siliceous chert in tlie sontliwest part of the area is very poorly esjiosed, but does not give the impression of very intense eoiitaet aMtanmrphinn.

The diabase and porphyrite near the contact are not appreciably altereil by the granodiorite, as fresh diabase wuurs close up to or immediately at the contact Dikes of granodiorite in the latter rock were noted at the old Peabody shaft, in Wolf Cre<'k, a little above the (iranite Hill mine, in the tnnnel feet south of Central North Star shaft, in an outcrop in the swampy meadow 2,300 feet south of North Star shaft, and less well expoeed at several points along the contact south of the W. Y. O. D. mine.

Aplite.

liefinitum. — Aplite is here used to desi<,'nate graiudar to fine-granular acid rocks, chietly consisting of alkali feldspar and iptartz, and usually occurring m dikes or dike-like masses in or near the larger bodies of granitic rocks.

Oeeurreneeii and deHcription, — A small, 10-inch-wide vein of coarse pegmatite crops out along the road 200 ftet north of the Mountaineer

mint'. On the Excelsior ditch, about 1 mile above Jones Har and about 4 miles from Nevada City, there is, in granodiorite, a dike 3 to 4 feet wide, of a medinm-grained white or yellowish rock, oonsistingof feldspar and quartz, with a very little bnwn mica. This rock (220 N. O.) contains l.dti ]er rent CaO. .'u K..O, and 'J.'l.'J NaO, according to a partial analysis by Mr. Gextrge Steigor, and is thus a graiutic dike rock with predominating alkali fieldspars.

Diyilizua by GoOgle

Ai&#x27;Lite.

In tlio northwestern part of tbe Nevada City txct there in, in diorite, aiarg< mass of this rock raniiing oat in iiuineroiiH brativhing dikes. Tbe8 little likes, intruded in the dark amphibolitic rock, are well wiu'i*' Ikock Cn-ek tin-eastTn liiiiitof the upliti'. The rock is almost white, luedtuui-graiuc-d, ut a sugary texture, and tains only a fow small grains of biotite or hornblende. At the sonthem end of tlie area it lias n sniin wliat scliistnsc uv iirosscd appraranop. Tlie rocks ut' this area have been subjected to dynamic action, nKtssibly a dinct result of the strains daring the ibrmation of the vein flsaorea, and tbongh schistose structure is not always visible, the microaoope reveals itscruslu'd rondirion. It is cssfiitially a nearly allotriomorphic interlaced, granular agaegate ut' quart/, and leidspar, except for a few scattered foils of brown utica and grains of epidote. Th quarts grainB are usually crushed and pressed out to long-drawn ajgrogatesj the feldspar <;rains show this to a smaller extent. Between the larger feldspar {grains there are many aniall ones, occasionally with nicropeg- Miatitic structure, and sometimee giving theiniiiression of having been producwl by crushiujr. Micropertliitic intergrowtlia are extremely common ; there is also some niicrocline. A few of the grains abow distinct twin lanMlfae, bat soine grains otherwise resembling ortbO' clase have an cxtKMnfly fine ami hardly visible striation in one direction and may Ijo anurthtK-lase. A partial analysis of No. loi) N. C. by Mr. H. W. Btokes gave 77.05 per cent SiOt, 0.73 OaO, 5.06 and 4- 3.1.'5 Na..(). The close agreement with the rock from Kxcelsioiditch should noted. The aplite dike, feet alj<>ve the Champion mill, is very similar to the rock just described, ttiounh not quite so much pressed.

Dt'Jinitioii. — The granite-porphyries are holucrystalliue, porphyritic ' dike rocks, rich in free silica and characterised by the prevalence of

alkali

(Jcfurrrncr and description. — Certain rocks occurring as dikes in the diabase near the granodiorite contact, chietly in the vicinity of the Omaha nnue, Grass Valley tract, belong to this group. The somedmeB very tim- 'raim d jrroundniass cursed them tn be laid tm the map asqum'tz itorphyries; but as they are true dike rocks, closely connected with granitic intmaiona, the name 'granite-pcwpliyiy" is more appropriate. These nn-ks differ oidy structurally from the aplites.

The granite-porphyries are chietly yellowish-gray or g'ay, tine-grained or flinty rocks, indistinctly porphyritic by smalt feldsiiar or qnarta erystala ranging np to 3 mm. in siie. Small foils of biotite are sonietini

Cfl present.

, .several types are pre-sent. No. 113 (1. V., from the priddpal torn, eontaiDs idiomoriAie, short and thick feldspar crystals, at least half of them with twin stristion. Phenoorjrata of clear quarts

Granite-Porphyry.

qnuta-porpbyrjr nwii.

46 Gold-Quaktz Veins Of Kevada City Axd Grass Valley.

with currodeil outlines ure White mica aud some epidote has formed in the feldspars. The biotito foils are oouverteil into epidote- eUorito aggregates.

'Dw groiiiidmnss is iiiicrocrystiilline, of iiiterlix kiiiu: fxrains of quartz and uuatriated fddspar ; si1.ho tiouie with twin In the gTonndmass shows micropegfmatitio intergrowth, approaching sphenilitic forms. Small foil of biotite occur in the gromidiiian.

▲ partial anatysis by Mr. George Steigar gavo—

CaO Ka,0

4.M

a. 88

or practically equal quantities uf Or aud Ab. Another rock from a smaller dik (109 O.V.) is yenowish-gray flnegrained

, but not flinty. Undar tlif' mirmscopc it is a splicriilitic aLr;;regate of feldspar aud quartz, the spherulites ranging front an iutimato intergrowth to typical radial aggregates, showing the htecdt cross between crossed nicols. The groundmass between the sphernlitos is tine-<:raiTu'<|. allot riomor])hic, )>nrt1y also miCTOpegllUltftic. A partial aualysis by Mr. George iSteiger gave—

showing thin rock tu be practically identical with the one lirst described. SiOt was not determined, but the rock is very add.

A third tyiM*, a dike in diabase from thefoorteenth level of the Omaha mine, near the shaft, is grayish, flinty, and shows small fi'ldspar crystals. Under the the feldspar pheuocrysts are very nuu li tilled with nieaoeons aggregates, cloning them completely. The gronndmass is a clear allotrinniorphio aggregate of quartz and nnstriatsd feldspar, easily resolved by objective No. 7 (Hartnack).

Similar rocks are also found in the diabase near the contact in the W.T.O. I), mine. White dikes, either qnarts*porphyries or aplites, are thofM on Little Wolf Creek. 06() feet south-soutlioast of the Golden Treasure shaft and in the new Peabody shaft Both uf these contain abundant pyrite, possibly introduced by the vein solutions.

uxuiWiN.) IGNEOUS FiOCKS OK THK BKD-KOCK 8KKUE&

Dioritb-Pqrphyritb.

Occurrenrcit anil ilesiription. — Tbt' ;ri ntuKltoritc Ix'iii;, flic liiti'st principal member of the fuutlameutal serieit, ver-few UikeH uf uuy kiud are fbnnd in it. The apUtes have already been arantioiied, and the granite-porphyriea in nil probability stre also later, though not found in the granodiorite. Iti thref"; phiccs basic dark -green iMrphyritic rocks have also been fuuuU as dikes iu grauodioritc. There may be more occurrences of the same rock as dikes in other parts of tbe fiindamental series, but if not prominent tliev would esvsilybc ovorlookod, as they present great similarity tu the ordinary liornblende-porphyrites.

The beet exposnre, to vrhich Mr. George A. Treadwell called my attention, is in the canyon of the South Yuba River, SOO feet below the iixccLsior dam, about northwest of Nevada City and 2 miles outside of the special sheets. At this place there are two dikes 10 inches wide in the normal granodiorite, only a few feet apart; both dip W., and many fissures jniiits w itli tho sMnio dip arc w'on in the vicinity. The ruck is dark-jjreeu uud dense, with many small feldspar crystals and abundant aeicnlar black hornblende. In thin section tha rock Is seen to be liolocrystalline iKjrphyritic; the larpcr feldspar crystals are uot over 1 mm. long, while the ueedlO'Shaped hornblende may reach 24Mr3mm. The former are sharply idiomorphie and show twin atriapale greenish-brown in color and with normal extinction. The pronndinasa is composeil of inierolitea and {grains of tlie Hame horn blende, and apparently also the same plagioclase, as there are all transitions between the phenooryats and tlie microlites in the gronndnnuss

. Miifjiietite is rather abnndaiit. According to a determination by Mr. (ieore iSteiger, the rock contains (K>.s.j ier cent HiOf The rock hows the character of the lamprophyrie dike rooks, and is closely related to the camptonites. t1iou{;h not BO basic. Su(;h dike rocks have been found, though not abundantly, in various parts of the iSierra Nevada, and are apparently always later tiiau tlie granodiorite.' They often appear paralM to the gold-qnarts veins, and have evidently been inieet<'d a short time ]irevions to the formation of the latter. Two localities have been found iu the Banner Hill tract, but in both cases tbe rocks are so altered as to be scarcely recognisable. The Urst is a dark grayish-green roi-k found on fha dnmp of the Independence shaft (Murchie mine), and is said to have come from a dike running parallel to the vein, which dips W. 3C°. In thin section it is seen to be a very mnch altered porphyritie rock, wiHi long, slender hornblende needles, now entirely etni verted tocaleite. The second occurrence forms a 3 footwide dike in the Alpine tunnel, forming the haugiug of the &t. Louis vein. The rock has nraoh tbe same extremely decomposed appearance as that tfom the former locality, and shows small hornblende prisms in a ground mass of line ftlted mixture of feldajiar microlites and acicolar hornblende.

Diyilizua by GoOgle

48 Gold-Quartz Veih8 0¥ Nevada City Ahd Orasb Valley.

The Dioritb-Oabbro.Pbridotitb Group.

Thu rocks ul' tahiti series, euibracitig UuiriU:, gubbru, borubleiule lOCk, pyrozenite, peridotite, and mrpentiiie, form a series m intfinately oon-ii

'( (l tiiuisitioiis that tlu'ie can 1m no doubt of its close jt-iu'tic relatiouBliip; nor is it possible to strictly Heitarute the rovkn iu the deMxiption.

Under diorHe are here Included the ooarse-griiualiu-, abyssal rocks with nurtnal {jriinitic structure, cUitfflyof Mdtpars

of medium iicidity and hornldcude; biotite or Tiiay sonictiiueM replace the hornblende. The grauodioriteH, au iiiteruiediate group ranging from qnartsHliorite to qnartx-monzonite (Briigger), have already been separated. With the 'ranodiorite h;is been indiidcd several smaller uiasaes and diketi, which juobably are only local prodncts of differentiation of the gninodiorite magma. The diorites have a siliea percentage varying between 51 per cent and ri8 per cent. The lime IH considerably in excess of the sum of the alkalis, the reverse Iwiug true of the grunudiorites. A considerable ot ferromagneslan eilicates is nanalty present.

The tjtihhros, as liere delini'd, inebitlc siTnibii' rocks with liasic feldspars (labradorite or anortbitej; tlie ferrouiagueHian silicates uiuy be either pyroxene, hornblende, or miea.

The pifroxeniles are coar.se-granular, very basic rocks of jjranilie Ktnu ture composed cbieUy of pyroxene, with very small amounts of feldspar.

Tb peridotitea are ainilar roeka oomimeed of olivine and a pymzeue

or an aniphibole.

The KerpeHtitUH are secondary consisting chietiy of serpentine, with minor qmwtitiea of reaidnary minerals or newly formed actinoiite. They are evidently derived from gabbros. ])yroxenites, and pcridotites, ohietiy from thh latter two. It will be shown later that they may also be derived tiom certain ))orphyrites. The aotioii producing the aerpentines is not weatherings but must be regarded as similar to the actiftns efTectin metamoi pliic alterations.

iCel'ernug to llie Smartsville folio, it will be seen that a double wedgeshaped area, determined as gabbro-diorite with masses of pyroxenite) peridotite, and sei pentine, extends from Rirchville to a jxiint east of Grass Valley, itdjoiniug the grunodiorite and diabase on the east and the diabase and sedimentary mcks on the wet. The name gaJbbmdwrite was adopted as a convenient include dilferent rocks bi'lon;fing to the diorite and the ;;abbro families. It wonUl no doubt have been better to designate this mixture of rocks gabbro and diorite. The area is one oC great eoroplexity, with gradual transitions

between the gabbros. diorites, and loxenites, while the sci entities are more sharply defined. iu the northern part of the large urea great

Diyiiizea by

'tmvmnr.) DIORITB-OABBRO-PBBrDOTlTB OSOUP. 49

complexity is added by the fact that the whole has been subjected to more or len inteue dynamometamorpluMB. Seveml pvtK of tbi* tnm IMl within tbe apaoe of the detailed sheets.

THX OBO Fino DIOBITB-PTBOXBiriTB ABBA.

BefSarenoe hiw already been made to this area in the nortfavert part of ITevada OHy tract while diBoaaBing its lodistlnAt oontaot with

the

The Huutheru purt of the area, runiiiug out iu the of a wedge, contains idiiefly dioritea of dark oirior and average granular textme, wi'iithorit);;: Ics! easily than the granodiorite finding rougher ontcropa aud a scout, deep-red soiL

Under the mierooGope the rooks are shown to be diorites with very little biotite and a little quartz, the often included in the hornblende. There is very little pyrite in the rock. Near the Kirkham mine the diorite contains many small iiegmatite veins.

At the northwestern end of the big apUte dike the rock lias changed to 11 clark iricpii, coarse fjramilar pyroxpiiito. roiisistinjf chietly of large irregular grains of a partly uralitized pyroxeue (diallaget), with some grains of apparently primary gteenish brown hornblende with aagite kernels. lietween the pyroxene grains lie small grains of a feldspar, largely converted into micaceous aggregates.

Stuall dikes of aplitic rocks are found in the pyroxenite. In other places close by (800 feet northwest of Coan's mine) there is a larger nmount of anorthite with broad twin Iaiiii'lliL> and propriatoeztinotious; cuusequeutly the rock is here a gabbro.

Still Ikrther north, feet north of Ooan's mine, the coane-grained| dark ro<-k consists of partly uralitizcd aiipito. jrrrciiisli ])rown hornblende, biotite, and tridinic feldspar, with a little quartz and probably also some orthoelase. There is also magnetite (ilmenitet) and mneh apatite.

Still farther northwest, at the Oro Fino mine, dark, coarse-granular rooks appear which are intermediate between diorite aud gabbro. The specimen, from the damp of the mine, is somewhat deoomposed and affected by invssiiic. many of the feldspar lamella-being curved and bent. It consists of au apparently not very basic plagioclase, augite, and biotite; iwobably also some orthoelase and qnartz.

I IU: I'l.K.VSANT FLAT DIOKITK AIJKA.

Jhtoriptitm o/ rook. — Tbis area, e&touring on both sides of Deer Oieek, at the western limit of tiie special map is predominantly composed of a fairly normal diorite of rnai texture and durk-green color, containinj,' a larjie amount of luiniblciHlo. Seen in thin section, the hornblende is brownish -green, partly partly roughly prismatic; the lUdspar Is lath-shaped or anhedial with twin lamellie, the eztino*

Diyilizua by GoOgle

60 ooLtMitrAims twins op cmr Am orass vallist.

tiuuH ut wliivli indicate a biuiivity. A little quartz ia wiiiietiiuea Ibnnd between the grains. Tbe aeridtie alteration has proceeded fSur,

as a rule; iiiiu-h of tlu' horiibk'iide is also converted to uralito, chlorite, and epidotc. On the whole, there is much more of these ftecondary minerals than in the granodiorite. Grains of pyrito are scarce and usually asaociated with epidote; in some cases they might possibly be primary. A partial anatyaia of a typical Bpeciiueu, by Dr. Peter Fureman, gave:

Of tbe CaO, at least '2 per cent, probably 3 cent, must be contained in the hornblende. (Oompare oaenlation of Giass Valley granodiorite.) There would thus be not more than 30 per cent An and 27 per oent Ab, which shows that the feldspars are only of .mednim basicity.

Facie* of the rock. — In many places the rock ts subject to changes in grain and oompoaitiou, some parts of it being rieher Id hornblende, while in some parts the feldspar acquires more proniitienco and some quartz begins to appear. At Carls tunnel, near tlie audit4j contact, tbe rock on the dump exhibits a very coarse pegmatttic structure, and con* sistsof uralitc ( rystals several inches long in a white, itarfly sanssnritic mass, with sp. gr. I'.'JS. To the northward, beyond tbe social maps, the rock gradually changes to a typical lightHSokwed gabbro, and even in tbte area there is undoubtedly a certain lelationaliip with the gabbro occasionally exhibited.

Weatiicriuy. — Deep, rich, residual soil produced by weathering occurs flontb of Deer Greek, and eapeciaUy near the andesite contact. On the north side the soil is kas deep, but the rock is disintegrated and crumbling.

IMaHoH to anrrounibtff nMtt — Toward tbe north and east the diorite

is ill contact with serpen tioe and peridotite, with a rather sharply delined contact. Tontr'K's of serpentine extend into the diorite, as shown on the map. Tbe area contuiu.s an extensive system of dikes of urallte-diabase, which will be described Uiter.

Dcucription. — This is really tbe continuation of the above-described area, emerging from below the sonthem edge of the covering andesitic

tuff. The character of the rock is alsi entirely similar. a <'oarse. dark diorite. There is m some places also the same and rapid change of grain and basicity. The rode deeply decomposed on tbe hill northwest of the Fair-gnmnds.

j 51.24

The Pair-Gbound Abba Op Diobitb.

Diyilizua by GoOgle

Dioritk-Gabdro-Pebidotite Oboup.

Relation to othrr rnckn. — Towunl tliP luirtlH'aHt tlu <'oiitJU't with the dark-green porphyriteji is in phieeHvcryiiulefiiiitc uiid not well exposed, much apparently brecciated uiateriul along it. The coarse diorite oontaius fragments of darker greenstones of finer grain. Along

the north side of tht* track thiw is a considerahh amount of tbis luized luuterial. The contact witii tiic serpentine is fairly tiharp.

MORirr, AUKAS IN Till' SKUPKNTINK.

Smaller uiaieii of diorite, irregular or leu4 8haiM.*d, occur iu {he serpentine. Tb largest one north of the Idabo mine, is sabstantiftlljr like the Fair groond nren, and contains besides some dilces of a bornUendic

porphyrite.

In the ludiau Flat serpentiDe area irregnlar massen of diorite are frequent and probably represent dioritic variations of the prevailing peridotite pyroxeiiite ninfyiiu. In tlie extension of the Idaho ser])entine area northwest Lwyund the special sheets, oa the Newtown road, sinuUer masses of dark-green, ooarse-grannlar homhtenderoek is found, evidently corresponding to the pyroxenites, and consisting almost exclusively of primary, deep browuish-greeti hornblende with strong pleochroiam. No larger areas of this hornblende rock are found. It should not be confoanded with the ampliibolites, which, as here include only tbe dynamo-metamorpiuo rocks iu which tbe hornblende is secondary.

The Hobbhou8B Diobttb Dike.

This dike like iMMly is contained in and gabbro half a mile westof the .Maryland mine. It is a medium-grained, grayish-green rock, containing, besides feldspar and hornblende, mnch pyrrhotite in small grains. Under tlie niieroscoie the rock consists of the usual dioritic borablrade iu irregular grains, lath-like or irregular feldspar with narrow striations, with smaller residnal masaes of orthoelase and quartz and a little magnetite. The strnctme is typically hypidiouior]>hic. Tliere is much cldorite with tin' hornblende, and micaceous pnKlncts with the feldspar. The pynhotite is generally of secondary origin, oocnrring ebiefly with the chlorite.

OABSBO AftBAB.

Oetteralfmham.— Typical gabbros do not form eztenaiTe areas in this

vicinity; most tf the areas occurring as elongated masses in the tiue probably represent, as does the diorite iu similar oocorrence, iacies of tbe prevailing pyroxeiiic orperidotic mother rock of tbe serpentine.

Oaibbro (like behv the Providence mine. — In the dike like masses on both sides of tlie below the Providence mine the is very coarw grainel, consisting of urahtic pyro.veue of light gi'een color and irbitiiib feMspnr, very often with a tinge of brown. The grains average ."i mm. In wentherin, tlie large assume a whitish color. .Microscopically, the feldspars show large aiihedral grains with brood striation, the striations indicating a oompositioD

52 Oolu-Quartz Vk1N8 Of Nevada City And Orak8 Vallky.

between iiml unortliito. Tho is almost wlmlly cotivertetl iuto uralite, fibers of which are uIho I'ouud in the The latter are in part olondfld by mieaeeooa piodneta. Soma ilmenita is niso ]in's(>nt, an well aa flome finely diatribnted pyrite, the latter probably tieuoudary.

(?oMro In the gabbro in the Maryhiiitl seriMjiitiue, one of which ih indiciited on the ma]). TIk' irx k is only in part typical, some of it l'iii<,' scliistoso and dyuuuio I p toward Jouch Bur, in tinlumtinuatioii of the diorite-gabbro seriee of the speeUU sheets, there are large areas of pibbro similar tin- <nii- In rc dcHcribed and also 'haracterized by the whitish i-olor uf the uutvrops; it is here frequently dynamo-metamorphosed, prodnciug lilit-colored actinolite sehista, often also with macb /oisite.

The Min ifUni'J ntthhru. — The Maryland jrabbro area is th' hir pest one found on the area uf the spet-ial sheets, extending lioni South Wolf Creek up to the Maryland mine. The rook is in the main similar to the nno just (h'scribed : it is coarse jrraim-tl, of a prevailiiifi color, and is composetl of nralite-dialluge and a basic plagiocia8.

The exposures are very the deep disintegmtton of the rock rendering it difticnlt to dfritliflu' n-lations with the snrroauding rock. It borders, with a fairly distinct (ont4M't, on the smaller masses and seams of the latter rock oecurriug iu the gabbro. Toward the east the oontaet with the coarser diabaaea of the Maryland area ia very obscure; abundant dikes of diabase, oxtendinir from the main areti, appear to be contained in the gabbro, but iu the ai-a laid down aa diabase there is also, as at Sooth Idaho, more or less |rabbro traversed by dikes of the larker The best s are along the railroad near tlie sniphuret works, but they are very unsatisfactory : the rabbro disiut'grates easily t4> a crumbling mass, while the hard diabase dilics remain tutact, their fragments covering the ground.

Thr Kant Mnriilinnf iitihhro.— Tlalf a mile east of the Maryland mine another gabbro area begins. This is practically included in ser|)cutie, and the rock varies a great deal in composition. While the prevailing rock is the normal, coarse, whitish gabbro, there is also much of darker diabaAic and ainphibolitic rocks, the relation of which to the gabbro is obscure on siceonnt of poor exposures. On the dump of the Chevannes tnniiel much saussnrite or suussuritic gabbro was found.

A little is also found in the slates at flic south end of the small serpentine area uear the Washiugtou mine feet east of the Marylaod mine).

JSfiTteat.— Beginning under the andesite northweat of Town TUk, this

area cxteiuls beyond the limits of the map to a point some distance northwest of the Yellow Diamond mine.

THB mBIAir PI.AT BBBPBimilX ABBA.

Dencriptioii of rorkii. — Tln> SL-rpentine in this is only partly a ])ure rock aud unaully hmrs clear evideuce of its derivatiuu Iroui pyroxenites and peridotitM, in part probably also from gabbro. The reaidtial masses of gabbro and diorite occarritig in it liave already been lu its northwestern jioint uiialteretl pyroxenites appear, while good peridotiteji are exjiosed where the >'ewtowu roai croii8et its western

Wknetherotssomeofthe pnreliglit-graen serpentine with gUstenin}? faces of tlir fran'ients, the jjrevailintr rock is a black to darkbrowu or durk green dense rock, rather soft aud with dull surface, in places Rhowing, however, a peeallar satiny luster. Occasionally, as, for instance, in the nnk from the old tunnel 2,300 feet south of the Wyoming mill (in; N. C), the seriientiue of the appearance just referred to is fairly pure aud shows a grate structure by development of more sharply fibers crossing each other at varying angles. There are furtlier, some tremolitc or actinolitc, a little talc, and abtindaiit irre;,'u- larly distributed magnetite, aud, lastly, clouded anil corroded remains of a pyroxene mineral.

A specimen from the north side of Deer Creek, 2,000 feet west southwest uf the Pntvidenee mine (131 X. C), is a black, apparently linegrained rock with a satiny Inster. The microscope Aawt it to be a vevy imperfect serpentine. There is a large iinautity of clouded residual pyroxene, ]>rob!ib!y enstatitc, traversal in all directions by radiating or crossing fibers <)t serpentine with gray colors of interference. The olivine is not so easOy reoogniied, bat is probably also present. Some secondary actitudite in radiating fibers traverses the pyroxene; a;:;.negates of talc are also noted. Tlie magnetite is abundant, auhedrul or in shan* crystals, and arranged to fbrm an fnidpient net struictnre, best seen in reflected light. Pyrite also ooonrs in this rock, in anlMdial

grains <dosely associated with inasrnetite.

A seriteutiuoid rock of similar appearance from near the contact north of Pleasant Flat shows rmnidns of pyroxene and olivine; the iiic 1i:ivcrsi-s the riiirinal tiiiiierals in net like vi ins comiwsed of a very cryittocrystalliue, clear mass. Talc and actiuolite ai-e present, as usual. It should be noted, however, that it is impossible to distinguish fine micaceous aggregates Aroni talc, and if feldspar was present in the ori'itml rock white mioas might be expected in the resulting siriH-ntine.

ifTealAerinif, — This impure serpentine derived from pyroxenite and

p<'ridotite is m l y resistant to surface decomposition. U forms reddishbrown, rough out-crops, with practically no residual soil. West of Indian Flat a probably thermal alteration has produced a lai mass

of brown or white, cellular, ehalcedtmic rock, loss agates, so called, consisting of translucent clialcedoiiite with black dendritic inclusimiSy have been obtained from this liK-ality.

Diyilizua by GoOgle

54 Uold-Quabtz V£Ins Of Nkvada Citv And Grass Valley.

Pilrttinn to rorln. — Tlio contact with the nmphibolites on tbo L'ast 18 distinct, tboiiKh iusufUcient exixiures do not permit a satiitfiwtoiy eBtablishment of the relation between the Toeka. The eootaet on the west with the wedge-like prqjeoting serpentine maiw has alrend}' been referred to.

THB TOWN TALK BBBPKMTmE ABBA.

ThiH gmall area. 1,.KH> feet Ion;,' and only a few hundred fi-i't wide, is ill i liiir-.K'ter <if riM-k .siiiiiliir to tlir 1ar<;er UiaBS junt dcM'rilu'd. Uesiduul pyroxene, aud ineoaiouully olivine, is contained in the serpentine, as weU as aeoondary actinollte. One apecinien with dense, dark-green, flinty appearance is a mixture of serpentine, chlorite, and uctinolite. On account of unsatisfai-tory ontcrop, uotbiug definite can be said about its rebiUon to surronnding rocks; it lies as a dike-like mass btweeu dark-gteea porpbyrites on the west and black clay-slates on the eiuit.

A similar small area witli some gabbro at its southern end is found north of the Washington mine, southeast of the Town Talk area.

THE MABYLANP KKRPKWTrin! AKEA.

ff/ewf.— Beginning as a nari-ow wedge in gabbro northeast of Newtown and flanked by smaller masses of peridotite and pyioxenite, this

larjie serpentine area enters the special sheets west of the Fair-groondi and between the Maryland mine and (Jrass Valley sends out a long masH southward toward the sulpliuret works. Continuing sontheast, the area mns ont to points again; near the Bmnswiek mine two branches :ire by a mass of rabbro.

Deacription. — The rock iti a normal serpentine of dull dark-green, dark-brown, or black color, sometimes containing veins of ehrynotile; a li{;bt-green crumbed serpentine, breaking in smootli, glistening fragments, is also found in places. Masses of diorite and gabbro ate not abundant in it.

The rock in Hiis area is mnch more normal than is the Indiaa Flat

serjM'ntine. In most of the examined the serpent ionization is complete, no remains of the original minerals being found. The structure is, as a rale, an imperlteet grate structure, by the deveknnent of stronger bi refra< tlbers crossing one at varying angles; between the libers lies less strongly bi-refniotiug serpentine with nndulous extinction. A little talc and actinolite occurs, but far less than in the Indian Flat area. There is abundant magnet i t e, somet imes arranged so as to form a net structure; a dark brown, transhu ent chromite is also noted iu some specimens. Finely disseuiinuted pyrite was Ibnnd in the serpentine 1,700 ftet west of the Eureka shaft embedded in fresh serpentine and in chrysotile veins; it is closely associated with

Diyilizua by GoOgle

tho maffiietito and somotimea iiicliuled in it; in one ]il;u c a cluster of siuall yellow ueeUles was noted, possibly luillerite or sul|)hiUc of uickel* The proMDce of aoine ealeite iu the rook renders it pofldble however, that Home of thepyrlte luay luu to the vein Boliitioua.

North of the arOiiH of the sIhhMs reniuius of pgrroxeiM and olivine ure more frecjuentiy found in the Herpeiitiue.

rock veatherH vwy mnoh like that of the Indian Flat area, in rouj,'h, outcrops; the rocky hills are almost ban-of any residual soil, and are characterized by a scrubby growth of dig|,r-pine and tlioniy (Oeaaotlraa).

Relation to aurroundii r€kB. — The contacts of the .serpentine with tlu' sediinentiry nicks, well as with diabase and anl with the gabbro and diorite, are fairly sharp; least so, probably, tho gabbfo eontacta, bnt the deoompoaitlon of the roeka renders it dUBcnlt to obfaiii distinct evitlciicc as to The rehitions at the St. John shaft are shown m the diagram accompanying the description of that nine. Small bodies of serpentine are ooeasionally fond in the diabnp, as at the reservoir 1,000 fct t smitliea-st of the maryland minOi Xnmerous dikenof diabase and porphyrite are found iu this secpentilie area, and will be discussed later.

TJIK riiOWN I'olNI' SEKI'I'.NTINK AKKAS.

At the Crown Point mine aud northwest of it there occurs iu the sedimentary rocks dike-like masaes of serpentine in close conneotioa with certain bii-slc porpbyrites, to be described later. The relation of the serpentine and )>or]>hyrife is very similar to tli;it in the St. John section, aud the inference is scarcely to be avoided that tho latter rock is subject to a serpentiulsation. Spedmens flrom the New Eureka prospect shaft ami from near the ("rown Point the ence of much actiuolite and some chlorite iu the serpentine. There is also some ehromite. The rock from the latter locality (bridge by Crown Point mill, 116 V.) is not exactly like a normal serpentine, being dark jreen, hard, and showing somewhat spliuteiy flraotore. iiesidual pyroxene wan noted in this rock.

Diyilizua by GoOgle

Chaptkr Iv.

THB lOlCBOUS BOCKS OF TU£ B£D-BOCK SUBIES— (COXTD). THB DIABA8B AND PORPHYRITB OROUP. IMBFIimiONS AND OmXEMAl. FBATUBBB.

Under diabaM are here indnded hypidiomorphio granular rocks oompofled chiefly of a soda-lime feldsimr with augite ; liunibleiule may ly or even wholly replace the augite. The texture ranges from coarse to rather Hue grained, the latter forming transitions to the jKirphyrite group. The Qrpical strootare distlDguishlng it from the gabbros is pramiliir*' or "ophiti*'," liaracterized by long, lath-shaped feldspars, the interstices being Ullcd by the augite. Through a mote granular developiDMit of the feldapars transitions to diorttte structure are eflectcKl. It was proposed to restrict the term "diabase" to thoae rocks carrying basic feldspars (labraIi trite to anorthitc), bat this has not proved feasible without treating too artificial distinctions.

Under diabase-porphyrite are indnded the flner-grained forms of diahaso in \\h'u-h an* contained plicnocntTSts, usuaUy of Iddspar, thos giving the rock a Ktrphyritic habit.

Under angite-porphyrite and homblende-pMphyrite are here indnded the jtre Tertiary porpliyritic rocks, consisting cluelljof soda-lime fddspar and augite, hornblende, or biotite. The structure is porphyritio by pheuocrystt) of any of these constituents. The gronndmass is chiefly feldspathic, ranging from oryptocrystalline to microcrystiUline; very common is a pilotaxitic strncfnrc a transition to the <li:il);isoporphyritcs. in these the feldspar is, as a rule, somewhat less basie than fn the dlabaeea. No glass has been detected, but remains of it might -well liavc lion devitriflcil and thus e9ca])ed attention. The porphyritos are probably chiefly eiiusive rockSi but may also oeonr as intrusive bodies.

Bocks belonging to this grou|> have a wiilc distribution in tIteanM eOTered the special I hey are in general dark-green, rather basic rocks of medium to line granular or holocrystallino derdopment, angite prevailing among the ftrromagnesian sUleates tliotifli lionihleiule also occurs. Collectively they wonM foi iticrly have been referred to as '''greenstones." Th range lu composition from normal diabases, with fhm 47 to 53 per oent SiO* and rich in lime, to quartz-porphyrites of a composition similar to that, of many granodiorites; the latter division is in general se};regatel from the rest ami separately indicated. From the nornuil diana-ses there are gradations into iKnnblendeabases and into rooks with mora

Diabasb Ahd Forphtbrb Obocp.

eu-granitic strnotaie. Afrain, the dittbaae may readily become porphyritic. tht rcsiiltiiip IxMiip referred (o as A more prououucd jrarpbyritiu tstructuru with liiier-gruiued htdocrystalline gnmndman gndnally iMda over Into theiporpbyrltee, lefiBrfed to ftS engine-porpbyrites or Benides thvsv main diyisionfl there are others less prominently represented, aacb as tuurcbites (J. F. WiHiems), or jiorpbyritio folks oonststing ebiefly of pyroxene, and auite-syenite, the latter probably only a fades of the diatwae. There are fUrther great maetee of old tuffs and contact breociaa among this group.

In fiice of anoli a Tarlety of rooks, gradnally changing in compoaition

and striicfiirf and still by iicccs-iit y to )if ri'u'ardcd as a "colojical unit, the limUatiuus of petrugruphical ciaHsiiiicatiou become painfully apparent. It can not Tie regarded as proved that the dilferent area oocnpied by this Heries are of exactly the sume age, but tbe probability appears great that tlx' time of crnptioii of all tlH-s falls witlitii nindcrate limits. Thuy iue much later than tlie Calaveras formation, partly cottteBuporaaeous with, partly slightly later fban, (Jm Maripoea

beds. Granodiorite apfwars to ho the oidy prindpal lOCk vbldl Is decidedly later than the diabaste-xiorphyrite seciea. The flwqnent (wrphyritio character, and eepeeially the abundant

presence of fragmental characterize the grou]>, in contrast to the granodiorite and the diorito gabbro group, as surfate erujjtions, while the trausitiou in granular diabases, on the other hand, tend.s to connect it with the intrusive rocks. It is ]>robabIe that the group represents wliat is lift of the extensive vtdcanoes wliich at the close of the.Iurnssie perioil were built up along the foothills of the Sierra ><evada. The erosion having removed the vpper part, the rwnaining cores are exposed. The progressive eruptions <if n'w material an the volcanic masses piled up will to some extent expbiin tiie closeJuxtjiiKtsition of of intrusive and effusive types. Professor Iddings's descriptions of the Electric Peak ranks offer many analogies to the jihenomena here pre> sented. It may not be ainiss Ut call attention to the fact that the rtn-ks most resembUng the cH'usivu types of modern andcsites are found Banner HID, in the highest parts of the area, bnt no distinct law governing the distribution of tlic diflerent structures can be formulated. ' Finally, this group has been extensively subjected to metamorphism, developing uralite, epidote, chlorite, pyriie, and cer minerals, and sometimes converting the rock into amphiboUtio schists.

A majority of these jMirphyrifes are, atriefly sjeakin;r. the somewhat altered and perhaps devitrified equiviUent.s of the modern andesites, and might be called "apo andesites," according to a recently

suggested iiomenclatute.

This or a similar clussitication has not been adoptiil because it was believed that great conltisinn would result. Tlu*. gap existing between the Tertiary andesites and the Mesosoio porpbyrites is, intheBierra Nevada, very wide and marked.

58 OOLD-(iUAKTZ VKINS ()F NKVADA CITV AND GRASS VALLEY.

THE DIXSa IM THE FBDEBAL LOAN ABaiLLlTBS.

Qi ni riii fvdtuttit. — Very many dikes are eoiitainwl in the ontact-uietuiuorphosed rock of this ara, but luust uf tkeui are of small extent and irn>(,'ular fonn and ean be traced ouly for short difttaneei. ItlH rarely possible to trace them with great accura-y under flie deep coverinjLf of residual soil; the of ;ireat <'x)'iit >,Mineil by the abuiidaut fraiunts is corrected by inKpccliuu uf fresh exposurcH, along the canyon of Deer Greek. Although occnriiDg abnndantty cloee up to the jrranodiorite, none have been found in that rock. They usually contain a considerable quantity of sulphides, as do the argillites in which they are contained, and irieo, as the argilliteis aecondaiy biotite.

Fourchite. — Tlie lounrhites, according to J. F. Williams,' are characterized us porphyritie rocks with pheuocrysts of uugitu in a prevailingly aagitic groaDdiDMS. Books of this character, really the porphyritio e(|nivalent of jn Toxenite, oecnr in this area at two — as a small dike a few feet wide at the lout bridge iMO feet northwest of the Federal Loan mine (S2 N. C), and as a larger dike at the andesite dike north of Willow Valley Creek. The latter is adjoined simthward by another dike of quartz-porphyritic character. The dark-green rocks carry augito crystals, colorless in thin section, green in specimen, several millimeters large, of stoat prismatic habit, partly uralitized and sliowin}; peculiar twinning, sonietinies with polysynthctic lamella-, probably parallel to a dome or a pyramid. The grouuduias.s is chietly u tine aggregate of small prismatic or aahedral nralite grains with a little gericitized feldspar.

Diorite. — A dike-like mass of dioritic rock occurs on the divide between Scotts Flat and Willow Yalhy, at the road to the Ibraer plaoei It is a dark-green, medium-grained rock, eousistiug of roughly idiomorphie, brown, partly blea< hfd liornblende, lath shaped jilagioclaso and a little orthoclase, the latter ceuieuUug the idagioclase prisms; very abundant titanite and pyrrhotite, the latter pomlbiy primary in part; niiK'li clilnrile cpidnte. Though a diorite, tilO rock is tO to b<- closely related, geologioilly, to the diabase ern))tions.

I'vrphyriu. — Dikes of this character are most frequen , and the rocks may be classed either as liomblende-poriihyrites or qnartz-honibleude- They are in geneml dense, dark-gray rocks, with a tinge of green or brown, with pheuocrysts of hornblende, in some cases up to S em., but usually 1 to 3 mm., in length. The ftldapar phenorayets are less eonspicnons. T'ndcr the microscope the hombh'iide, Avhile more or lets aralitic, bears evidence of having been originally of dark-brown color; maximum extinction, 20. The feldspar pheuocrysts are well defined, but usually obscured by serii itic and epidotic aggregates. The hohn rystalline groundniass is, in tlie (piartzose of a tinegrained, allotriomorphic character, while in the quartz-free roi ks it

Diyilizua by GoOgle

Diabase And Pokphykitb Group.

readily assiiinea a |i]<itaxitic stnictnro by tlio microlitir dovolopment of the lelUiipars. The grouiulina8 is prevailingly cuinposed of feldspar, tboDgh in (he qnnrtz-free porpbyritM thre are also small prisms of nralitie hornblende. Many nf tlie roekn contain findy disseminated, reddish-brown biotite in the groundmass and in tlio nralite crystals; this biotite is probably not primary, but has been developed by metamorphic ])rooesaes. It can soaraely be dne to ooutaot metamorphistn, for tlic granitic contact is for many of the occiiiTcuceK sevonil tliousand feet distant. A similar development of brown mica will be shown in tiie metamorphosed diabases of the Nevada Oity area. Mafpietite is abundant, as is pyrito, and esjiecially pyrrhotitc. In part these snlphides are doubtless secondary, but iu other sections (3'2 N. 0.), where Intimately intergrown pyrite and magnetite fills many of the hornblende crystals, a primary origin suggests itself stningly. Chlorite, eindotc. and scricite are abundant. On the wliulc. the nwks may be characterized as greatly altered, though uo mechanical collects of dynamometamorphism are visible. Specimen 23 N.G., from near the edge of the Banner Tlill area, 200 feet soutli of the Scotts Flat road, was analyzed. It is a dark-gray, fairly fresh rock, porphyritic by black hornblende crystals of prismatio habit, aboat 3 mm. long; the feldspar phenocrysts are small and not prominent. The groundmaM is den.se, grajishbrown, with splintery fr.icture. Tiider the microscope the hornblende is greenish-brown, and shows sharp idiomorphic outlines. The feld- 9pm are filled by epidote and a serieitio mineral. The gronndmass is a very f5iie 'rained, allotriomoriihic, feldspar-quartz np-ogatef with ft great development of small biotite foils. The fidlowing aiwIyaiB of this coclc was made bjr Dr. H. H. Stokes:

TiO, ,

PtO,

So, ,

Auo,

FsO

CbO ,

K,0

NiO .'.

H,0 below 110" C H4O abore IVP C

Diyilizua by GoOgle

60 G0L1&gt;-Quartz Veins Of Nevada Cit¥ And 0Sa8S Valley.

The clKMnic:)! of tliis rock approaches very t'losely that of soiiio grauodioriles. Making due allowance for the CaO contained in the bornblende, there is evidently moie Ab then An, and, beaidee, not ao little orthodaae.

TBB BAWMBB BILL DIABAtn AMD POBPBTBITB ABBA.

2f0Rt— Aa shown hj the general map (PI. I), this area is enttrdy

snrroandod by sedimentary rocks of the Calaveras formation. The part of it sliown in the sontheast corner of the Hanner Hill sheet is of almost bewildering complexity. Were the exposures better it might be possible to further aabdivide the area. It is, however, nnqnestioniibly a geological unit, and iwcording to the available the rock types are closely connected by transitions. The occurrence of brown hornblende eharaeterizee most of the rocks in this area.

jyencriptinn of rockM. — As no general description can be given, it is necessary to single ont principal types. No. 71 N. C. (Banner Hill bears N. 20° W., and is 4,700 feet distant) shows in a grayish green groandniass white feldspar crystals np to 1 mm. long, and stout, matic, black humblende to 10 mm. in length. I'lidor the the idiomorphic brown hornblende, with extinctions about 20, shows peenliaily rounded or oomded OBlUnes; some stout, partly nralitised augit4 (uystiils are also proseiit. The idiomorphic feldspars are largely converted to epidote and niiciw;eous minerals. Grains of ilmenite or titaniferons iron ore partly converted to titanite are rather abundant. The gronndniHss is apparently holocrystalliue and consists chiefly of Rmull iiiicrolites mixed with small grains of uralito and ohhwitay The rock is a typical

A spedmen from the lower Qoaker Hill road near the edge of the map (57 N. C) is dark ;;ray in color with a tinge, and indistinctly by small feldspar and augite It contains abundant pyrrhottte. In thin aeotion the colorless, prettily idiomorphic aogites arc partly ftldspars being oompletdy deem- jMJsed to ejiidote, micaceous aggregates, and cloudy mas.'cs, probably kaolinite. The grouudmass is hulucrystalliue and consists of mediumsiced feldspar mierolites, with nralite grains, chlorite, and a llttie dirty* brown biotitc; there is very little magnetite, but pyrrhotite is extremely abundant and apparently of secondary origin. In structure this rook Btands between diabase porphyrite and an augite ])orphyrite.

The rock firom the extreme southeast corner of the Banner Mill area is a very decomposed, fine grnincil, hut otherwise iiormal diabase.

A specimen taken at a place where lianuer ilill bears N. 'M' VV'.and is 4,fiOD ftet distant, is a dark-green, coiwae, granalar rock efnnpoaed of large (up to mm. in diameter) augite crystals atuT 'rains. light green in color and surrounded by a rim of black hornblende. Between the angites lies finer-grained white feldspar. The micttoscope shows large grainaaod impeTlbcterystals,<>fteB-twinned,of

Diyiiizea by

Diabase And Porphtrite Group.

asuully by tt border richer in iuclusiuuH, uhitslly siuull Iragmente of brown homUendo; tltis aicaiii Is stuTonndccI by an outer rim

of I'loar brown humblondo, touring every evidiMu-f of \mnn a primary constituent. TIhmo are piaiiis of ni:v>,ni<-tito oiilrticnitc in tlio hornblende and alsu uiu(;li leucuxeue. ryrite uccurH occusiuuully, with chlorite or intiergrown with magnetite. The plniochwe is related to labradorite and (xicnrs in Hiiiiiller, sharply hith shajiod crystals iK'twccn the large augiteM; it is frequently included in tbe hornblende, uiure rarely in the augite. Between the laths lies brown hornblende, more rarely aagite, (K casionally iptartz. A little chlorite, epidote, unilite ooenr iu tbe rock. The stmoture of the roolc is distinctly diabiUiic.

Still another rock, oocnrring on the Quaker Hill road near the eastern limit of the spi'<ial sheet, is a niodinni-rained hornblende diabase. Both the brown horubleudo and the feldspars are partly idiomorpbic, though Bometimee the latter determines the outlines of the former. This rock is extremely rich iu probably 8e'ondary pyrrhotite.

Compoitition. — No analyses of these rocks have been niaile. On the whole tlie (;>ui{>08itiou is doubtless that of a diabase, though the porpliyrites may be somewhat more aeid. Qnartsporphjrrifeee do not to o!<rnr liere.

Wfuthering. — The ruck weathers to a deep, reddish-brown soil of clayey character. Tlie disintegration of the rock has, howevor, not

attaiiUMi any tiepth ap])r(>a4!hing that of the raiiodiorites.

h'l ltilion to other rwk. — On the northwest the area borders against tbe argillites of Banner Hill, and the contact is of a complicated character, a zone of contact-breccia hiUf a mile wide separating the two fontiaf ions. There are, in fact, no distinct <"oiitaetH. Tlie massive rocks gradnally change to a porphyrite-breaaa of generally small, brown or greenish, firmly welded, angular Aragments of hornblende-and angite- IMirpbyrites, with from cryijtocrystalline to pilotaxitic proundmass; the feldspars are usually exceedingly altered and uralitiv aggregates are common. Besides, the breccia contains move or less nnmerona sharp, gray to brownish fragments of siliceous orgillite. often of the appearance of hornfels. This breccia cliaracteri/ed Iiy containinpr a very large amount (if pyrrhotite and a little pyrit-, w hile magnetite generally is absent. The pyrrhotite appcMS to be, largely at least, secondary

and dne to metamorpliiiprocesses.

Sortbwosterly over the summit of Banner liill the sedimentary fragments Increase, entirely predominating in the breccia, which thea flnaDy grades into unbroken argillite.

THX PITTSBUnO OLiBASX AKO POBPHTBITB ABBA.

Sstent. — Begi tilling iu the southwest comer of tiie Banner Hfll tract and extending diagonally across the Nevada City tracts is a large area of rocks of dark-green color and diabasio or porpbyritio character.

62 TBIHS OP IfEVADA CITY AND OBAM VALLEY.

Separated by the Muriposa Nlutc.s, a part of it extends north of the

and, iqpcaiing a'uin on the north side of the audeKite liill. colli mimics as a narrow ilikc like mass in the diorite of I'lcasaiit I'l&i, The jiorthwestern part of the luuiu anm is very uiiich altered by metamorphio proceases, which indeed to ome extent have aifeeted the whole mass nmst Vio described separately.

JJmcription, of rovkn. — Guiiig up the iiortheru branch of Wolf Creek, above the Washington mine, one meets with a great variety of coarser diabases and hornblende diabases with iiner-fined liorub1ende-por phyrites. In the southwest eorner of the Ianner Hill frat tlio hornbleiide-porpbyrites jtrevail. A spceiiueu of these, taken at Thomas ranch (80 v. C), carries in a dark gnmndmass ftldapar orystals 1 to 2 mm. loiif,' and lar}:er llaek hornblende needles.

Under the microscope the feldspars appear very much altered into mieaoeons aggregates. The brown idiomorphio hwnblende is partly converted to green uraltte with slightly smaller extinction. The gnmndmass is pilotaxitie, chiefly feldspathio, and shows How structure around the pbeuocrysts. Small foils of brown mica, also a little chlorite and nralite, occur in the groundmass. Fyrite is rather plentiful, often intergrown with niairiKtitc. Roth magnetite and pyrtte CK'Cur as grains in apparently fresh hornblende.

This rock was partly analysed by H. N. Stokes, with the ibllowing result:

Per fvnt.

These figures would indicate a rock with some quarts and a soda*Uine feldspar approaching uudesinc. Along the orest of the ridge and about Herring's reservoir the rooks

are, as a nde, fine to di use, and of dark Mcen In dark browncolor. The microscope shows them to be tufl's of augitoand bomblende-iwrphyritss containing small fragments of these rooks, larger anhedral grains of auMte or feldsjiar, and some iVagmentS of sedimentary rocks. About the IMttsburg mine and from there on northwestward, greatly altered, dark-green, niedium-graiiiCHi diabasic rocks prevail. The angite, nearly always more or less uralitized, is very prominent and occurs as anhedral or ron;,dily idiotnorphic grains which often show a tendency to become ]orphyritic. Where, besides this, the quantity of aagite is great, transitions to the flrarcbites are formed ; such are the rocks in WoimI's Kavine, 1.20() fwt below flie Nevada City mill, and on Gold Flat, 3U0 feet west of East Orleaus ttuiuel. The

CaO. NsiO

Diabase Avd Pospryritb Oboup.

feldsiiar, nearly always greatly decumiMseU, in in part lath-like, iu part more anlMdral, the widespread altenon making it difBenlt to obtain

good oti the whole th(> .structure is only partly normiil diabaaiCyaod dhows approxiiiiiit ion tu the dioritin.

Angite* sud honibleiide iwrpbyrites are aim present in titis area, as, Car instanoe, north of the Fair-ground. Here the jrayisli brown ur greenish jwrphyriteH contain Hnuil! fchlspar crystals and liornbleude iiecdleH 3 mm. lung in a compoHccl chiedyof laths and short prisma of plagioelaae, probably faibradorite. Another rock in the same vicinity is an altcreil aupitc jinrpliyntc with jdienocrysts of plapiodaso and pyroxene in a groaudmass of micropoikilitic strnctura characterized by micralitea and grttins of feldspar in larger quartz grains. This structaro is very anosual.

The best are found at the tnnncl on the sonth side of Deer Creek, 900 feet below the ilome mine, where the contict with the Mariposa slates happens to be laid bare in the bed of the oreek. Fig. 1 ilhutratos the expoanree and aflbrda a key to the wbcdeeomez series.

TtO. 1.— Sm-Uoo at tiinDPl tOO (rrt IivIok- Homo mioK, WHitli Sid* of UMrCmk. gkbbro) k, MrpMf tliir: r. Iilnrk nuulpiMa cUv alto with tuffnocon* MlirtWiit 4. ilrtlW twlf 1 IWHiM—

Titr . /, auniKwhat acbiaUwa.

The black MariiMjsu day-slates begin at the tunnel and adjoin the serpentine on the west; they contain layers of tuffaceous sandstone and are again joined on the east by a dark-brown, fine-grained tnff. This tiifT shows under the niicmscojMi colorless fresh augito fra{:nu*nts. in jiart altering to greenish uralite; between the augitea lie fragments and aggregates of feldspar. The rock is greatly altered by development of secondary amphibole, biotite, etc.

Adjoinin;,' this full' is a flick of normal frcenish jiray liornblendeporphyrile with black hornblende phenocrysia and smaller white feldspars. East of this again is a greenish-brown, distinctly schistose au;;ite porphyritc -greatly altered by secondary minMral jrrowth.

Uu the it probable that the homblendu-porpliyrites are in part later dikes in the tufft and diabases, though th nndoiib& ediy in ;:cncral belong to tlie same period of eruption.

and pyiThotitedo not appear extensively in these rooks in the Nevada City tract

Diyilizua by GoOgle

64 aOLThqVAKTZ YEOrg OF VKWADA CITT AMD GKA8B VALLMf,

TBM rUtASANT I LA I UBALITE DIABASE DIKKS.

Ocvurmice. — Across tlie diurito mass of Ploasaiit Flat extends a narrow area of fine-graiued, rock, very evidently the oontiDuatiofii of tiM pcnpbyiile anm nortii of the Fairfnnd, and similar rocks are fmiiul at many other in tlio rlioiitf mea.

Aooording to tho evideuce obtained at the narrow prumoutory sepa* rating Pleosftnt Flat flrom Stocking Flat, as well aa at Mveral other localities in the vicinity, this rook occnrs as dikes in the diorite. On the hillsides the deep weathering makes the contacts uncertain. Very fine dikes, firom 4 to 6 feet wide, of the same rock are exjiosed at the contact of diorite and serpentine at the head of Stoeking Flat; they

also occur ill the sorpciitinc.

Description of rockt. — All these rucks aiechietly flDe-graincd diabases, greatly altered by nralitization, which as a rale has lelt no angite, and by a more or less extensive recrystallization of the whole mass. A specimen flrom the contact dike, head of Stocking li'lat (1G8 N. C), consists of small grains and imperfect crystals of vrallte In a feldspar mass which on the whole has a diabasic structure, although many of tha laths are and transitions to dioritic structiiro appear. The ciiuractcr of the feldsparH can not well determined under the microscopy as vnry muck secondary biotite and hornblende has developed in them. Ilmenite or tltanifecoas iron ora is present, but not any pyrite.

A partial analysis of rock by Dr. Peter Fireman gave:

Takhig into eonsideratiott the llsct that several per cent of the lime must beloiifT to ths nfalita, it is apparent that the fUdspar iproaehes

an uudesiue.

One these nralite-dlabases contains a few small prisma of brownish, probably primary, hornblende, and In the same area are many smallMr dikes of borablende-porphyrite.

WtBikertng. — Like the Banner Hill diabase and iKtrphyrito, the rocks in this area are deeply decomposed, and weather on the surl'ace to the same dark red clayey soil, from which occasional outcrops of more resistant rocks protrude. This fact makes it extremely difficult, except along the more deeply trenched creeks, to clear u|) the genetic relations of tbe diflTereiit varieties ami their relation to other formations. On the Ked llill, and especially on the slope of Deer Creek lacing north,

8iO.. CsO.

Na,0

DIABABB IHD FQBFSnum OBOUP.

the surface decomposition and oxidation reuciies a depth of 20 feet or more.

Rehition to nthnroHn. — Toward the arjjillites and schists of the Calaveras formation the diabase and porphyrite border with iutrnsive eontaeti In lAe Mmlbhwcateni put of theBaaDcr Hill traet there ate abtitidant cotitact brt'ooias and dikes in t1u> arllites. At the bluflf justeatttuf the Home mine (DeerOreek) the nearly maiahre uralitediabaae cats aeroas the Oalaveraa eontaet-tnetaniorphosed qoartcitie Bohista, showing the later and intrusive charat-ter of the furmor.

From the Home mine northward there are many dikes of diabase in the sedimentary scbista. To eome extent they are pressed and converted into sceondaty aggregates, bat at many placea, as blow the Wyoming; mill and in Bavine below the UTevadaCity Biillt the relation of the two rocks is unmistakable.

The Mariposa olay-data appear, aa indicated bgr tiie relations stated above, to have been laid down practi<-ully contemporHneonsly with tho eruption of the diabases and porpby rites; this is lurtber confirmed by the tnAioMmB ezpoenres in the Herrimao mine and a short diatanoe above the Washiugtou mine, where the tuffs gradually change into clay-slates, a relation ezpresaed on the map by the interlocking obaracter of the contacts.

The relation of the series to the diorites and serpentines has already been referred to.

THB DIABASB DIKES IN THX XABTLAVD SEBPSNTnfB.

To the north of the railroad in the vi(;inity of the Maryland mine the serpentine contains a number of diabase dikes, usually following the same direction as the veins of the Idaho system, that is, wet-north west. The width of these dikes ranges np to 60 or 100 feet The best pre> served rock is found in the hanging wall of the ICeiitncky niin* it is hard, greeuish-gray, ueilium-grained, and contains small grains of pyrite. Under the microscope the more or lesa regular lath-shaped feldspars with narrow striation and extinctions suggesting andesine are prominent, and their arrangement is that of tlie nornuil diabase Structure; they contain abundant chlorite and whit<.t mica. There are reuatna of colorless aogite, bnt the mineral is mostly emiTerted into uralite, epidote, and chlorite, the latter filling the triangular interstices between the feldspars. The titauiferuus iron oieia converted into milky

Other dikes on the City roiwl opposite the Coe shaft and 500 feet northeast of it are similar, the latter containing remains of brown hornblende. The dike-like mass beginning north of the Maryland mine and extending np toward the Sing Hill is extremely afltaeted bgr cblo* ritio decomposition, but was onoe probably a diabaaai

tltanite.

Diyilizua by GoOgle

6$ OOLD-QUABIE Tlim OF VKVADA CRT AHD OBASB YAUXt,

JS!(it.— Beginning on iSoutti Wolf Creek, tbis area extends np to flie roeorvoir aootheast of the Maryland mine in a roagb creecant fbnn.

Dencrrpiion of rock. — The rtx-ks are dark-green, niediamto Ana* grained, normal diabases, characterized by tbe preaenceof hornblende besides the angite.

A typical rock, nnnsnally fresh, occarH on this road 426 fiaet west of the reservoir above the Matyhiml mine (121 G. V.), It iB nodinillgrained and eyries mucli pyrrbotite in small grains.

Under tha mleroaeope the fUdspara iqipear in long lath-like firm, in part alo as im-pilar rriiins. The twin lamelhi' are rather broail, but the symiuetrical estiuutious indicate that tbe prevailing feldsjiar is less haaae titan the labtadwtta. Batwaan the laths lies, in places, a litHa of a Una-grained, interwoven aggregate of feldspar, sometimes sliowing an approximation to sphenilitic struct ure. The anpife is eolnrlesa and shows imperfect outlines, indicating that it8 recrystallizatiou in part preceded that of the feldspar. Most of tha aagites are aommnded by a fringe of evidently primary brown hornblende. There is very little ilmeuiteor titanic iron ore, but a large amount of pyrrhotite and pyrite, the occarrence of which in tha ftaah anita and ftldspar raadeia itspri* mary cbanuter evident (fig. 2). tha intentioaa between tha feldspars are filled by chlorite.

An anulyi8 of this rock by Dr. U. N. Stokei< gave:

Parent.

CuS.. AI..O,

Trat'.

cos

KeS: . . HoO.. CaO... MffO..

K.O...

Traoe.

Diyilizua by GoOgle

Uxdibxx.J

DIABASE AND POUPUYRiTE GROUP.

G7

The rock appears to be a very typical diabase. Considerinjf tbat several Iter cent of the Cat) niuHt belong to the aagite, it is at once apparent that tbe average ronaposition of the feldspars does not reat-b but is rather that of an aiidcsine. Sulphide has in the analysis been calculated hh FeSi, only lhat being in the sample; in the specimen from same outcrop from which the thin sections were taken a large qnnntity of pyrrhotite was identified ly Dr. Stokes.

Other rocks in the vicinity are similar, but usoally contain more chlorite; in some the pyrrhotite is more or less complet'ly repla4-ed by bla<;k iron ores.

The diabasic rocks from the hanging wall of the IdahoMaryhiiid vein are grayishgreen, extremely clilorilic HH-ks, often containing iiiuch carbonates aiul In thin section the all iK'rvadiiigclihu ite generally veils the <rigiual character, but it is suspected that sevend varieties of roi-ks are present. The rock from the hanging wall, tlftceiith level (14,> (i. V.), shows chieriy a mass fehis])ars of im])erfeet lath-like form, between which lies much chlorite. The extinctions indicate a rat her ucid ]ilagioclase. Other slides, from the sixteenth level near the incline, show a chloritic mass in which lie very long and luinow lath-like fehlspars, the structure in fact aitproaching the jiilotaxitic ground niass of some of the rites. Still another specimen, from the mine dum]), shows a distiiH't tnflaceous character. This is not so surprising, for the workings of the mine now extend under the area indicated on the surface as schistose porphyrite. which area in fact is largelj' of pressed porphyrite tnff.

A partial analysis of Xo. 145 G. V., by Dr. II. N. Stokes, gave-

r.7.!U

C'ttO l.Ka

K;0 21

Na.o KOr.

Tlie large )ercentage of Na..() and the small amount CaO are very unexpected, but the rock is much altere4l and it is not safe to <lraw any con-Iusion as to its original coii]])o.sition.

The principal rock exitosetl in the shaft of the South Idaho is a very

68 OOLD-QUARTZ YBINB OF WEYADA. Om AMD QttAM VALLEY.

typical nralttelabam. Between large, long, and Blender latlw of ftldf

spar, well filled with secondary epidote, lies flbrons, pale-green, nraUtkl bonibleude. Narrow veius of a white ininersl cross the specimen, evidently related to epidote, bat showing excepdonally low colors of interference; the extinction is oblique to the well-developed cleavage> A jNurtiil Mialysia by Mr. Qeorge Steiger showed tbe mineral to contain :

aO;

MgO

Icaltkm

Far en t.

aoiio

Vei7 little.

Tbe mineral mast thas be regarded as an epidote exceptionally poor In Iron.

Tlie rocic in the sharp raikoad carve 2,100 feet south of tbe Maryland mine very tine grained aralitic diabase, m which, however, the typical stmctare is less well developed. Remains of augite and brown liorn- Idende were noted. The slide contains veins filled with white epidote and chlorite, together with a seoondaiy mineral with strong doable refraction, probably scapolite.

RdaUm to other rocks.— The irregular contact toward tbe gabbro on the west liaa alre:uly been noted, the diitbase intending as dikes in the former rock. On the nortliej).st the contact toward the terpentine is distinct. On the east the diabase borders, with extremely indistinct contact, more in thenatoreof transition, toward theaobistoseporpbyntebreccia.

THS AirOITB-BTSinTB OF BOUTK WOLF OBBBK.

Half a mile east of the OnisH Valley railroad station is a small area of a grayish-green, mediam-grained rock of diabasic appearance, nsualiy containing scattered grains of pyrrhotite. Tbe rock ocenrring 1,200 feet west of the lower snlphuret works (04 G. V.) consists, as seen in thin section, of plagioclatw crystals much clouded and filled with micaceous products, and angite as short stoat crystals or filling triangular Interatioes between the fehlspar laths. Cementing all these constitnents is a fresher and cU'arer feldspar without twin lamelhe, which evidently is orthoclase. Stnall amounts of uralite and chlorite an present, while most of the titanic iron ures nro converted to lenflOzeoe. A partial analysis of this rock by Dr. II. N. Stokes gave

a. 93

Diyilizua by GoOgle

Diabase Amd Pobphybitb Gboup.

The presence of sik li a large quantity of KtO in this rook is romiu k- able utid nllicH it the aiigite-Ryenitefl, or more correctly to tlte mouzoiiiteii of Brugger. It is uot, however, probable that it is a geoloincally independent body, Itor itn nfflUatkMMi are clearly with the Maryland diabase area, anditia probabl}* only a facies of that rock. The relaUous of this area to the vnrrouudiug serpeutiue and Calaveras fbnnatlon are obsenred by the extensiTe weathering.

TUK AtiU POBPUVKIXii; UIKJ! IN TUE CAL.AVKBAS VOBKA,-

Tion Op Oba88 Vallby.

The medium graiaed to aphanitic, dark-rrn dikes in the GalaTenw formation nearcHt to the granodiorite are, as a rule, fine gniined diabases and diabase-porphyrites, iu!iliti/<'d in part. Tliey frequently contain pyrrhotite intergruwn with black iron ores; at least a part of this pjnrliotite is ptobobly primary. The raposnres are nob sstisflie* tory, the dikes occurring in the t ciiltal part of the city.

From the Crowu Point to north of the New Eureka there extends, in doiMt oonneetion with the serpentine, a series of masses of ▼aiiDg structure. They are cliielly diabasic rocks conalstingof aufite Snrrouiidel by brown hornblende, feldspars witliout pmnounced lath shape and often not striated, pyrrhotite, and bhu;k iron oren. But htnnblende-aagite-porphyrlteswith groond* mass alM All of these rocks arc intensely altered ; the aiigite and hornblende ia changed to uralite, bastite, serpeutiue, and chlorite; the serpentinisation is sometimes very pronounced; the feldspars aie altertHl to stroii((]y bi -refracting aiM-eaten, wliich in part are muscovite, in part probably a scapolite. The black iron ores are <:converted into leuctixene and chlorite, while sometimes secondary pyrrhotite is also found.

In the New Eureka sliaff a series of very peculiar altered scrpentinoid rocks were found, consisting of a line melted uiaHs of chlorite and serpentine containing large distinct foils of white and reddish-brown mica. It seems evident that the <Iiab:Me atul porpliyrite are here undergoing a process of seriMintinization, but in what degree the seriieutine to the northwest has resulted from these rocks is not clear.

In the St. John shatt a very varied and interesting series of rocks have been exposetl. The relations of the serpentine this are indicated in fig. 21, p. 22U. The rocks comprise hornblende-diabases, sometimes also with primary brown miea; granular rocks oonrisling of reddisb* brown nucn, feldspar, and abundant <iuartz: and, finally, rayish-green quartz-borublende-porpbyrites. The latter carry idiomorphic hornblende and feldspar in a hnlocrystalline gronndmass made npof imperfcctly lath-like iilaiodase, between which lies unstriated feldsiiar and quartz. Nearly all of the rocks carry pyrrhotite in infergrowth with magnetite, and the former is in part quite surely The miuorals in the rooka an eztnmely altered to bastite, chloritoy micaceoai

70 Gold-Quartz Of &gt;&#x27;Evada City And Grass Valley.

products, and ]irubably hImo to Hcaixilite, by tlie ordinary inetamorpbio prooeMieH. Theniiul waterH bnve in uddttioii produced abuudaiit cal> ctte and pyrite.

It appearH an if tlie tiiial reKult of tbe metamoqihic proceHses would hmve been a serpentinoid rock consisting of serpentine, cblorite, and aetiDoIite, in ubich lie larger bustitc crystals.

Tii£ North Star And I&#x27;Uupiivuitk Area.

Extent, — This area extends in roughly rectangular form from near tii Xorth Star up toward the northwestern audesite area. It is bounded

FW, 3.— InlcrfiTowlh nf irriinarr pjrrite *od pyrrhoill< with titanic Iron orr; In dUhiwic <34 0. V.(. Mitfitilii-ii 112 dinnirtpn. a. burnbleuili.' , c, ; d, tiUJiic iruu urei r, J. pyrrhoUt*'.

by tbe Calaveras furniation on the west luiil by the ranrxlioritc on the east, north, and south.

htHvriptiun of nivkit. — In the southeastern of I lie area diabases prevail, in part very fresh and unaltered rocks. Typii-al specimens were obtained feet soutlieast of the North Star mine i.'t- (i. V.), .'MHIO feet north of the Omaha mine (it G. v.), and 1,3U0 feet north ol the same mine (lOH G. V.).

umMBBii.] DIABA8B AND PORPHYBITB GROTTP.

The aeoond of these (34 G. V.) is a medium-grained, dark-green, freah rock in wlneh llie black pTroxene and liirht-green feldspars are

plainly visible. Grains of pyrite pyrrUotitc are scattered through the mass. Under the microscope the rock is shown to be almost the only aecomlary mineral beitijo: n little chlorite associated with the lioriiblendCk

The ]ilagioclase occurs partly as Ion;;, latli-like crystals with narrow strtatiou, the extinction indicating an oligoclaMe or andesine, jmrtly also M imgular graina indenting the laths, the effect being often a ragged or pat*hcd appearance. Many of the irregnhir fi ldspnr R-rains do not show twin lauielhe. The augite forius colorless.H graiuii, rarely idimiioirpliie,bnt often notching the feldspar laths, the whole indicating a more or less siniultaneons crystallizatioti. Tlio augite is sniTouiuled liy sharply deHued, brownish-green hornhleutle, not always of the sawe orlentatioii. This hombleode la evidently a later magmatlc giowtii, and not a secondary mineral. There is probably also a little qnartz between the grains. The black titanic iron ore, pyrite, and pyrrhotite are dearly of primary wigan, and the earUeal inrodaetB ct consolidation, being included in all of the other mincnls ftip. The three minerals occur in very intimate intergrowth as irregular grains, the anlphldea being included in the oxide, and vkse Teraa. The titaaie iron ore is most abundant. The stnicture, while in jf-ncral (li;ib;iaic, is not very typically so, on accoout of the less perfect lath-like develop> aent of the feldspar.

Thia rock was analyacd by Dr. H. V. Stokes, with tiie fidlowing resale:

IVreant.

Sa. 19

Naoe.

8.M

of MlflhUM.

8iO*

HnO

BaO

CaO

M0

K O

bdow llOo 0. H0 above 110 C.

a Kr< t Mini Ki'tO| only npjiroxintutr, on ju'4-ciuiil of jir CatoulaUrd mm FeSt. bat much i'Vt**! olo pi*iMiiL

Diyiiizea by Gopgle

72 CKyLD-QVABTB TnM VSTADA. CITT AMD OBABS TALLVT.

The rock is a typical diabase in coiuposition and very similar to the IfiNyland diabue. In all respeotB imilar to tUa rock la the apaoiaiaia

32 Ci. v., referred to above.

Other specimens} such as 1U8 G. V. and 114 O. V., at Central North Star, show a madi more typical dlabaae aeraetare. Th are uraUto* diabiues, with a large amount of bbu k ore.

The rocks in tin-vicinity tht> Xorth Star mine are in preneral finergrained, dark-grc'Mi, uud frequently porphyritic by small feldspar and mcwe nurety aagite crystals. They may in geneml be characfewlaed aa nralitic diabase ii'n''yt*® ranging down into uralite-porpliyrite with pilotaxitic grouudmass. These rocks are greatly decomposed, abundant oilorite, epidote, and roicaoeons prodnot being formed, as irell m lenroxene from the titanic-iron ore. The feldspars are not recrystallized as in the typical dynamo-metaiiiorpliic areas, but alt'r into epidote, micaceous products, and perhaps also Segregations of aeoondary piodueta ooenr, chiefly cbaracterued by abundant epidota. Such a segregation was timid on tlie dnni]) kC tlie tnTincl nf the Star placer mine in Wolf Creek, a short distance above the Omaha mine, and eoDsisted of a eoane mass of epidote, magnetite, and pyrite, witii omsts of chabazite; it was asaayed and fimnd to oontafai 1 once of

A of fresh appearance was noted on a dump 900 ftat east of the Booky Bar deq ahaftb It probably ooeors aa a dike in the ])rcvaiIiog denser diabaaa-porphyrite whteh is filled with epidote and

Tiia prevailing rock at the Peabody mine is a fine-grained diabase. In the northwestern part of the area dark-green porphyrites, with nnnsually large white fehlspar cry.stal8, ap])ear.

On the whole, there is in this area no marked dynamo luetamorphism, bat an extensive alteration, reenlting chiefly in epidote, chlorite, and pyrite, and there is evidently no fHdsjiar formed. This alteration is distinct from the dynamo-metamorphism, but, on tlie other hand, it is also distinct ftom and surely not cansed by tlie thermal waters ibrming the quartz veins. Epidote can evidently not be formed by this thermal protects, and the alteration shows besides no dependence on the qoacts veins, not growing more intense aa these are approached.

Wmtkeriny.—Tb rot k in this area is deeply deoomposed and covered by a clayey, residual soil. The only expo.sores arc afforded by the mining operations. This zone of extreme disintegration and decompoaitlon is sometimes 90 to 40 ftet deep

Relation to other m A.— The contact ou the west with the Calaveras formation is not well exposed. Near the North 8tar mill a 12-foot-wide mass of silioeous and ja8])er}'' rock, reddish or yellow, and containing nests and cavities with chalcedonito, lies on or near the contact, bat of normal contact metamorphism there is no dear indication*

unamL} DI4BA8B AKD PfmPBTBRl OBOCTF. 73

Thb Osbobhb Hux Diaba8B, Pobpiitbitb, Usd Bbbooia Abba.

Sxtent. — This large area occaiiies a ooasiderable portion of the Boath-eastern

part of the Grass \'alley tract Beginning on South Wolf Creek, .southeast (f the railroiul Htation, it extends by tlic Empire and W. Y. O. I), mines aud tinally forms the great proiuiuent ridge of Osborne HOI.

Detcription of rockn. — The rocks are in general fine ;,'r;uii( d to aphanitiO| dark'green, aud the constituents can rarely be made out with the naked egre. WUle not generally affeeted by dynamo-metaaiorphism, the rocks are often deeply changed hy (ddoritie mod epidotio alteiatioD. fioth massive rocks and breccias occur.

At the northern end of the area, between the grauodiorite uud the Calaveras formation, the rook is a dark-green porpbyrito-breoda vlth

fragnionta of siliceous ar<,Mllite; it is hi-hly altered and lias evidently also been subjected to pressure. Films of chlorite aud secondary komblende obeenre the relations of the minerals. Seattered grains of magnetite and pyriteoecar in intimate Intergrovth.

Near tlie Empire and W. Y. O. D. the rock is very fine grained urailitediabase, at the latter place very rich in pyrite. The dark-green, finegrained rode ikmn the dump of the Golden Treasnre shaft oonsbts, In thin section, of abundant <;reeii iiralite in grains or ronghly outlined crystals, oontaiuing muetite aud pyrite iutergrown. The feldspars oonatitata an entirely bonded mass, once evidently fonniDg lath like crystals.

Vi-rv fine grained diabases occur in the vicinity of Houston mil. The Htructuie lu thin section, which with low magnifying power appears almost pilotazitio, becomes with higher powor very typical diabanc grannlar by long triclinic feldspar laths, between which He triangular masses, also anhedral or roughly idiomorphic crystals of colorless angite, undergoing a dhreet transformation Into chlorite. The titanic iron ores are transformed into leuooxene and pyrite, and pyrrhotite appears in connection with chlorite. Often there are large qnantitiea of nralite and epidotc and new-formed aggregates of quartz (and feldspar Y) containing amphibole needles.

A rock from near the 'nuiodiorite contact at Leeman's ranch, 4.000 ftefe east of the Omaha mine, is a durk-greeu, medium-grained rock of diabaaic appearance and containing a large amount of grains of pyrite. Under the microscope ftogreatly altered (-liarai ter is evident. There is no angite, but much brownish-green hornblende in irregular grains and shreds. An original mass of lath-like feldspars is entirely obscured by opaque aggregatsa of donbtftil ohaiacteTt probably in part kaolin. AUotriomorphic aggregates of secondary quartz, possibly also some new-formed feldspar, lie between the altered feldspars. Magnetite and ritfl in part inttniatdy intetgrown, are scattered through the ma—,

Diyilizua by GoOgle

74 aOU)-<iUABTZ T£IKS OF NEVADA CITY AND GRASS VAUJBT.

in the fr-hlRpar, the hornblende, ftod t!ie Hec-ondaiy quarts aggngatat; there ih ho vulcite. The rock oontaiiis a trace of copper.

Porphyrites aim ovcnt abundantly iu tbiB area. Northeast of the Bnpire hoistiii}; works, and 1200 feet distant, a greenish-gray rock

with STiiiill white fehlsjtar crystals wiis noted. It contains scatteml grains of pyrtt; one gram of ubulcopyrite was also determined. Under the mfcroeoope tbe etmetote appear breeefated; the fHigmente are of a porphyrite, the aiipito or liornblende boin;; converteil into chlorite. The groundniass is very annually fine grainetl, and haa a probably hypocrystalline, hyalopilitie atmctare, though the glass was not identified beyond doubt ; it may, however, have iMcoraedevitrified. In places the rock is amyrdaloid, the cavities being filled witli clilorite.

Specimens from a shaft on the Lincoln vein, due east of the Golden Treasnte abaft, show a angite-porphyrite; the idiomoirphie

feldspars are clouded by kaolin and strongly double refracting a;rgregates, iHi!<ibly of scapolite; the idiomorphic augite is nsoaily charao> terind by porphyritio twin lamellia. The gronndmaia ia hnlocryatalline and compoaed of small malice and ehnided feldqiar gxaina. Mnoii pyrrhotit is present, intergrown with magnetite.

The rocks from the southern end of 0.sborue Hill are generally grayiah-green, highly altered porphyTitea, with a atnmg development of epidote.

The summit and larger part of the eastern slope of Osborne JiiU is composed of a breoeia of differing eoareeneea, ebiefly made up of fragments of jxirjdiyrite and together with less of a gray or brownish, llintgr, sedimentary rock. Tbe feldspar iu tbe porplgr* rite is nsoaily altered to eipidote and other seoonda ndnarala, while the augit is ooQTnited to ehktite.

Weathering. — Over practically the whole area rests residnal soil of greater or \om depth, red cider, and clayey character, and the exposures are only rarely satisfactorj'.

Relation to other rocks. — Tbe brecciated character of the rock mass near the Calaveras formation has already been mentioned. Along tbe granodiorite contact the ex]>o.sures are not satisfhetory at any plaee, but dike-like masses of granmliorite in diabase were noted at many pliiccs from Little Wolf (Ji-eek .southward.

Beginning near the Orleans mine and I'xfending at least as far as the Daisy IIiU miuc are a series of dlke of ((uartzose porphyrite, occupying a plaee similar to that of tbe dikes from the eastern part of the Thinner Hill tract or some of the rocks from the St. John mine. This dike system probably extends farther south, as similar rucks are at thit Lafhyette tnnnel and other phicea on the western slope of Osborne Hill, but the outoroits are so obscured by heavy soil that it is scarcely possible to truce the dikes farther. liesides, the quartzporphyrite at the Lafinyette tunnel is less quartsose than that fiurther

Thk Ori.Kaxs Quartz-Porphybite Dikes.

Imphibolite Obodp.

nort)), and to grade over into normal A typical rock from the >'ew Opbir claim (140 G. V.) of liglit grayisb-greeo eoknr mad tsontains some epklote. The iirayish phenocryBts of ftldapw* M well a8 angite or hornblende, now converted into oUtuite, lie in denote, almost tlinty ToundniasH.

Tbe plagioclatso pheutwrysts appear, under the micrusco]>e, tilled with epiidote end mioMMOiw prodnetSt while the augfte or liornblende Ih ean-vetted

into uralile, chloritt', niid cpidote. The gronndinass consists either ot abort feldspar lathtt, between which lies a little quartz, as a eemcnt, or of a mieropoikilitic intergrowtb of feldspar laths and graiDS with quartz.

The rock was analUrzed by Dr. 11. Stokes, with the following result:

Prr cent.

Mo..

no, .44

P,0 &#x27; .14

FeO, 1 41

MnO Tnct.

BaO .11

C0 4.76

MgO ; S.15

K,0 1'. 7f>

a,0 3.47

HaO iMlew 110 C .29

i 100.41

The cotnpottition is almost ideutiual with the quartx-porpbyrite from the Banner Hill area, the analysis of wbieh is given elHewbere. Tiie relation of the quartZ')ior|>hyrite to the nurroanding diabase is

not clear at tliiiiiiiii ilike. but tiip inttu-<ive character is ajipareiit in tbe case of h Htuall dike of tbe Hume material outcropping in tbe bed of the ereek a few hundred feet farther down.

The Amphibolite Group.

DEI'INlTinN.

Under tbe name ''aniphibolite'" are here included massive or schistose rocks eompeaed ehielly of hmnblende, nsnally with smaller quantities <tf qnart?., feldspar, epidote, and chlorite. The.'ip rocks are here in most cases products of dynauio-metamorphic action primary igneous loeka of tbe onnposition of diabases or porpbyxitea.

76 aoLD-<)UAUTZ rmm of nevada city and oeabs tallbt.

Ths Ihdiah Vlax Akfhibolitb Abba.

JSvtenfThis anphibolite area really formt the northern end of Hm Plttsbarg diabase and porphyritn lielt. As the pro<>eBs by which the am[)hiboIit<>s have been produewl has in fact af!e<:ted all of the racks iu the belt uieutioued, it is uecesai'y to to some exteut the aUnratloii over the entire are*. It to very evident Ibat tlie ectrane mechanical (reformation causing whiatosity is not necessary for the prodactioQ of thoroagiily metamorphic amphibolitic rocks. The rucks desiotod "mpliibalites'' are ia geiiMal Mditotoae, though rarely very proniinently ao, and are not aepatated by sharp Una fkom tiie leas altered diabasic or porphyritic rocks.

Description of rockt. — The less schistose aiuphibulites and the uralitlaed diabawe are not readily dtotingaiabed by the naked eye, the fine ".'rained strnctnre and dark jrieen color being eonimon to both.

The tirst stage in the luetatuorphism cousiats in the uialitization of tiie abundant augite (and rarer hornblende) In the piimaiy rocks; at the same time the ends of the crystals feather oat in ragged and divergent aggregates of light-green hornblende, and needles of the latter seattor through the feldspars, it is not necessary, however, that this process ahonid be eomplefeed beAm the alteration proper begina. The latlw cousists in the forming of dear, allotriomorniiic granular aggregates of generally uustriated feldspars, quartz, epidote, with abandanl newly flmned green, frequently idiomorphic, hornblende and dark norm biotite; this hornblende should not be designatil "uralite;" the fonna assumed are well indicated in a figure of the Conrad tunnel amphibolite iu a paper on the Ophir mines.' Besides these minerals, magnetite, pyrite, and pyrrhottte are formed and contained, eqatvalent to the other components, in the secondary allotriomorphic mass. new-formed mosaic encroaches gradually on the original minerals; the remaining feldspars appear as rennuuita eloilded by mnscovitic miaerals and epidote. The eventual result is the conversion of the rock into an evengrained, clear, and fresh mosaic, an aggregate of t he secondary minerals.

Musoovitic minerals are not, as a rule, formed in this process, nor is chlorite, though subsequent alteration may prodooe them in tiie amphibolites. A'ery characteristic for tliis area is a Strong development of secondary biotite. That contact metumorphism has not caused this alteration is indicated by the ftaet that the black Mariposa elay-slates, easily susceptible to the intlnciices of that process, are not notably altered, while the sorroondiug diabasic rocks have been considerably changed. Toward the end of the area northwest of Indian Flat, however, it is possible tliatoontaet nctanuirplnani to in part reaponsiUelbir the alteration.

In the tuft'aceons rocks irom near the Herring reservoir the meta> morphie proeesaea are ataeady noticeable, Uralite largely leplaoea

ItMrtMMtk An. Sift. V. S. OmI. Samy, riHtll, UN, p. m.

Diyilizua by GoOgle

&#x27;I

Amphibchutb Obouf.

Mgite, and a reddish-brown mica deTelops abundantly in the nralite; in some crystals the tendency appears to be to convert the whole mass into biotite of similar orientation. Between the original feldspars, and also to some extent in them, the biotite is also developing, as well as abandaat needles of new amphibote (104 K. O.). In otiier speeimeoa (105 Jf. C.) from tlie same place new allotrioniorphic feldspar aggregates appear, forming with biotite and hornblende a clear mosaic. Pyrite and pyrrhotite, as well as some UaA iron ores, are also among tlie new* fbnned aineruls making up the being filmed eon* tenponuieonsly with the biotite.

Fnmi the Pittsburg mine down to Deer Creek the prevailing rocks are dark-green nraUtdiabases; Temaining kernels of angite often indicate the derivation of the light, bluish green nralite; the edge.s of the nralite are extremely frayel and ragged, and needles of new-formed iMmiblende paneifenito the feldspar. The original feld .s] turs are ekntded and filled vtth mieaeeoaa aggngataB and epidote; between them and in them new. clear nosaie aggrsgatsa are fimning of feldq;iar, Ikhii* blende, quarts, etc.

KovCb of Deer Oreek the altaiatkm Incrcnics; fha took I400 ftet northwest of the Indian Flat schoollionse is tj-pical flOl X. 0,). It is a ftne grained, very slightly schistose amphibolitt of dark-greeu color. In thin section the rock pnaents a blotebed from the oooov' venue of larger white spolsin the more even-grained prevailing mass Tlie latter is a ch-ar allotriomorphic mass of biotite and green hombleude in irregular but sharply defined grains and foils, with grains of new-ftnned fUdspar. Tlie wliita spots avs tba remains of larger plank> clase crystals, now and filled with minute lionililende needles. Tbe process by which this mass is converted into the clear mosaic aggra* gate is very well shown, the latter eorrodlng the older feldspars in all directions; RDinctiuH s the feldnpar is cut by veins of the nHWWifti In other rocks from this vicinity remains of augite are seen.

Toward the Oro Fino mine, beyond the area of the special sheet, the amphibolite becomes more schistose and moreeompletely recrystallized.

From the clear, fresh character of tlie new mosaic and the clouded and altered remains of older feldspar the couciusiou might be drawn that this alteration preeedea the Ibrmatlon of the new moaate, or, in other words, that the rock was already considerably altered before the dynamo-metamorphiam took place. This conclusion is, however, of donbtfril value, for the new-lbrmed Mdspar is probably albite and much more resistant to alteration tlian the Old aodalime feldspar. While deformations of minerals liy pressure are met with in these rocks, they are nut nearly so prominent as, for instance, in the adjoining aplitedike or in saadstonesof GiraasTallegr. Qnarti being most susceptible to crushing, rocks coiitaiuing it show nKMfl plainly the purely mechanical effiacts of dynamometamorpbism.

78 OOLD-VASTZ TBim OP NSTADA Cmr AMD OBA88 TAUBT*

THE UUCNSWICK AKEA oF SCOISTOSE POBl'UVlilTE BBECCIA.

Extent. — Begiauing aoatbeast of the Maryland mine, bordering gainst dialMM, thi are* extonda Mmtlieaatarly by tho Gold Point

and Brunswick mines, tidjuinid nn tlio iiorthcasr b}' serpentine and on the souUiwest by the andeaitic toff, to beyond tbe limits of tbe special map*.

Deacription of rock.—lh iwk OTMr the wliole area ia laOM m leaa

intensely iitlected by dynamo-metamorphism and has become Bcbistofle. At tlie Lucky uiine aud at the Bruuswick the suhistosity la more strongly developed, prodociog ampliibolitio and ohlontie flnile roeka. IeHS rocks (07 G. V.) occur on the road nlonj; the Gold Point ridge, atau eUn atiou of 2,700 feet. Tbe rock is a greemsb-gray, tinegrained brecc i ; i , ve ry bard and compact and roogbly sehiatose. Lighter gtagrish or browni.sh fragments of siHceoim argillite Hp])ear to shade over into the darker fragments of porphyrit*-. I'ndt r the microscope tho are sbovvu to be cliletly uugilic, with very Hue grained, partJy pilotaxitie groaadinaaa. A large part of the aoglte haa

been converted into nralltc. The cement of the breccia is a very confused mais of chlorite, epidote, white mica, and needles ol hornblende. Grains of pjrrrhottte also occur, mostly connected with chlorite.

Least altered i8 the augite-porpbyrite breccia from near the edge of the Grass Valley tract, 3()0 feet east southeast of the small Maryland shall ou the ridge (120 U. V.). It is a dark greeu, very hard, linegrained Toek of alightly fragmental aspect. A partial auidyaia of thia pnie hreecia, by Dr. H. K. Stokea, gaye:

The low percentage of silica and large amount of calcium in thia rook are aomewhat exceptional; the prevailing iUdapar mnat be of quite basic, character.

Weathering, — The surface of this area is deeply decomposed, the dark*red, clayey soil making the exposures, as a rule, very nnaatisfiuS' tory. At the Gold Point mine, 136 feet fi-om the surHice, the porphy. rite-schist is entirely disintegnited to a orumbUug yellowiah rook.

Per cmt.

CaO. KiO.. Na.0

is'.aa

Diyilizua by GoOgle

Chapter T.

THR StSDnOSNTAnY ROCKS OF TITE BED-BOOK BBBIBS.

General Features

The sedimentary rooks, coiisiHtiug ut° clay-slute argillite), siliceous argillite, quartritie saiiclatonet and chert, occupy relatively Bmall areas ill the tnicts described. Onlv rarely ;iii tlie stratificatidu Ik* r('( o<'- Dized, aud it ia then aboat vertical, aud approximately coincides with tbe nhiatoaity. The tatter ia always nearly ]>ei peiidicular, though light dip to the east may aometimes be reeogidxed.

Calaveras Formation.

liEI'INITION.

The CalaveruH t'urtimtiuu includes the Medinieutary rocks of Paleozoic age occnrrin); ill the Gold licit. It ia believed ou good grounds that most of this formation belongs to the CSarboniftfOoa, but it is possible that oliIiM rocks may also be present, the scarelty of fossils making idenUticatiou difficult.

In the areas referred to this Ibrmation no fimsils have been ftnind, and the evidence of a<:o is only cin uiiistantial. Tlie ImkIs an-altered, but not in general completely recrystullized, tltough,under the lutluence of dynamie and onntaet metamorphism, they grade into normal crystalline s<-hists.

The areas in tlie Grass Valley tiact are the continuation of the selinientary formatioiiM about Auliurn aud Colfax, in which a few fossils distinotiy indieating Tjower Carbonifbrons age have been found. The best locality is at Ilie old limestone ([iiarry '2 miles west of Colfax, from which .Mr. C. D. VValoott has ideiititied the characteristic corals Clisiophifllum gtUM Meek and LHJumtrofion whitneyi vnr. mi&farrb Meek, The areas in the Banner Ilill tract are the continuation of the aeries extending up by North and th' Delhi tnitie. in which masses of limestone with crinoid steins have beeu found along the South Yuba Blver, indieating at least a Paleosoio age.

These sedimentary nx ks are iiioie resistant to weathering than the granodioritC; and iu the liauuer ilill and 'evada City tracts form a ling of hOto rising like an amphitheater around the broad deprosstoin ooonpied by the gnuiodiorite.

80 Oouhuabtz Veins Ov Nevada City And Okass Valliy.

XBB vmaatAL abba.

iforX: <le*caption. — Th' Fedenil Lo;ui area con tain 8, well cxjwsed in thedeep canyon of Deer Crek, very peculiar sedimentary rock, black to dark-brown in color, very bard and dense, witb a iVactnre ranging ftom imperfectly couehoidal to splintery. Minute fn'aiuH of sulphides are abundantly scattered througli it. It on)}' rarely, and then in decomposed outcrops, shows a truce of scUistosity, but is in general entirely maoBivei. It looks mnch hke certain very dense prodncts of contact nietaniorphisni, nsiially called lioriifeIe iNlt the extent of the area outside of the special map shows that itsooeorreuce is not dependent on the proxmdty of the fpmiitic rocks. On the contrary, It forms an importAnt part of the Calaveras formation in the area of the Colfax sheet, beginning north of Golfux and extending, several miles wide and magniflcently exiiosed in the canyons of the South and Middle Vuba, np to the northern limit ot*that slieet, irbere it is eat off by igneous rocks. Within this area it becomes schistose in streaks, and then appears as siliceous clay-slate; it also contains smaller lenses of limestone with crinold stems (Sooth Tnba Canyon). This rock may for the present be called Kiliceoun argillite, the word argillito being used to designate a fine-graiued, clayey, sedimentary rock, whether schistose or not, which has undergone some alteration. It presents some similarity to the cherts of certain sedimentary series but it does not occur in distinct layers as the radiolarian chert fphthanite) of the Coast Ranges, nor is it, like certain other cherts, derived ftom limestone. A certain similarity to lydite (Kiesdsohielbr) is also noted, but it contains mnvh less sillcii than either chert or lydite. Ft is probably to be regarded us huviug been originally deposited asa siliceous clay, partly by the agency of radiolarian organisms, of wUeh tiieire are, indeed, imlistinet traoes in the rock. The metamoiphism which the rock has und<'rosie can not, as stated above, be n'parked as contact metamorphism, but is more likely part of the regional and evidently dynamic metamorphism which has alfaeted all of the sedimentary rocks of the Calaveras formation.

In the excellent outcrops along Deer Greek above i'ederal Loan, the blacksHiceonsToek isseen tooontsin indefinite streaks of lighter color, which have n general north*soatbdireetioii; this may be aibint remaining tnu'.e of strati lication.

A rock from the ditch oppo.site Federal Ian,aud 1,3UU tVet ti-oiii the contact (23 TX. O.), corresponds well to the above description; pyrrhotito is contained in minute grains and veinlet<.

Under the microscope it resolves into an extremely fine grained, aUotriomorphic, holoortalline aggregate of qnarts and probably feldspar. Very intimately intermingled with t iiis mosaic are small flakes of reddish-brown biotite, and tliere arc abundant larger and smaller grains of pyrrhotite, in all probability of contemporaneous formatiuu

Diyilizua by GoOgle

OALAVBRAfl FORMATIOH.

with the biotite. A little earbunacoous organic matter is bIro preaeiit The slide it dotted by a few small roand and clear spots of a coarser quart/ iiigregate. It is not impossible that these may be radioUriaD

The unaltered wall-rock from the Federal Loan mine (36 N. O.) is of

flimilar apiieuraiice, but contains a few .naiiia of pyrite, besides pyrrbotite and minute eams of calcite, noticeable ouly uiKiu treatment with hydrochloric acid.

Under the microscope it apiiear a little eoarser than tbefoekjoat described, and presents remaiits of a ehistic Ktructnrc by larfjer rontid<'<l grains of quartz or feldspar. The uiaiu mass is the same intimate mixtore of brown, In part idiomorphfe biotite fails and allotriomorphio quartz feldspar mass. The feldspar is not quite fresh, being in part filled with micaceous minerals. Most of the sulphides are undoubtedly eontemporaneons with the fbmiallon of the mosaic.

This rook was analysed by Dr. W. F. HiUebnwd, with the ftOowing xesnlt:

Amalji$i* call rvck/rom Federal Loan mint.

CaO

SrO

BaO

MgO

K,0

Na.0

U,0

P.O.

Co,

Carbon of orcsnio matter

H.01n1ow1IOC

Per CM t.

9S.Ss

S.47 Tnot.

LSI Trace.

I mUiU* mlpUd (te VtO oald aat ( I Sir HMIb la Murtid >Mk

The annlysia shows that Che rook is net n lydite or KieaslaohieliBr,'*

m it contains too little silica. On the whole, the eompomtinii is Himilar to that of many so-called lliilletliuta,'' although in the lattor rock the 17 OBOL, PT 1

Diyilizua by GoOgle

82 OOLD-QUABTZ VEDIS OF KBVAOA CITY AKO OSASil VALLEY.

origiual clastic structure is wholly Imt* It is too Mid, oo the other

hand, fur ati orditiiii v :ir;.'illitf.

Wmthtriny.—Oii the of the ridges this rock weathers to a white, soft, elay maee, rach as ie exposed along the road to Bootts Flat, 11 little cast of the eastern boundary of the sheet. The weathering is not, liowever, dtep, and the rock on tlie whole shows comparatively great resistance to this process. Bed soil, washed down fi-om the ajaeent masace of andeslte and porphyrite, usually covers the surface.

Contact mrfttmorphism. — For u few liiindred fcft from the contact the siliceous urgillitos arc altered to more crystalline rocks; the best espoenres are found in Deer Greek below the Federal Loan. The eonfcut is tfiiicly sharp, and twar it, as iiioiitioiHMl, a dike of fresh granodiorite (Kx-urs in the altered ruck. For the tirsl few feet fi oin the oontaet the sedimentary rocks are converted into aMdiuui graiuexl, gvarlslif slightly schistose, gneissoid rocks; the gain is of varying coarseness, and the nx-k jireseiits a spotted ayiprnraiice froni tlio irregular distribution of the biutite, occurring abuudautiy a8 kuiuII block faOa. A thin section 2 feet from the eontaist shows a coarse nuMale strncturo of cpiart/. and feldspar without twin sttiation. with a few roughly lath-like idugiuclase crystals and much reddish-brown biotito in straight Mia, in part altered to chlorite. Five feet tnm the oontaet the grain of the rock is already finer, and in thin section the mosilio Btrufturc of quartz and some not twinned feldspars becftmes more pronounced. Abundant small biotito foils and a few cubes of pynte are incloeed in the fiesb quartz grains.

For a few hundred tVct hack from the contact the rocks show a :rad ually diminishing grain until the normal structure, previously described, is attained. The typical contact racks of tills type are of brownish or brownish-violet color, fine-grained, but not flinty or splintery, and the blotite foils in them may be observed with the magnifying glass.

lu thin section these rocks consist of a fine-grained mosaic of quartz and feldspar, easily resolved by a No. 4 Hartnack objective. Larger foils of reddish-brown miea with irrejnlarly rounded otitlines lie between the grains. The biotite is partly converted into chlorite. In the dear mose grains are embedded a great number of small biotito foils, the larger hexagonal, the smaller with outliuea; magnetite, pyrite, and probably also pyrrbotite, are embedded mostly as small crystals in the fresh quartz and feldspar mass. The sulphides are witboat doobfe fined contomporaneottsly with the other contact minerals.

Thk Banner Hii.L Akea.

The sedimentary rocks occupy the northwestern steep slope of Bannr HilL Less altered bhuk argillitee of imperfectly sohistose diane* ter occur at tlic old RaiiiitT mine and in the small area south of the andcsite, while along the contact near the North Banner mine and up the creek homfelsor eontaet-metammrphoeed siliccons argilMtea prevaiL

Oocnpying the broad belt aoraaa the dammit ot Banner Hill ia a

Diyilizua by GoOgle

Calatbbab Pobmatioit,

breociated tone oontlatiDg chiefly of a baid, oompoot, Mid wellceiiu

Mitcd mass of an;;nlnr, fray to brown t'nifmpiits of tlie 8aiue rock tbat hati beu described m sihtxom aigillite from tho Federal Loan

Ll tliin sei-tinn the Iatt4*r ixwrk ap]>earA with it8 characteristic, extrcnidy tiiir> alluti iomor|)liic Htructnri', but with less biotite tliau near the i'ederul ; other fragments are uf igiieouM racks, aud are ideutkal with the aogite aod horablende porphyrites of tb atioining Banner Hill area. The aiiioiiiit of tlir ij'iieoiis franiicnts jradnally Incnaaes until uear tliat areii they prevail aud only occaiuuully gray or brown fragmentii of the sedinentaiy rocks appear. The igneous fraguients are generally well preserved and Show unaltered Iwown hornblende aud greeuiish angite.

Very characteristic of this brecctia is a reorystallization effected between the fragments and aim iu the sedimentary rock pieces. Allotriomorithic mosaics, soinetinies rather coarse, have been formed, and consist of quartz, possibly also soiue leldspar, with a pale-green, anbedral mineral wbieb fiom its deavage and eztioetione midst be a nionoclinic pyroxene, perhaps malHcolite, though the small sirs of the grains did not its positive identification; it is certainly not an epidote. More slender greenish needles in the same secondary aggregate are a very light green amphibole. With this mineral oombi nation is aasociateil abuiulajit ])yrrhotite, giving evidence of (b'rect connection with it by being surrounded by rims of the same pyroxenic mineral. This pgrtrbotite is thus not oonneeted with or Ibrmed by the amUbrons vn Bolations.

A qoartsitiu rock occurring at the head of Little Deer Greek oomsists of a wholly crystalline allotrioraorpbio quartz-Mdspar mosaic and abuDdaiit small grains of luonoclinic pyroxene. This pecnliar

metaniorjihisni of Banner Hill breccia is interesting, and its cause is not quite clear. It may be the result of coutact-metamorphio action of fbe porphyritc Itcan hardly be due to tbe granodkrlte and of dynamo-metamorpbism there la no indication.

TBS OAIMDA BILL AMBk.

Tho ridge to the south of Canada Hill consiHts largely of argillite, evidently the coutioaatiou of the lianner liill area, covered iu ])art by the andesitle flows. Over tbe larger part the exposures are very inwr, bat it is clear that the rock is not much altered. The prevailing rock is a black aririllite with mnch carbouaceims matter, weathering gray and white aud breaking in shelly pieces without clear schistosity. It is mnch sMIer than the Fetoal Loan rock, and does not have the splintery fra<-ture of the latter. Where tiie area narrows, near the edge of the Banner liill tntct, a vertical tichistosity about parallel to the granodiorite contact bns to appear. The original bedding of the rock is not clearly indicated.

Along the contact with the granodiorite there is a gradually iadiug contact zoueiif honifels a few hundred feet wide.

Diyilizua by GoOgle

84 QOLO-QUARTZ TBIHS OF HETAOA CRT AND ORAflS YALLBT.

Tiik Nevada Citv Arka.

Extent and general clmnu Ur. — A8 a narrow blt, from 4U0 to 1,500 ftet wid, and dotely following the grauodioritentmt, the Paleoioic rocks of tlif fdiiuation crow the Nevada Oit tract in a general uortbwesU'rly direction.

!nie Rwlift are generally very distinctly aehietiMe and oonwat of bloclc argillites or clay-slates, siliceous argillitea, and quartzitic and mieaceons schists. In the sotitheastern t a zoiio of coiitiw.t-metnmorpliic rouks, a huudieil I'cet wide, Iic8 next to the contact, whde from near the Providenoe mine northward tlie whole belt ia oompoaed of highly altfrtul schists, hut wiiethcr itll of this ihoold Im credited to tlM effects of contact metamorphism is doubtftd.

uf nwtt.— Black, more or Icaa llaaile argillitra ooenp7 the eastern of the area. The exposure* are very diabaae*por> phyrits, soiiip very rich in pyroxene, occur as detached mas.se.s in the slate, and siimllcr masses of slate arc embedded iii the igneous rock.

Good eacpoenrea are noted whne the eraek draininfr Flat craaaea the un'a. .lu.Ht south of the Orleans vein in tliin creek is a cropjiingof hail, brownisli, schistose bornfels, with alternating liglitcr and darker streaks, probably indicating stradilaition; the aehistosity is parallel to these and to the contact: ilie dip is 8.')' N. Flat Joints dipping east" intersect tlie Hchist. At Orleans shaft there are some p'leissoid contact metamorphics and black clay slate with knotty achiefhr). The contact metamorphiam extends only fiOO or 000 feet Kearer to the diabase, in the same creek, are fissile, dull black alates containing much carbonaceous matter and tinely disseminated pyrite; in these there is no indication of contact metamorphiam.

Near the road sonth of the snlphuret works there are otttcropa of fissile, weathered, knotty slate's of silvery-gray color.

At the Fortuna mine the contact metamorphism is not strongly indicated. There are black, booty, slightly knotty elay-slalea and harder ailiceons slates of a brownish color, a development of blotite.

Farther west the melamorpliism becomes more intense, and unaltered datea are no more seen. In the vidnlty of the Groeby shaft some highly altered <'ontact schist.s, streaked brown and preen, are exposed, while the dumps indicate that the sedimentary rocks ooutuin many diabasic dikes.

Bntwnish, highly altered, mioaoeoua sehists appear near the contaefe at the rrovideiice mine. The pood outcrops in the bliitV near the Home mine show a tine-graiucd schist streaked brown and green by alternatingdevelopmenta of hornblende and biotite. The blnlT is eat bj Joints dipping east and west at moderate angles, and the dark preeu diabasic rocks, not at all or very imperfectly schistose in places, cut squarely across the schistose sedimenUiry rocks.

On the opposite aide of Deer Greek, below the Wyoming mill, occnra

Diyiiizea by

CAIiAVVRAS PORMATION.

a (lark-brown, im{)ert°ec'tly tinile urgillite with a somewhat knotty surfiiee and Kbowiofr under tlw microBCope avery fine iniiined,anotrioiDoir*

]ihic Tiiass quartz, ft'ldsjmr, and biolite, with idik Ii carboiiacrons matter. iSomewhat scbUtose, dike-like masiies of ruc-k are oontained in this argrilHte.

On the dump of tlie Wyoming up|)er ahaft were noted dark*brown, fine jniiiipd. crystalline slates with macli pyrrbotite in fine disaeroini tion, certain .streaks being richer in bait mineral than others.

In Wood's Itavine, below the Nevada City mill, good esposoree aie fonml (if tine },'rained streaked greenish and brown, out by diubiUiic veins and in places coutaininf; small, lenticular, and pressed qnarts veins, possibly the result of an older period of qnarts formation than that to which the jtriMluctive veins lielonj,'.

From here on northward the rocks are principally fine-grained, brownish sehists, streaked brown, green, and gray, and often vlth homstonelikefltwtare; there are also some greenish amphibolitio schists, which nppcjir to represetit jiressed rock of originally diabasic chara< ter. In thiu section the prevailing rocks consist of line-grained quartz-fehlspar mosaic with outlined grains and ilakea of hornblende, epidote, and biotite. and often show a streaky appearance by the arraugeuieut of the latter minerals. TbiH rapid variation and the usually predominant biotite separate them from the slaty amphibolites on the west.

Frintinn to other rock. — These sediinentary rocks are distinctly older than the granodiorite on the east and tlte diabasic rocks on the west, both acting as intmsives toward the Oalavnaa abtea. Some of tlie diabiisic (likes show relatively slight alteration, while others are converted into amphibolttic rocks. Whether this is dae to a did'erence in age of the latter or to diUMng intensity of the dynamo-nietamorpbie action is not certain.

The schistosity is in general parallel to the granodiorite oontactt, but from this the conclusion mnst not be drawn that the pressure from the intmdve granodiorite has prodaoed the schistosity. In details, snoh

as in the cxposnrcs in the crosscnt on level in tlic City mine-, it is shown that the granodiorite cuts across the schistosily, which evidently was as strongly present at the time of the intmsioD as it is now. Kodonbtthegrauoiliorile has exerted a strong pi-essureon the schist masses, bnt it has mainly a pushing and bending action on the already formed schists. Toward the Coan mine the scbistosity makes a ditiuct angle with the contact line.

Till' (]Mf-ition of how far the nlti-ration of the slates is dnc to contact metainoi pliism is an obscure one. To judge from available evidence from other parts of the special maps, the oontaot-metamorpbotttng action has not extended beyond distance ot a km hundred or a thoa* saud feet.

86 Oold-Qvastz Veins Of Hevaoa Cxtt Akd Obam Valley.

Tbb Oba88 Vallbt Abba.

Oenernl Hmrrtpiion.—Thl of sedimeiitai y rorks, 1.000 to 2,500 feet wide, exteiidM ncmmi the nortlieatitaru part of Grass Valley. To the northwest it exteiuls niider the covering area of andesitic mntorilllf M indicate by the duiiip at the vhHoua shafts aloiir the Alta channel. To the southeast, it also innhalily eoiitiiuif* itiulei the aiidc- Wtei, OH iiidiciited by the Htnall ui'ea iiorltieutit and of the EltH-trio mine. The oatrroin are very unmtisflictory, and oooBlat chiefly of a giavish, uiediuin to ears praiiied, qiiartzitic Randstonc and a very carboiiaci'ouM clay-slate. The former is characterized liy many grama of dai-k pray qnnrts. Near the granodforfte' harder, dark-brown, contact metiiinorpliic rockH apiiear.

Fresii rtx ki found in tlio Kiireka Crown Point mines look very dilterent. They aio hiird, black, iiiart/jtic huiidstoues, eouiiiosed chiefly of ainallf clear grains of quartz and similar black argillitec with imperfect cleavagC) breaking in irregular fragments witli smooth, ;.'Iistelling .surfaces. The argillites contain many larger clastic ft-uguieuts, chiefly of quartz, and both rocks contain pyrrhotitein great abundance as gfttinsand Heanm with quart/. A little crystalliue limestone of dark

color wa.H found on the New Knrek;i <luinp.

Microscoinv tUm ription. — Under the inieroscope these rocks present several intereMting featores. The whole series apfiears extrcsMly afl'ected liy dynamo inctamorphie action, most intensely manifested in crushing and IriKrturing. The clay-slates are com>>o8i'd of very fine grained aggregates with abnodant newly Ibrmed mnscovite, sometimes biting into tlie quartx graiiiR, and much carbonaceous gnbstanee. ▲ few larger eruslie*! elastic grains were noted. Kxtreme crushing has practically converted soine rocks to a breci'ia, traversed by small white Teins, described below. Others show a pressed stmctore paiallel to the cleavage, and some clastic ;;ruins are elongated in tilCSamc dircctioil. Grains of pyrrbotite are very abundant throughout.

Still mom intcratting ate the quartzitie sandstones (72, 73 O. Y.). Tlie cliistic grains are chiefly quartz, while some feldspar, in part with twin lamelhe. isalso present. Carved lines of fracture and small veins, chiefly of caicite and quartz, traverse the slides. The cement is xecrystallizcd into an irregularly intergrown aggregate of quartz and feldspar with shreds of biotite. mnseovite, and chlorite, ryrriiotitc also enters into the com])osition of this new-formed mass, and cousidcrable organic matter is present. A few crystals of bluishgray tourmaline were noted in the cement. The clastic grams are extremely pressed, and crushed to lentienlar masses, showing all gradations between undular extinction and complete crushing and recrystaUization to a flner aggregate. liesides, the newly formed <piart/ feldspar mass between the grains is vitrorously corroding the clastic {grains and converting them to a Uuer aggregate. There is here au excelluut liiustiatluu

Diyilizua by GoOgle

OALATBRAS FOBMATIOir.

of tlie ititiinate cxinection of dynamleal And ehemioal prooeMM in the recrystallizatioii of rocks.

A speciuieu from the Kew Eureka shaft, 200 feet down (343 Nevada OoaBty asfmilar black quartzitic sandstoue (tccarringai u small mass in .serppntiiio, shows in addition the small qtiartzo96 veins a oecuud liet of fractures, crossing tlie former and tillixl with aerpeotine. The aerpentiDe In places extends Into tbe claatio lUdapar and quartz };raiu8, corroding tliem in such a way as to leave no doubt that a liHtal seriK'ntiuizatiuu has Ueeo iu progress.

The feUhpothic pyrrhotite vin. — In the description of the Crown Point mine the occnrreuce of a very remarkable vein is mentioned, consisting of pyrrhotite and chalcoiiyritc with ealcitc and very little quartz. Tbe sulpliureta are lucid to contain some golil, while of free gold there is practically none. The psrrrbotite contains only a traoe of nickel. This ty|)i is so ally diffeiont from tlie trold qnarti! vein that it must be oousidured iteparately, uud undoubtedly has been formed niider diffierlng conditions.

The and slides of the black argilUte Arom near this vein, and also from the New Kuroka slit't. coTitain a innnlnT of small white veinlets, occasionally widening out to larger bunches of the same compact white material. Small graina and streaks of pyrrhotite and copiicr pyrites occur on all these seams, and in mic insfaiicf a little xincblende is probably also present; beyond doubt, the veiu near the Orown Point is only a large r representative of this tjrpe.

Under the microscope the veins are seen consist nf quartz, calcitCf and a plapioclastic feldspar, generally ciouilcd and souiotimes showing polysynthetic twinniug. A small fragment of the feldspar was determined by Mr. George Steigerf by a qualitative anaiyais, aa aoda-lime feldspar apjroachinn labradorite, the fusibility aNo airi'being with tllla result, lu one veiulet (343 Nevada County coUectiou) the feldspar occara as small doomed prisms, between which lies dear qnarta. lliia is the only occurrence of feldspar on mineral veins thus far known from thia vicinity.' In the normal gold quartz veins they have not thna far been found. The largest veiu in the Crown Point mine shows no feldspar, but abundant light-green radial aggregate of chlorite, alike in the caloite, the quartz, and the pyrrtiotite. This ia also nnknown from the normal quartz veins in this district.

rodfct.— For a diatance of about 200 foot from the granodioritc contact dark brown, fine grained, quartzose, horufols-like rocks appear, showing but little schistosity. In thin section a few larger clastic grains of feldspar and qnartz lie in an extremely Ane aggregate of the same minerals containing, besides, flakes of reddlshbrown hiotite and 'i ain< of mau'netite and pyrrhotito. matter is also present. In the smaller area south ol Soulli Wolf Creek normal

'Mr. H. W. Tvri>*r baa reoognlMii alMU famUnn wilb quarts in a ahatlerad tama la an alWlo-

Diyiiizea by Gopgle

88 Goli&gt;-Quaktz Veins Of Nevada City And 01088 Valley.

sandstoiips appenr iti the eastern part, while the part adjoiiiinfr the diabase is a liiie-ruined brevisiu of tliiti same bornrels-like rock, 8ome> tinea with fhignenti of porphyrite, and on the wbole very aimilar to the Banner Hill breecla. Some of the same characteristic <iurtrtzaugite mosaic oconra in it, the latter mineral being here ideutitied beyond doabt. Acoordinir to the beat evidence available, the rite is earlier than the i;ranodiorite. It is imssible that the imrphyrite in foriniiifj tliis brccf'ia — wliich must be considered as a oiita<-t breccia — has had a contact-iuetamorpbic effect similar ti> that oi' the granudiurite, fhoogb probably leaa intend. In flies, there ia eone evklenee pointing in the same from the (lold Flat diabase area (Nevada City 8beet)| for that rock often cuutaius fraguieiita of sedimeuttuy rocka in whidi m rimllar development of aeoondary biottte baa taken ptnoeb

Qumrts tourmaline rock.— In the porphyrite adjoining the gnnodiorila Jnat west of the S<()tia shaft are poorly masses of a array qoartzi tic rock wiih dark gray Hpotaatid blotches, in thin Hectiou this rock oonaiata of an allotriomOTphIo moaaie of quarts la which lie maaaea of greenish-gray tourni;dixie, with nnighly radial structure starting from a center of darker tourmaline. The ends of the tourma* line eryatala grvw into the quarts grains. This look ia regarded as oontaot-metamorphoaed qoarttite.

THB HOBTH aTAB ABBA.

Adjoining the diabase there eztenda along the western margin of tiie

GrasH Valley tract an area of sediineiitaiy rocks. The exiHianrSBi aS a rule, are very obscure. The area up|)ears to oon8i.st of large ledges of a grayish chert, separated by bburk, imperfectly fissile argillite, weathering gmy and breaking in shelly fragments. The chert is in places almost pure hydrated silica, and little vugs with quartz crystals. It is very ditlerent from the siliceous argillite from Federal Loan.

Ahmgthe poorly exposed contacts witli tlio fjranodiorite and iliabase there is not much evidence of contact nietamorphism. Ho special ezaminntlon has been made as to the origin of the ehert so abundant in this area, bnt it is suggested that it may be derived largely limestone by a process of siliciticat iou, such as has often lu en noted from other plaices in the Gold Belt, ihis view is cuntirmcU by the ocenrreneey on the top of the ridge nortliweiit of lortli Star, of a bowldepression or pit several hnnilii il fi-ct in iliiuneter, and which can not be explained except as a coliapsetl iimestoue cave. It is iudicated on the map as Devils Pnnch Bowl."

Mariposa Formation.

The Mariposa formation embraces the u|)])ermost part of the Jurassic, and Is oomposed ehiefly of a aeries of ohiy-slatSH. During the mi4ping of the area of the Smartsville sheet the extstenoe

Mawpobk Fobmation.

of ttie JnnialoMftripoMriatM, which wnthof OdAa are sncli aproml*

uent feature of the footlilll geohtgy, was not recognizwl. nor liavc any fossils beeo fouotl during the detailed exaniiuatioa in the rocks referred to this dlTMon. Tbo evideaoe along other lines is, however, so atrong that there can be uo rejisouable doubt that tliey are present.

The main of the Mariposa .shUen cimIs a short distance north of Colfax, being cut oil by igneuuH rocks. The slates near Colfax are identified by the occurrence of sevenil oharacteristiu types of ammonites.' Litholopically tliey aro charactpri/ed by black clay-slates and an abuadant development of jiorpbyrite-tuffs. About 7 miles north of Col&x a small streak of black taflkweoas day-shitea begins, and, extend* ing under the andesite table, appears again a short distance east of the Washin};ton mine on the headwaters of Wolf Creek. Ilere the series quite extensive and consists largely of tufiaceous fissile slates, appareatly gradually going over into bieccias.

A short (listance northward the slates are roiihu-ed breccia, but appear again iu characteristic form near the Murrimac inino, on the dump of which freah, black, tnlilMeonB slatea are wpoaed, containing, as seen under the micmscope, fragments of difTtTciit kindt of porphyrites and of the brownish, siliceoas argiliite, entirely similar to that of Federal Loan, in an argilhtic, very donm eement with mneh organic matter. The fragments do not show any evidence of consider, able ]H(>ssure. The alates near the mine contained much pyrite in sharp cubes.

The black day-dates can be traced norlhwaid as a very narrow

band, exposed in places by tiiniicls and ditches, until the excellent along Deer Creek, meutioned above iu the description of the Pittsburg area, are reached. A short diataocc north of Dear Creek the belt ends. On the hill north of Deer Creek some sitioeoiu argiliite is exposed, besides the normal black, very fissile, and comparatively little altered elay-slate. A narrow isolated area of block day-slate near Indian Flat has also been referred to this formation. Beyond this point the Mariposa slatea have not been found.

The relatively unaltered character, the associated and interstratifled porpbyritic tuffs, and the occurrence of Uragments of the older Calaveras formation arc the evidcuces indicating beyond reasonable doubt that these rocks are younger than the Paleozoic; formations. Through, out the area a steep or vertical dtj> prevails, and the schistusity cdnddcs, approxiuatoly at least, with the stratificatioo.

AHvMndM mUM mxI Undtrml. A. BjnH, TriM uA Jan 1m the WtMn StMMi BdLQMl 8a.AB.,VaLV,UMi.p.llCw

Diyiiizea by GoO'

Ghapt££ Yi.

Metamobphic Processes.

GMiifr to the word metanorphimn a Minrbiit wider sense tban that

in which it commonly it may be dt'liniMl as auy transforuiHtion in the iuiiieralo{,'iciil composition or ofarock, witli or without addition or subtractiun ui' substuace. This traiislbruiatiou cau be brongbt about by diflbrent agencies and with widely diflbring raealtn. The term mctasoiiiatism. or metasomafic action, is usually cnijildycd to designate a change in the cheujical as well as the mineralogical couipositfon, involving addition or snbtraetion of rabstauoe.

Ucstrictiiif? the wider definition of it is convenient to cxcliiilc from it the superficial wcalheriiir and disintegration, produoeil chietly above the ground water level by the actiuu ot atmospheric waters carrying oxygen and carbon dioxide. By tbis process there is not only a niiiieraloitrieal transform:! t ion hut tlic rock as sucli is The products of this process are, besides soluble salts, chiefly silica, ftrrie hydrate, carbonates, and kaolitt. Prooessee Uke cementHtion, or ofldinary hardening of fuift sedimentary rocks witboat extensive iniu> eralogical or stnu-turd change, are likewiHe

Large wetaiuurphused areas are often of as atl'ected by regional metamorphisni, a general term not designating thecaase of the action. A larfje part of the Sierra Nevada may tlius said to have been 8nb- Jevted to regional inetautorphisui. The main cause, however, undoubtedly being orogenie piesenre, tbe rocks are reformed to as altered by dynamo uietamorphisiB* Strictly spt aking, this term refers only to the purely dynamic proccises of crushing and shearing by compressive trees distrfbnted evenly tbrongb tbe rock or relieved along certain plaues. A sti ctrliiii;: !u;tion produced by a tensile stress ha.salso been recognized by several invcstijratoi s. but no evidence of its existence cau be said to have been louud during the examiuatiou of the rocka in this district

While examples of (dynamo-metatnorphism without extensive mineralogical alteration o('t;ur, chemical forces are nearly always involved and very generally play a moet important part, incited by the increase in temperature aecouipanying the pressnre at points far below the surface and aided by tlie of the rocks. It 18 not at all probable, however, that the heat during the dynanio-metamorphic processes in the Siena Nevada Imw exceeded a few bnndzed degrees centigrade, and of w

'1

Mbtavobphio Pr0Cbkb8.

ftisiou there is no indication at all. It is not necessary for tbc initiation of the recrystalliziiiiT action that the pressure shonkl have been carried to a point at which the limits of cohesion were reached and 8cbtotMe Btmctare produced.

Tlie process should perhaps niorci fittingly he dosipnated tlynamochemical metaiuorphism. It generally is character by a very modente liydration and tlie fiwrnatkm of elear, ftesh aggregates of mosaic structure. It iiaaally producea a rock of finer texture tlian the orip;inal one. Ifjiieons and stMlimentarv rocks are similarly utTecfed, though the ultimate pnxluctH uuully hitler. The chemical cowpositiuu of tbe rock does not appear to be greatly altered by tbe process.

Dynamo chemical metamorphism, best illnstratwl in this district by the Indian Flat aniphihohte area and by the Grass Valley Calaveras slates area, ordinarily produces tbe following minerals: feldspar (probably very largely albite), quartz, hornblende, biotite, muscovite, chlorite ( f"), cpidote, titanite, magnetite, pyrite, and pyrrhotite. The original feldspars are converted into albite, epidote, hornblende, qnarti, and mnsooTite. Tbe pyroxene lUters to uralite and reerystallized hornblende, biotite, and epidote. The larger grains of clastic or iMirphyritic character are not only crushed but also resolved to secondary aggregates by a oorroeively aetiag process of snbstitntloa, the new-formed minerals projecting into the primary grains.

Another and extremely prevalent form of metamorphism is apparent in certain rocks, such as tbe North Star and Osborne Hill diabase areas, which have certainly not been subjected to notable dynamio action. This jirocess, characterized by the formation of confused mineral aggregates, not so much by clear secondary mosaics, and by a moderately extensive hydration, mlgbt provisionally be designated WmnuiD hj/ilro vu tiimorphismJ The process miiy evidently be begun and accomplished at a comparatively low temperature and dejith under tbe influence of tbe moisture the rocks below tbe ground* water level; the results imply that these were waters not oxidizing and which contained no great amount of carbon <dioxide. As the depth increases, the character of the nietamorpbiam will naturally change by reason of inereaMiiig temperature aud sfeatle pressnre.

The minerals formed are chlorite, serpetitine, hornblemle, epidote,* moHcovite, probably also scaiiolite; further, magnetite, pyrite, and pyrrhotite; also zeolites. Seenndsry Mdspars are apparently not formed in this process. Thenriginal feldspar alters to epidote, musco* vite. and scafjolite; the augite to bombieudei epidote, chloritei and ])_\ritf: iliiM'iiitf to titanite.

>AUmt i-<|uiv,ili'iit to Uitth'H 'rntitplii irtr' Vprwitl-riiri::

Fpiiloti' rnnlain* mninl.T rirrii imn. anil 'I IuimMs |mi,hi Ii].' t ImI ir i mi li.) ' Uim ii foriMS nSW trni;nly nnlm-ini: fiiHurn<*<ii. Il howi-\ r, n-'t inN'i-.siir\ tit mijuMr'o that it must tiuvolMten forniMl uiiili*r iiilliiciKfH, Un rni kp i.nl . n n! v ronlaiii ii cciiiAtilrrmbU quantity of fniTic oxiile. rlir hill iiKi'ii lu'i-ii obwrvMl I'lnlmldrtl in li iliwit not worn Mrotaibto Unit it can be fonnad by >uri'*ci' uri-attfriiiK nntr orJl—iy tmrnftnlm moA fwiow. llMiftrt 0 T BiBttr. Mm. V. ML Gaul. biirvi>. Vol. Ill, p.Xll.

92 Gold-Quartz Veins Of Nevada City And Grabs Vallby.

Oikof the principal differences between this process and dynamo* chemical luetamorpbiBm in the absence of the secondary feklqpar and the momio aotore. It is dear from the above that, as the mineral series of the two pioi s overlap, there must frequently be great dilticulty experienced in (listen;,'uirthing thcni, and tlie processes iiuiy iu lact gradually merge into each other. Many of the products ut' the hydro-metamorphism have formerly been regarded eauaed by aoT' fiu'e (hM oinposition or weathering.

Another form of hydro-chemical alteration in which hydration plays the most important part ia aerpentinizatlon, by which certain barie igneous rocks rich in magnesia may, over large areas and to great depth, be transformed into serpentine. Being an essentially deepseated process, serpentinization should certainly not be referred to weathering.

Still another form of rhemical altenitiiMi is that effected by thmiial ascending waters, and which may conveniently be designated hydrothermul melamorpkUm. The results of this may vary considerably according to the composition the waters. If jra.'irons roiiiiMjnnds of sulphur associated with aqueous vapor are the chief agents, it should be referred to as $olfatrte mttamorpkUm, Under certain conditiona the hydro thermal nietamorpblaiB may almost indistinguishable from the ordinary hydro ( htMnii-al process, which indeed is to be expected.

In the case of the gold quartz veins here deiicribed, the waters were rleh in carbon dioxide and aalpbnretad bydrogen, and the chacaQteciatie re.onltfs of tbc inteoae metaaomatic aetfou are oarbonaieai mosooviteai and pyritea.

Finally, by another traaalbnnatlon certain rocks may reoryatalHae

when in close proximity to hot, intrusive. Igneous magmas, principally those in a state of aqueous fusion. This is eontavt metamorp/nam, and its products are generally characterized by ttie same allotnoniorphic, granular, ftvab mosaic aggregate which characterizes tlie dynamo* chemical ])rocesses. The initienils formed are feldspar (duerty albite), quartz, biotite, hornblende, pyroxene, andalusite, wollatonite, magnetttC) pyrrhotite, and others. While the dynamo-chemical proeesa tenda to produce flner grained aggregate.s than the oriiuial nu k, contact metamorphism usually makes the texture coarser; this is illustrated by the contact near the Federal Loan mine. Nearly all sedimentary rocks and tuflh, aswell as igneous rocks with a fine grained gronndmaaa, are subject to this alteration close to the contact, wliilc coarser frained igneous rocks appear to be but little atl'ected; this is by the ocearrence of frMh diabase close np to the granodiorite contacts.

The ]>roccsses here are doubtless the must inqwrtant ones, and each is in its way distinct and characteristic. iStill, many places occur where it may be donbtfhl to which of tbeae eanses the effects observed are due, and especially difficult is the task when, as often ia the oaaei, several kiuda of metamorpbiam have aoooessively

Mbtahobphic Processes.

9S

aflbeted the nKiks. Anions; tlicse cimes miiRt be counted tlw of tlio I?aniier Hill breccias, with their abaiidant ])yrrhutite and uew-furnjed of quarU aud a mineral btruugly reaemblinf pTroxene.

Alteration Of Feldspar In The Rocks By Hyoro-Chemical

Procb88B8.

The orthoclasc is, as a rale, far more resistant tban tlio phigioclase. When it is alteml the jjrodurt is ni'ticrally a wliitc sciicitic miisctvite. to calcite bus not beeu uberved except iu tbe viciuity of fbe veinfl.

The secondary in-odncts in the lime fehlspars may be of diflVr eut kiuds, aud, ou the whole, those feldspars are very readily altered. Horablende and epidote freqamtly develop in them; also, to some extent, biotite. Tbe basio feldspars (f the 'abbros often break pinto fine-trained saussiiiitic a;,'{rref,'ateH of zoisite and albite, but this appears to belong in the realm of the dyuauio chemical processes. By flur more eomvon, however, is m nltenitioii to prodocta wMoh very maeh resemble seririie, and tlie presence of this or a closely allied mineral can, indeed, in many cases be proved, even when the ortlHx la.se iu tlie ame slide is not attacked. This is eertafnty enrloaH, but, as is wen known, Lemberg has shown by his analyses of plagioelaNes that, as a matter of fact, the final is oft<'ii rich in jiotasHinm. In many other cases there i, however, considerable doubt whether the new-lbnned mineral really ia sericite or not. Being in very small por tides, it is ditlicult to determine. The fraction is low and the double refraction strong, though not so strong as would bo in muscovite, and it is suirgeBted that the resulting mineral might iMssibly be srapolite, a mineral known to occur as a product of alteration of feldsparn. An extensive kaolinization of the feldgjiars has not been recognized, aud probably does not occur below the zone of surface weathering.

Tbe only extensive (fC( of a kaolin-like mineral is that ia tha rhjoUtic tuflii meatioued below.

Occurrbmcb Ahd Pormation Of Iron Boiidbs In Thb

Rocks.

General features. — Too little attention has been paid to the occurrence and genesis of pyrite aud pyrrhotite, so common in the rocks of many districts. For the stndy of mineral deposits this subject has the deepest interest, and it amy therefore be of some value to summarize the results attained in regal to this during this investigation.

Pyrite and pyrrhotite can be tormcil many different ways, in fact by any of the processes above enumerated, except by weathering under ordinary atmoapherie inflnenoes.* And still the pyrite inthe rooks,

reducing uiflueooMk

Diyilizua by GoOgle

94 Gold-Quabtz Veins Of Nevada City And 0Ra8S Talley.

wiitni iiK Titioned nt all Id dcaoriptiwia) is often refined to as a prodnet

of wvatbcriug.'

Produel* of magmaHe wiuoiidaikm, — Pyrite and pyrrbotite may both

be fniistituciits of intiiiiatic consolidation, (.'ojfeiit proof of this is, of course, diflicult to bring, antl tlie fact Imrdly yet quite universally recoguized. Tbe case recently by l*rofvii8or N'ogt from Norway and tbe figures given bere (figs. 2 and 3) from Grass Valley diabases leave, no room for doiiht of primary origin. Besides tlie excellent occurrenceti iu tbe Maryland and tbe Nurtb iStur diabase area, tliese minerato bave been so frequently found in other roekn, ebiefly diahasic or poipbyrif ic, iimier eireiimstances which strongly suggest, tbongh not positively prove, primary origin, that the proposition may be confidently advanced tbattbere are, as a rnle, accessory primary constituents of the rock. As distinct traces of cop))er have also been found in one of tlie above-mentioned trt sh nx-k-i. it iii;iy be aa probable that cbulcopyrite also occurs as a primary constituent.

Prodmeta of eoiUnet mettanorpkUm. — Pyrrbotite bas been reoofnised as an integral piirtnf tbe a1 lot r'omorphic aggregates pmdneed by OOntaet metamorpliism (Federal Loan area).

PtodvcU of (dynamo-dtemieal nteUtmorphwm. — In tbe metamorpbio rocks produced firom igneous and sedimentary mati-rial pyrite and pyrrbotite have been observed as unquestionable constituents of tbe newly formed aggregates (Indian Flat ampbibolite and Grass Valley quartzitiu sandstone). latergrowtha of magnetite and pyrite axe fteqnent. In certain anipliibolitic schists iu viirious starts of tlie Sierra Nevnda l;u fje quantities of pyrite and chalcopyrite bave beeu vuuccutrated by these dynamosbemical ]irocesse, forming tbe ezaet equivalents of tbe fireqaently described fablbands firom other of tbe world. It would seem saitable to reserve the designation fahlband for sulpliides formed Insebistsby dynamo-chemical processes, thus not including in it schists altered by snbseqnent action. These firiilbands sometimes apiiear fo contain some silver and a little gold.

I'roiluvU of common hydro metamorphim. — Both pyrite and pyrrbotite bave been developed abandantiy in roclcs snbjeeted to hydro-metamorpbism, and a little ehaloopyrite lias also been noted frequently. Developed in this way, tbe association with chlorite, as well as with epidote, appears characteristic While tbe pyrite may occur as sharp crystals, it is more common to find it in anbedral grains often surrounded by chlorite rims, Tyrite atid pyrrbotite often occur in intimate inter with muguetite, and also tilling Meams and forming smaller segregated masses; pyrite and epidote are often Ibnnd intergrown In this last-named manner.

FroflucU of hydro-thermal s. — Extremely abundant is pyrite in tbe metasomatic rocks accompanying the veins and formed under the

U. H. Wllliaroa, Tli<.> arbUt aroma of ttieMeoumioeciuid Mjtniurtlereglitiw uf Michigan:

MBTAHOBraiC PB0CE8SE8.

influoiK'c of vt'iii solutiniis. T'\ ri !iotitf> iievrr rxTurs. wliilc arsi'niiMl pyriteti may be loruied. Magnetite appui-eutly can not bu ioriued under tbe eonditioDS preyailiDg in tbis process. Idiomorphic form, as sharply defined cubes, is most common. A iVeqiMOtly available criterion fas tlie idMitififation of tlic of tins pnxjoss is the narrow rims of cuUtite or quartz Kurruundiiig tbe crystals. Large often occur developed porpbyritically in roelts wbicli have not otherwise been subjectt'd to very intense hydro tlicriiiiil and do not disturb tbe grounduiass or crystals iu wbicb tbey aro embedded. The process must be regarded as entirely one of snbstitntion, or dissolving of tbe origi* nal substance and deiMsiting in its Ktead tho pyrite. The pyrite develin this way is ppnerally contiiiod to the vicinity of the vein. Larga areas are not in this disiriitt allectd by hydro-theruial processes.

The ease of Ibrmation is in tbis case undoubtedly the action of the tiulphnretcd liydro-en or alkaline sidpbides in the water on the silicates and oxides uf iron iu tbe rock.

In many eases, eeitecially where several alterations have been superimposed, it of course extremely diflienit to deHignate the exact mode of orin of the pyrite and ]tyrrhotite, but in typical cases these five modes of formation may be cleurly disitiuguihed.

In the last case there has clearly haen an addition of sulphur to the rock; in dynamo chcinical. coittact metaniorpliic, and ordinary liydrodiemieal processes it is not clear that any such addition has taken place. It is, perhaps, rather to be regarded as probable that the snl phldes have resulted a concentration and recrystallization of tbe sulphur and tbe iron primarily contained both in sedimentary and igneous rocks. On this point it is, however, not easy to speak definitely. By preference pyrrhotite seema to fbm in the presence of vary strong ledndug influenccB.

Under the above name are indnded clianfips in cohesion and composition wrought in tbe rucks umv the surface, chielly by the decomposing and oxidising action of tbe percolating aurfisce waters, partly also by tbe change of temperature. Most intense at tbe surtacc, the aetioa gradually decreases downward, and, in most ea.Hos, practically ceases when tbe level of the ground water is attained, which suggests that it ia largely due to tbe carbon dioslda and oxygen contained in the snrihce waters. The processes result in two zones, nionot less injperfcctly separated: First, tbe deeper and more extensive part iu which incipient decompoeition and hydration produce a disintegration ; tbe rode beeonMS soft and enimbling,but the chemical composition is not greatly altered.* Second, a surface zone of extreme and oxidation, reanltinff in the formation of a residuary soil.

'Thix fart ha* Ix-i-n broth)!ht out m-viiUy by Prof. O. P. Merrill In bk* (tudle* on Uia dMOBpOlMlaBcriMlwi Bll.GMl.SM.AM.,VLVI,MM,pbMlt VtLVU,mt,p.m.

Wbathbrimo.

96 GOLD-<jUARTZ VBIN8 OF NEVADA CITY AND GRASS VALLEY.

In the districts here described nearly all of the rocks are more or less deeply affected by those processes which may together be described by tbe not very apt expresskm **WiMitbering.'' Deep-red reeidaary soil covers large areas, and the dnategration is sometimes fiNind to extend to a depth of 2110 feet. The granodiorite, the diaba.se, and the porphyrite, ill some pluceii ulsu the audesite, are deeply aHectedi while the erpeotiiM, fbr iimlnee is far more xwiataDt to the weaClMriDg toflaeuces. The foriiiutioii of sm h minerals as epidote and chlorite is here not considered as being due to the weathering, but to deep-seated proeeuee. More detailed notes are found in the description of the dlflteeut weM.

Chapter Vii.

This Sufebjacemt Fobmations.

While it is not intended to treat the Keooenedepoeits in detaQ in this jfKput, their general character may be brkAy indicated.

Aurifbrou8 Oravblb.

The uuriferoiis gravels proper, reHtiiig directly on the Hnrface of llie hed*rock mricfl along the depressionH of the Neo<-eii rivers and ereek 8, consist, in f1u> !iir;:er cliaiiin"!-:, of well roninU'd pehhlcs of (juartz and harder ruuks of the bed -ruck between which hc8 more or less candy materiaL AUIuMigh the gravel is largeijr qnartzoee, pebbles of otlit r iiiat<"rial arc also plontifnl. Tlic size of tlic ranges from a fraction of an inch upward to cohbleBtones C or 8 inches in diameter, bnt the average size does not by for reach these dimensions. On the bed rock larger, partly rounded frapnciits mx-ur o<-casionaIly. In the channels with {jraiiitlc bed nx k well rounded bowlders several feot, hirge are .soiuetiiueM found in the bottom. In many of the tributary channels, saoh as the Harmony and the channel at the northwest end of Cement Hill, the pravel on the bed nuk is jtartly aiifruhir and fbctly washed. In the Uaruiuny channel bodies and sircak.s of bluish day alternate with streaks of gravel near the bed rock (lig. p. In the upper part ot tiie ;,'ravel the pebbles aie generally extremely well ronnded iwlished, and bla< k, siliceous rocks make up a large portion of them. The dcc|)c.st gravel ha generally a dark-gray or bluinh color, and contains mncb iqrrite or matcasite, sometimes anriferons; streaks of reddish gravd also occur in the deeper iarfs of the mass. Nearer the surftoe the gravel is generally of reddish color. Fluviatile stratification is of extremely common ooenrrenoe. Very little gravel conn in the Banner Hill area, though the lower partH of largely eroded Noocene streams doubtless contained iiiueh of it. Ver> little gravel is found in the Gra&s Valley area also, and in the southern start of the Nevada Oity area. The largest acennralations ara found north of Nevada City, in the dee|)est parts of the ancient stream system, where they re:u;h a maximum thickness of 175 feet at the .Manzanita hydrauUo cut ( flg. 4, p. 98). The banks of Oement Hill sbovr 60 fioet of wen-washed gravel, with excellent tluviatile stractttn. Fig. 5 (p. 99) shows nomconformity ohservetl in the bluff.

Diyiiized by

98 GOLD-gUAUTZ VEUib OF NEVADA CITV AND GRASS VALLEY.

esteem.

Rhyoutic Tupf8.

tlie HuriferunR gravels He, in the (leejier parts of di preaioiiai a aeries of Ugbt-eolored or white clayey or sandy rocks, more

or )es couHuIidated, and ooBBiiMnilydeaeribed as pipeclay aud siiixl. These are largely tuUs, more or less pure. Gertaia of the beds oousist nearly exelntfivefy of minute fhtgineiita of glasH, while others are ho admixed with mainly grauitie detritus m to nearly ma.sl£ their tuffaceous character. The fragments, (if glass and of {.Miiiiif ic iniuerals, are generally very sharp and Mgalar. Beaidea, bodies of gravel are also ineludel in tlietiiflTaceous series, and, on the whole, it ia impossible to draw a distinct line between the aariferons gravels and the rhyolitic tuffs. On the Houtliern face uf Cemeat Hill the line between the two fonnntlona ia fiiirly sharp, separating CO feet of gravel ft-om over 'im feet of rhyolitic toll A little rhyolitic material is found in the sands of the main cbmnela down to a distance of feet, or even less, from the bed rock. 'I'lie occurrenee of the rhjrolitic tnfF Is practieall y <'niifiii('d to tlie northern ])art of theJBsuuer iiili and Nevada City tiaeta.

The composition of several tuffs and Handstone8 is shown liy (lie ontheuextpagejthe partial analyses were made by Dr. H. K. Stokea.

It is apparetit that the purest tufl* has very nearly the comiiosition of a rhyolite. Grains and flake of a brownish translucent mineral, with

faint double refraction, are aban* dautly especially in the roeka poor in alkalis. This ia nndonhtedly the same kaolin mineral reoognized by Mr. H. W, Turner in his lone sandstone.'

mw/'///Mm

, 4._s.>( tinn of HiiiierJiu-rDt fonartlt— M 51 iiux-iuitA uikiir, Noviifln City.

VMflMlb Add. Itqtt. U. S. UmL Snrrajr. fMt II, UM. p.4M.

Diyiiized by

ty.c.

Tv.O.

Mv.C.

O-.&#x27;. 70

co

KiO

1.M

l.fB

.U

.Ss

S.41

9Lss

n.u

]M.ai (Mia miiM. S ftetatoroM hm*. flairfy day cMUtolng no rbyolii frucnmii. bsmB bad rack.

]r.ailMllMWMtrWMSMVMylMllM. FmifejaUtotna: ]H.CtlfMMallftylt,NlM*kmMndu WMtoiwiirt— *fawityMftiM— UW.C.i OmbltaiK villi* Mo4staMi fcwihrallto ftagawBte.

At the C'eiiieDt Uill diggiugs, in the northwest corner of the Nevada City area, sandstonee and gravel oeenr oemented by alnosfe pue . yeltowiah opaL

Anob8Itic Tuffs.

It lias already Iwcn inentioiK"*! that the hiph, gently sloping ridges of these districts are coven*d by audesitic tlows, and their general char* after as tnlEB and tofllMseoiw lyreodaa baa alao been deaeribed. Aa

FM. I.— BlDirrt bytaalfa mk, awr city iwm mli, Vavaia City.

nile, these tluws consist uf a detritui mass wcli cemented and made up of aadccntio grains. Abnndaot angular or rooglily rounded fragmenta of (if 111! sizes up to a foot or more in diameter arc incIo,sed in this finer grained mass. Tliis andesite ia of a gray to brown or reddish color, hardly ever greenish, and is oaoally dtafelnctly iwrphyritic, with Buiall crystals of white feldspar and VhiA angite or hornblende. As a rule, it ban a nmgh, tnushytic ampeonmoe. Mica ia rarely found.

100 Qold-Quabtz Veins Of Nevada City And Gsass Valusy.

Pyroxeiio fhotli aufjite and liypcrstlicnc) is almont invariably present. Black bujjaltiu LuiubleuUe occurs wilU the pyruxeue, aud nnialljr fn larger crystob. The gronndmaw to partly glassy, or of ft very line grained, boiomystaUine stmotnra. The tUckue-sa of the vol*

canic flows ranges

the Banner Hill

district to about 200 feet in the Nevada Gity dietriet The easily disintegrating oement renders (be exposures unsatisfactory, and a deep, reddtoh soQ nsuRlly covers tiie tops of the ridges. This disiutegratim, and the ten* deneyof the de* composed material and reHidual andesitie bowlders to slide, dinviiliill. ot'ten make tlie roiitacts witb tlie iiiidcrlyin'j formations aud diOicult to trace. Good are found lu the vicinity of the rainy gravel mines. The best expomre, though praosoo

Scale.

isooftrr.

no. 7.— Vartk*! Metkn along Wcat Hannany inoUiM, abowiag depth of fomutxms and modaaf

tically Inaccessible, IhIu the blnirof the Manxanlta hydranllc pit north

of Nevada City. imconrorinabl y on tlic sloping; sm fafe of tlie white elays and Kand, there are here at least four tseiKirate tlows of andesitie tuff, each 30 to 90 feet thick and separated by irregnlar,

Alluvium.&#x27;

surfaces. The anion ut of angular aDdesitic t'fjfrM is not constant, and some rows consist ontiioly of till' fiiio, (It'fritiil. 't'i.nnf itifj tiifV. Of snch character are the tuliti overlyiug the clays and giaiVulkjuxiKAsed in the hydraulic

s.E. .-l.W

Scale.

'no

Alluvium.

The alluvial art" if small extent, and consist principally of a few Sravel data along Deer Oreek,

Little Deer Creek, and Wult i ctk. Many of these bodice of gravel an fornu'd of dt In is from hydniuliiavol niiiics.

Alluvial sands and c-layn have iM-cuiuulateil in several swauipy tiata to the soatli and aontheaat of Nevada City, and also to some extent near the race tra<-k. Tin; largest alluvial lie in Creek below the providence uiiue, and consist of well-washed gravel of qnartz and metamorpbic rodEa, with some sand. They are made np largely of the debris from the extensive hydraulic mines just north uf Nevada

City, which had

Sano.

their principal outlet through the first gulch emptying into Woods Bavine from the cast* III the Grass Valley district extensive flats of sand and clay occur on both branches of Wolf Creek aliovc the city, and Huialler

grav<>l flats are found at intervals along the creek below thedty. In the southwestern part of the tlicic at the headwaters of the gulches a nnndwr of shallow alluvial flats uf sand aud day, u.sually uf a marshy character. The largest is found south of the North Star mine.

FN. 9.— SMrtIra ta irarfcteii* Odhi drHI

Diyiiized by Go9gle

GEOLiOOlCAIi UIHTOIIY.

rsum6 of history of the bed-rock series.

Witli tho kiiowUMlfje a<'(min il by tin-more detailed 8tnd7| the history of the bed-rock stries nmy now be briefly reviewed.

Th ndimentaiy Mtiee of th Calaveras formatioB are, without niucli doubt, tlie oldest ro<-ks in the district. Tlipv coiniMiso scvpnil subgroups of differeut character, and these may well be of consider ably differin g age. All tbat can be said deflnitoly is that they antedate the Mariposa formation, and it ia probable that tlicy all are Paleosoie. No volcanic tiifls arc foil ml in tliese beds, thou;;li Paleozoic eruptives are known in this turniation from other parUsof the Sierra Nevada.

The fonnation was folded and stray eompreMed long befiwe the igneous rorks now assm iated with it had made their iii iK it atict'. In theforwatiou there is absolutely no evidence of syncliues ur anticlines, the compression having evidently reduced theaeriea to practically parallel, extremely sharp folds, upon which a schistosity has g( normally been KuperimpoRcd. in most oases apjiarcntly coim iding with tiie lieildiiig. Subsequent intrusions have broken up this once-connected formation, and ftagmeots of it are now contained in the Inter igneoaa rucks. The scliistitsity in the Calaveras formation of Nevada City and Grass Valley docs not, then, necessarily correspond the lines of disturbance in tlie bed-rock series devdoped snbseqnent to the granitic tntmaion.

Tlien, after a considerable interval, in-ohalds followed the iutmsions of the diorite-gabbro pyroxenite group. The relations of this group to the other rocks is one of the doubtful pointN. On one hand, there eema to be an intimate relation between the gnnodiorite and the above nientioned group, iinlicafed by the occnrrenee of what may be transitiouH, and it is well known that the gniuodiorite may, to the contact, pass into mora basic allied rocks. Furtlieff dike-like masses of and gabbro occur in the diabase and poriihyrite, and even in the Mariposa formation (short distance aliove the Washington mine, upjier Wolf Creek). On the other hand, there is clear evidence, ftom certain well-ex])osed places along the grauodiorite* diorite contact, that the former is an iiitrnsifin into the latter, ami tln'i e is excellent evidence allorded by dikes tiiat tlie diabase and porphyrite an later than the diorite-gabbro group. On the whole, the probability is that the diorite gabbro group of this di.strict is older than both the granodiorite and the dialNwe and porphyrite. It is of the

lanmii.] HI8TOKY OF THE BED-BOCK SERIES. 103

game areas the dioritcs of the ftMdliillsof Nevada romity ludian Springs northward, iu wliich also dikes of diabase aud nnied porphyritM ocear.

No very fuitisfoctory evidence has obtained as to tlie aeqnoiice witliiii the diorite gabbro group, bat as fur us it goes it seems to indicate that the baHic rot-ks were the older and the more neid dtorites the later pats of the iiitnisiuit. It is indeed not that various parts of th' jiabbro and serpentine may be of iliflereut sme, for it is well known that dikes of thest* rocks in otlu i parts of the Siurra cut the Mariposa formation. In the teztof tlie folio of the special sheets' it has been stated that jtrobably none of the iffneous rocks are oUler than the Marijwsa turuiutiun. It is, however, neoessiiry to admit that tbisis m very donbtAil point In the case of thediOTite-gabbro group. If the dikes of tlinbasp and porphy rites oei-nrrin*; in it are eontcmporane* ous with those similar rwks avccoiupunyiug the Mariposa formation, it is oertMin that the rocks of the diorite-gabbro group at this vidnilgr were intended before the MariiKtsn slates were deposited.

After this the eruptions and ititrusious of diabase and allied porphyrites took place. This was not a local phenomenon, bnt similar igneons ;ietion wenrrcd all along the foothills of the Sierra Nevada, resulting iu tlte building up of volcanoes along the shore line to a height of many thooMind feet above the present surface, only the interiorparts and roots of which are now visible. During the earlier part of this wUlespread igneous action the late Jurassic Mariiiosa beds were laid down, and the tuflTaceous rocks of this uge contain abundant nient.H of porphyritic rocks of an effusive type. The nmterials extruded dnrinj; this perioti of intense volcanic action include, as is to be expected in u series of large volcanoes, rocks of both intrusive and effusive types. Basic rocks prevail, ranging in composition ftom medlnm'gralned diabase to angite and hornblende iorphyrites with eryptocrystalline groundmoss; iu the latter it is (|uite possible that some ghtss was once present, which is now devitHAed; aa eztensiTe devltrifleation can certainly not be re<*ogni/c il. HiK-ks of nioderate acidity ocenr to sniall extent in this igneous series, aud are youuger thau the basic predominating nick, while very acid rocks or alkaline roeka are absent. Many of the effusive rocks eorresjxind closely in miueralogical and chemioal to the modern aiidesites.

A fter the deposition of the Mariposa beds and the close of the accompanying igneous activity, followed the ini|>ortant post Marl po.saorogenic disturbance. The Mariiiosa beds aud tuffs were folded, compressed, and wehled with the already compressed Calaveras formation. The igneous rocks were over large areas crushed and rendereil schistose by iiiteuse dynamo-chemical metaniorphism, while other areas escaped the pressnre, which was chiefly concentrated along certain lines and belts of shearing. Within this riod falls the formation of the Indian Flat and the Brunswiek amphibolite belts.

wmmab.ctL.vm.

Diyilizua by GoOgle

104 Oold-Quartz V£In8 Of Nevada City And Or48&amp; Valley.

Now follow'dthe last and fartliost reaching phase of iVqioous nativity, ill the form uf the iiitrasiou of cnoriuoas masses or bathohtes uf grano* diorite In the range, tearing aaniider tlie older rocks and bending and tvristiii;; the oMit srliist masseti.

The intrasiou must liave taken phu:e under great depth of i-rlyiug but now eroded nick. Plainly shown as the fact is by gcWogical iDveatigationt the actual mechanical iiraceM almost RnriiaaseM our i*conception. In Rjnte of tlio jrn'.it ih:\f nmst have ht-fii cxcrttMl by the intnuliug uiasts granixUoriie, it is not apparent that this pressure has prodoced any mhfatose stmotnre on the surrounding

rocks; th' usually iiiitcdati s tin- {jranitiiintmsion, thOOgh in some cases it has been producvtl subiiequenl to it.

In this oonnection one fhct dewrves to be emphasised: There is abao* lately no evidence of fusion of the masses accompanying these gigantic intrusions molten ma{;nni: it shouhl expected in tlie Sierra Nevada if uuywhen but except very locally it is not found. This, ns well as matiy other facts, throws great doubt npon the theory of <rt'n(*sis of ifncon.s rocks by tlu' fusion of scdinu'iif s, a theory not without its adherents at the present day. Suialier masses of basic material are fireqnently found along the contact of the granodlorile, showing evidence of earlier consobdation. Contact affected many of the surrounding rocks to a width of up to a thousand feet; still larger contact-metaniorpbic are fonml adjoining the large grtinite areas of the higher Sierra.

The dynamo nietnmorphic action after the intrusion of the but with less intensity, uud evidences of this itlc distnrbanee are not noted in the special areas. Intmsions of small amounts of very acid, alkaline, and also of more basic nnifrnias (uplitos. and lamprophyric dike rocks), the until iutmsinn of granodiortte and may be regarded as forms of difliBrentiatloii of that marina.

The last piiase of the history of rlic Itcd-rock series is the formation by compressive stresses of an exl iisive tries of joint systems uud llasore systems of diffiMring directions, generally not coinciding with

tlie nf (lyiiaiiiii- (lisriirl>,iiic(>. AIoml.' these joints and tissnres ascending thermal waters depositetl the ores and altered the country rock. Thus the hydrothermat metaowrphism was the latest alteration to which the rocks have been rabjected. S<-rii s ot joints or sheeting parallel to the quartz veins are illnstratod lu I'l. Ill, opposite, and lig. 10 (p. 183).

The close of the granodioritic intrusion Mis between the end of the

and thf Chico Cretacetms. prolialily in the be'inning'.' of the Cretaceous period. At that time the Sierra Nevada must have formed a mountain range of imposing extent and elevation, in wUeh tha tocka now exposed at the surfiice were deeply buried.

Geological History.

History Op The Superjacent Series.

After the time ut° t;rauitic iutnisiuus aud Ibriuatiou of quartz veins Ibllowed a period, inctndtng the latter irt of the Cretoeeons and the iMinningof tlie Tertiary, IWim irliirh no {eulojrieal reoordn are preserved, at least iint iti tliis vicinity. Hut there are iiidieafi<>iiselscwlire that the range during the whole time was a land area, and tliut tiie moimtains of the early Oretaoeoua were aubjeeted to long degradation dnrittt; wliicli they were reilin ed at least to a eonditioii of otily moderate relief. Probably at the close of the Cretaceous the lirt break along the eastern margin took place, hy which the Sierra Nevada was differentiated flwm the Interior plateau and began to attain its present characteristic form. Krosion, wore down broad valleys in the old plateau, and at xonie time during the beginning the Neocene period the relative relief was snch as the cast of the lavas covering it has largely preserved for oar investigation to-day.

Tbb Hbocbmb Bsd-Book Subpacib.

The Sierra Nevada was, in this latitude, a range of moderate height

and relief, with a chain of prominent fbothilla, nnnle ii]) of tlie .Inrassic, lavas, with middle slopes cbaracterlxed by broad river valleys aud moderate relief, made np of the Calaveras slates, and with higher and more rugged summits made npof granitic nx kH. Traces of the old Cretaceous ]>lateaaorthe pre-Neocene peneplain are visible at intervals in the relief.

Excellent opportunities are offered in this dlstriet to study more

closely till-old ViiM iMM' siiifaee. The areas <o\(t<'(1 1y the Neoietie deposits are numerous. The elevations along the couUict lines aud the data available (Vom the nndergronnd exploration of the anrifenma ohaanete afford snfUeieut materials from which to construct a contour map of the Neocene surface f I'l. 1 1 There are, of course, many spaces which must be tilled in by suggestions obtained from tuijacent and many details may lie inomrrect, bnt it is very certain that the plate

gives a generally correct conception nf tlie topography. course, the map is atl'ei-ted by any .sub-seijueut or tilting that the old snrlaoe may have nndwgone. Parte of the area where the data are insutticient have been left blank. The general features of the contour map show a prominent relief, but much less cut and s<'ored by creeks aud ravines than the modern Banner Tlill, the Town Tallc Ridge, and O.borne Hill were then, as now, salient ]MiiMts of the y. These etiiinences rose from several hundred to over a thtiusand feet above the depressions, lianner Hill waa, however, an nnosoally prominent point in thia part of the compnr* atlvely gentle middle slopes of the Neocene Sierra, its hard silioeoat

Diyiiizea by

106 Gold-Quartz Veins Of Nevada City And Grass Valley.

brmias stroiiply resisting disintef,'ration. Xorth of Banner Hill a proiuiiieut, liigb ridge of siliceous at gillite divided the watersliuil of the Kvadft basin from the main Taba River, flowing from Scotts Flat norlliwani toward ISlue Tent aud North Columbia.

West ofTowu Talk the drainage was dearly westwartl, down toward Rough and Ready. The Grass Valley tract ia its northern part waa drained by the Altachannel,headtngnortheastof Osborne Hill. There is no evidence that tlie cluuiiit'I cniitiniuMl casfwanl to Bneiia Vista slide, as stated lu a previous publication.' Gooil proof of this is furnished by the fact that the rhyolitie tulT from the main Yoba channel also tlie Bneiia Viala diaiinel and tlie di pression southwest of the Washington mine, but did not overdow into the basin of the Alta channel.

in the Nevada City district it is clear that the main depression was in the vicinity of Nevada City, for there the acciuiinlatioiis of jrravel, sand, aud clay are deepest and the elevations of the bed ruck lowest, tip toward the highlands of Town Talk and Banner Hill the depth of the material metitioiieil arrows less, and at ertaiii elevation the aiidesitic tufl' retA directly on the bed rock. In the lower part of the basin the enriouii feature is preaeuted of an almost continuous channel 4 miles long and ])r;i( i ii ally levol.

rroni Pi ( ks at the head of Native American Ravine, at the northwest corner of the Nevada City tract, whero the elevation of lowest bed rock 8,680 or 8,000 fiset, there to without douM a eoiitinn* OUS channel to the Empire shaft, with a lowest rwk elevation of 2,060 feet. Again, there is no reasonable doubt that the channel is oontinnons to the great hydraulte pits northwest of yevada City, and here again the bed-rock elevation is 2,<m0 feet, even Kinking to 2,625 feet in the vicinity of the old Merrifield mine. From here the lowest channel continues eastward over the bed rock of the hydraulic gronml, at elevation ranging firom 2,630 to 3,010 fbet. Again, at the Bouthcni end (if tlie Manzanitai liaiuiel theelevatioii is '2,Mi> feet. From the Mauinita pit the rich gravel uu the bed rock, a few feet thick, has been drifted on up to the Odin mine, at which place the lowest bed rock i8 2,C5.'> feet. From the Odin iik Iiihthe channel h.is extensively proM|>ected in the belief that it <-onnectel with the Harmony channel under the lava hill. The channel is here wider and the gnivel of lower grade than farther south. At the Howe cut, where the channel enicrpes from tinder the rid}:e, the lowest bed rock has an elevation of 2,<JU feet, though at the inner partof thccuta harder, granitic bedrock ledge rises to an elevation of 2,070 ihet. 8nch local iueqnaiities are often met with in the ohl channels. There is thus no decided evidence to be derivcl from the grades as to the direction of the old channel.

Bull. Ural. Suf. Am , Vol IV. I8B. The cbanot'l at VlaU proUably graded towanl tka aMt, tottw BBlD Tate lOnr.

U9iwMai.1 HIBTOBY OF THE 8UPERJACBMT SERIES.

Other fiMSia sUow, however, thitt the Cemeut Hill channel, iu the firt place. iniit have Howwl from the northwest to the southcuMt. First among their i8 the evidence from the gmvel. At Pecks diggings there Uonly tw fiMt of imperfectly washed quarta gnvel overlain bj the pliiys aiirl snndstoiifs of iliyolitic series, which here attain a depth of only 70 feet. At the diggin8 northwest of Nevada City the gravel is 60 feet deep extremely well washed, and covered by from lAO to 200 feet of lightlored rhyolitii; beds. This alone shows plainly enough that the direction of the channel was southeasterly. Regarding the other part of the channel, it has generally been supposed that it came down {vom the north, and that, bending aboat near Nevada City, its BOW eroded lower eoiirse followed the present valley of Deer Ci'eek westward toward Kough niid Keady. At the first glance this not only eema plausible bnt actnally snstirined by the inwle of the channels, bot there are very cogent arguments aMinst such a In the first pteoOi as in this vicinity the of erosion between the rhyolitic bts and the andesite is Insignificant, it shonid confidently be expected that some of the rhyohtie material would be found in the neighborliood of House and IJougli and Heady, soiitli west of Nevada 'ity, where fragments of channels are iireserved. Nu such beds are, however, fbnnd there, the andeaitie tnff resting direeUy on the bed rock or the gravel. On the other hand, iHfstniiing that the Matizanita ehannel did come from the north, we are confronted wiih the fact that the outlet of the Harmony ohannel at Laney's tnnnel is somewhat lower than the bed ro<-k at Howe cut, so that, on this sup|)osition, in no way— the outlet being to the eastward of llowecut — could any ennnei tion then have existed between these tW4) channels. That the Uarmuuy channel is continued toward the northwest to Join the old Ynba River is clearly shown by the lower deposits at Koinid Mountain lunl tlic still lower fragntent of cliaunel preserved at Montezuma ilill. There would thns be no room left for headwaters of sneh a large channel as the Man- 7:anita, on the supposition that it came from the north. Furthermore, the .ManzanttAi channel was extremely rich in coast gold. To the north of it are no quartz veins worth Ukentioning, while immediately to the oatli of it are the rich vein systems of Nevaila City. On tlie west, toward the Providence mine, begin a series of ninch Imrder ro<"ks, resistant to weatiieriiig, and whicli would easily tbrm a barrier, just us the slate and diabase of Banner Hill, Feileral Loan, and Tbwn Talk still form barriers to the east and south.

The Manzanita chaunel then formed the central drainage of a tlat depression in the easily eroded surrounded on east, south, and west by an amphitheater of rising hills. This drainage is indeed the most natural one to be exje<'ted in a vit-inity where f he tendency to transverse drainage is not so strongly develoiied as on the tilted plain of the modern Sierra Ievada. It baa been ahown in a former paper*

'BuaOMLSiM. Am., VLIV,|hM.

Diyiiized by

108 aOLI>-<)UABTZ V£IMS OF NEVADA CITY AND QBASS VALLEY.

tliat tlic j;i:iih's of tlifi Nem'eiu' river i-oiirses cleurly iiMlicate tliiit such a tilting ha-s taken place along an axis iiarallel to the orest of the Sierraa, and that the amoont of it, tbongb not exactly regular over tbe wboto slope, WU.H 00 or TO feet pr niilo as a niaximuin. Applying tbis piincipie to the Neocene ilminage eystom of Nevada City, the diflBculties ars overcome, and the drainage becomes a very natural one.

Tbe Cement Uill channel, with a direction from northwest to south* ea.st, had tlien, iH'forc tin* (iltinfr. :i of fiO to 70 feet to the mile. Tbe partly eroded channel between thewesti-ru end of the big hydraulic pits and the Manzanita pit, which now has a slight grade of 20 feet westward, had Itefore the tilting a moderate grade of about 50 feet per mile eastward. The channel between the Manzanita and the Howe cat, now practically level (excepting the hard projecting ledge at tbe latter cut), and which runs nearly due north, had before the tilting a sli;4lit iioirh ward nf nbont feet per mile.

From tlie iiouecnt i.eievatiuii 2,(i.iO) to the lowest bed rocii at liouud Mountain, miles dne north, or 1 mile east of the line of tilting (elevation L>,lt'J.~>). tlicre is a present grade of 10 ftet per mile, which before the tilting was 3U feet mile.

From lionnil Mountain to the lowest bed rock at Montezuma Hill ('2,3rrii {fx't elevation, acconliug to I'ettee in Whitney's Auriferous Ciravels), a dislanee of iiiih's in a nearly due we.st. Ili<>re is now a grade of lUO feet per mile, which before tbe tilting would iiave been 30 feet {ler mile.

From .Moiilezuma Hill down to Frencli ("(irr:il, along Shady Treek and tbe present Vuba Uiver, tbe ouly way which tbe Manzanita iiiver oonld have followed, is a distance of 6 miles, with a present grade of 100 to the mile.

Till' I larniony channel must havejinwl the Man/manila a mile or two north of the lowe cut. The Harmony, coming down in a wejjterly direction, bas now a very steep grade ot about lAO feet per mile from the Kast Harmony to Lancy's tnnnel. Ht'fure tlic tilting it hail a ;;rade of about SO feet per mile. Ksist of the Emt llaruiouy the grade increases rapidly as tbe high ridge nf siliceous argillite is approached. It lias IxMMi held by many that tlir Harmony channel continues an indefinite distance np the ridge. Thii is imimsaible, ii.s only a few miles eastward the deep Yuba channel, from South Flat to Blue Teut, crosses the ridge. The Harmony channel is well np toward head* water s. and nndrr flie Harmony rid<;(' <livid<'s np into several hrnnclics. The .subangular character of its gravel and tbe 8teep graiie:* prove that the divide is not for distant. Its richness is not because of its being a main and important channel, bnt la-canse of its erossiii); a $)ystem of rich quartz veins. It is barely iMissible that a deep gorge <-ut.s through tbe ridge of siliceous rock and extends as far east as the Fountain Head, bat it must be ehanicterixed as highly improbable. The vicinity

>9m aolacic AtlaaaT tke Vailed Slatw. FMio Xo. M, SMrtarttlo, OL

HISTOKY OF THK SLTEK.f ACKNT .SERIKS.

of tlie Fiuntain Head probably drained toward tlio main Ynba Tfiver eastward. There is, of course, no reason wliy auriferous cbauuels aboard not 1m ftmnd on the east as well m on the weat side of the divib There is also a differenc e in elevation between tho Hurfaces of ttie rhyolitic flows of from 2U0 to UtO feet between tbu vicinity of Cold Spri u g and Fountain Head. Snch great difference wonld scarcely exist if there bad been aoonimnnicatioQ between tbe two bK-allies.

Consideriiip: tlie snbse(|ueiit tilting, the Neocene rock surface would origiuaiiy have had a less shar]) westward than is indicated on the map. Banner Hill, instead of rising to a height of 1,200 feet above tlH> Man/.anita cbaimel. as now, WOUld have had S height of only l,UoU I'eet above that iioint.

TIIK ArRIFEBOlTS OKAVKLS.

TTavintj tliu's examined tlie smfaee on .lliell tlie Neocene deposits rested, it remains to outline brietiy the events that caused its burial under Neoeene sedimentary and igneous depoRits. At a period immediately jireceding the volcanic emjitinns of rliyolite and andcsite the, aecuniulatiuus of gravel were not deep at any part of this area, located well up on tbe ridges dividing the main drainage lines. Along tliese main rivers, and principally ahmn the great longitudinal Valley of the Ynba from You lU't up to Not tli Columbia, masses of pravel several hundred feet in depth had accumulated. One (though not the only) of the principal canses of this exceptionally heavy gravel mass is to be fimnd in the fart that tlie Ynba Tliver, flowing on tlie middle slojies in a Innoad and oimi valley, had to turn and force its way through the IbotUll range of Juraimie lavaa in a relatively deep and narrow canyon, almost as deep as tliat of to-day and well shown by the present relations at Smartsville. This foothill range acted as a barrier, restraining the gravel niass<>s in the open valleys of the middle sIoik's. In the Kevada City area the prevolcanio gravels reached the greatest depths along the Man/anita channel, and it is donbtful whether they have at any place exceeded a thickness of 40 feet. lihyiditic fragments are found at that elevation above the bed rock, and even lower. It is donbtftll whether the gravels, 6U feet thi<'k, of the hydraulic pits northwest of the city are antevolcanic; the gravel is different that generally found in the parte of the Neocene channels, and baa more the appearance of tlie extremely well-washed black gravel" wlii<'h appears at the higher elevation and which belongs in the rhyolitic period. Dutside of the main drainage channel there was only a fttw feet of gravel on the bed rock along the streams, and in by fWr the gii iti ' number of the andeaite or rhyolitc rests directly on the L-ed rock. There is no reason to believe that the autevolcanie gravel in this vicinity antedates tbe Neocene period.

Diyilizoa by CjOOqIc

110 GOLDUIBTZ TBim OF ITBTADA CITT AMD OBAW TALLIT.

Thk Volcanic Flows.

Sach were the conditions wben eruptions of enormous masses of rbyolitio tuffs began on tbe headwaters of the Neooese Tuba Bivtr. Their general cbaraeter bas referred to above. It is probable that they wore erupted as iiind flows, einerf,'iiit,' from the crater niiiipled with much water, and that there was not only oue but a long series of flows, in tbe Intervals between wbieb tbe older flows were to some extent worked over ly tbe runniiif; water and iiiterstratified with Iay, sand, and gravels of local origin. These rbyolitic tlows, 200 to 300 ftet tbiek, are well exposed at Alta, on tbe Oentral Padfle Kaflroed, and at Chalk Bluff, near Vou Bet. At the latter an extensive Neocene flora was colloctoil by Mr. C. I). Voy and examined by I'mf. L. Lesquereux.' The rhyulitii: tiows of Nevada City are the exact stratigraphk) equivalent of tbe rbjrolite tnff of Ohalk Blnffli, and there eaa tlins be no doubt about tlieir ajre. Leaves similar to those of Chalk Bluffs occur at mauy places iu the vicinity of tbe Manzaiiita chauuel| and with some tmrnhle it may well be possible to obtain a good collection.

Tlie fiiIVs are well exposed at (\hiaker Ilill ami Scott,s Flat, farther duwu the Neocene river, and again uu ihe north Hide ot° the Washington ridge at Blae Tent, at which plaoe thc are several hnudied fiset thick, the top stratum an elevation of 3,00*1 feet. Near the place where the upper 2jorth llloomtield road crosses liock Creek, there was a low gap in tiie ridge between the main Tnba and the ISevada City basin; tliruugh this gap tlie rhyolitic tuffs poured Into tbe granitic ba.sin. It appears as if north of Blue Tout there was an obstacle, such a8 a narrowing valley, turciug the uiaiuies over the low divide in the adjaoent drainage. The first flows found their way down into tbe Ilarniony and lower Manzanitii channels, raisin.,' a ilaiimiinp of the latter, which again, of courMi, iirmluced accuuiulation ot'saud and gravels in the upper part about Nevada City, and to this damming it is believed the heavy gravels of the Manzanitsvcut and remont Hill are due. Subsetpient flows found their way down to Bound Mountain and Montezuma Hill, obstructing the channels to still greater extent. At last the whole of the lower part of tbe Kevada City basin became filled. The elevations of the top layers now ranfre from 3,100 feet on tlie eastern side of tbe basin to 2,740 feet at the northwestern corner of the Nevada City tract, a distance of ff miles flrom east to west. It will be noticed that on the of a tilting of 70 t'wt \n-v mile the surface would once, over this distance, have been approximately level, and about at tbe same level as the top strptnm of 43ie ibyolitie tuff at Bine Tent.

mart locality a matMr of mmm dooM. to mat nour mtemMUt, kavlng been covered IqrlqrdMuUc <lbrh. Profnuutr Whitney atotaa that tha aiatilx to a rbjroUUa tutr, but in the rir apecdnriM I exAmlDed. bv the vonrtcey of Prof. A. C. I.aweou. ct Berkeley, tiie rhyolltlo character to aol clearly appannt onder the microMope. At the morality I was told that the learea were fouS Jnal below tbe while tnlT and at Ihe top of the oxteaeive beach grarela of Tov ISet, aarant tas* triad tat abava tka bottoai af tka daafaal akaaMl.

Diyilizua by GoOgle

History Op Thb 8Upeujacent Series.

The rUyolitic butts flit! reach the southern and hijrhost imrt df the KeViula City basin, nur did overtluw into the Tuwn Talk or Gru8ii Valley cliannd. To tbe cast of the Neocene divide, rising along tbe eastern tnarfjiii of the Gnis Valli v trai t, the rhyolitic flows again aiipar, liaviug reached there from the vicinity of Yon Bet. The divide was, boirovifff joHt bigh enongb to prevent tbis overflowing into the Alta ebannel.

As may be seen hy traciup the eontacts of atitlesite mnl rliyolite, tlie tturfitce was not even, liut Nubjucted to .some eriHiing action lu the interval between tbe two eniptions; bat it was not extensive enough to

produce any marked chaiifxe. In tact, tliosc iiitervolcanic chaiinelaf eottiug fur down into the rhyolite,and even into the underlying bed rock, whieb are so ebaraeteristic of tbe vicinity of Forest Hill, Placerville, and Mokelurane IIIII in tbe drainage of the Aniericau aud Mokelumiie rivers, are prat-tically alwent on the main Yuba, although ou the headwater.s of the North Yuba, near Forest City, they appear again. Tbis Ik evidently caused by a difl'eriug time interval between the two eruplioiis; in tliis vicinity the tirst audesitlc th)\v fnun the Lola and Castle I'eak volcanoes tolloweil closely after the lat eruption of rbyolitic tnff.

During the latter part of the rhyolitic period many divides were flooded ond the drainage was partly changed. Tbe great Keocene orogen ii: movement of the Sierra probably took place between tberbyolitle and the ande.sitic eruptions, as i.s evidenced by the intensely eroding cliarai ter of the cement cliannela or intervolcanic channels. A tilting took place, elevating the eatitern part of the range mot strongly and the western part bnt little. Flows of andeaite tnUb, emerging tnm tbe craters as a mud, down the flanks oftlie Sierra in rapid succossiou, obUtei-ating the old drainage and UotKling many of the divided. Banner Hill and Osborne Hill alone emerging from tbe desolate lava plateau iu tbis viduity. On this inclined lava plain I lie rivers had to select new eoursws. in general differing consiilerably from the ones. The ])re.sent draiuage was developed, charavtcri/.ed more than tbe Neocene by a transverse dlreotiou of tbe rivers.

Diyilizua by GoOgle

Chaptee Ix. The Orbs.

Obnbrax. Pbaturbs Op Thb Gold-Quartz Vbin8.

Although noUl IS very widely dittritmted over the Sierra Nevadft in veins ami jilacer mines, there is no other part of it which sliows such a concentration of vaiimble deiKisits within h narrowly ctin umcribed ana asooeara in the districts here discoBscd. Almost the only form which the primary dejvositH of the bed rock series jtrcscnt in this locality in that of (|uanz veinM,con8i8tiug of tissureii of somewhat difllinDt tluNiirh closely related character, filled mora or less eontlnnoasly byqaarts earryin native (rold and anrifentuH metallic imlphides. These Assures, belonging to several systems, are usn ally traceable on the sarfkoe by means of the often harder, projecting quartz croppings, and attain a maximum length of a few miles; by far the most, however* can be traced only a few hundred or a thousand feet. In some localities the extremely decomposeil surface rock aud the narrow charu<-ter of the Teins render the tracing of the onterop a most difllcnlt tindertaking, in which the miner's pan is an indispensable adjunct, for all quartz in these districts contains gold, though it may present in very small qnantitiee.

There is in some quarters a widespread belief that the veins of Nevada City and (Irass A'allcv are in some way connected w ith the lonp, continuous linked veins of the Mother lode. This is a mistake, for the last branches of that vein system are found about 20 mfles aoatli of

Grass V;ilh'v. and, moreover, the veins of (irass VaHey and Nevada City hitler considerably in their general character from the veins of the Mother lode.

With some notable cxc eptioiiM tbey ara narrow and produce a comparatively liivh grade of ore. They contain, as a rule, a much larger per cent of gold than of silver (by weight); the fret? gold is the most important constituent in tlie de()t h as well as on the surface, but besides there is a variable amount of ioh] and silver ni the snlpliurets.' The Strike varies to all jioiuts of tlie compass; the dip is usually Hat aud also equally variable in direetioii. With all these different direetiona It is, however, easy to distinguish two main systems, north-south and

' r 1 J ii M III M iti VI ly u-<*'l 111 t li'- 111 : ii:n rcii ill Im* lit fu iHliiplol t!i ri t tn ilrMi'iiiltr Jill tbi iiictiillK niiiirrul* uo'iirriiig tlio goM vt ino riii*|)UiiK llm nalive yultl, itiiu iuclutliuK (lit* aimple uiiil aalpliMMMil MMflidM M well M tallMMM.

m

Diyilizua by GoOgle

luiMUir.) OBNERAL PEATUBS8 OF THE VEINS. 118

east-weat veins. In the former syatem tbe veins may dip either east or west; io the latter, north or sontb.

The iiiitH'H of the (lras> \';i!!t'\ disri ict liave aiifl ♦'six'i'ially priHluctive; iwxt in proUuclioii I'uIIowh tbe Nevudu City district, and tlH Banner lltll district comeH third. A large proportion of the prodiution has been lerivMl tVoiii a few proiniuent V8, 80ch M the Eureka Idalio, liocky Bar, Nortli Stiir, Empire, and

A type of veiiDt different from the ordinary gold-qnartz vciiih, though nut of innch practical imiMirtaiice, oeciirs inOnW; Vulley, and is characterized by pyrrhof itc and iii a sraTifxiicof calcite, inartz, and feldspar. (See Crown Point miue, detailed Uecriptiuu, Chapter XVL)

Other Obpob1T8.

Though the fpiaitz veins in their (lid'erenf forms constitute the ovilj primary gold deitosits of the distrietH under uousideratiou, there are In yevada Ooanty a few aomewhat differing types of deposits of which brief mention may be made. The Pine Ilill gold deposit,' about lU miles south of Cras Valley, is charm-teri/ed by a zone of intense thermal decomposition resulting in the formation of kaolin, a mineral practically unknown fhim Nevada City and Grass Valley, as well as masses of secoiulaiy <|uartz resiiltinp from the of the jMrpbyrite in the vicinity. There are abundant veint) of barite, also unknown from tbe mentioned districts, and a little pjrite. The finely distributiHl gold contains raiuh silver. This de]>osit has doubtlcM been ibrmed by chemical action widely different from that characterizint; the normal veins.

Frimi Sweetlaiid. a town on the rid'e between the Middle and SrMitli Yuba, there extends down to the Yuba Kiver, northwest of Neviwia City, a narrow belt of line-grained, asiphibolitic slates 4altered to serieltic schists containing abnndant pyrite. This pyrite carries gold,

whicli is set free by surface decomposit ion ; the rock has been rnioed and milled at the Uotis miue near Sweetland. Tbe streak is well exposed on the Tuba River. This lu ucess again woaldi on the whole, seem to have been identic al with that by wbieh the normal veins have been formed, and the ililVerence is that, in the case of the Hoss schists, practically no quart/ iia.H been deposited, the penetrating tbe eehists, which were crushed to some extent, but witbont any notable spaces.

Another streak along which impregnation of auriferous iron pyrites has taken place extends in the add granodiorite and allied xoeks firom near French Corral the Yuba Kiver at the mouth of Owl Creek.* Here, too, tbe decompo.sed rock Iuih been rained and milled, though of very low grade. Tlie mineralogical character of this zone appears difltorent; there is no extreme thermal deoompositioii of the

Aw. Josr. Set.. Vol. X Lit . IMS, |i. K.

Cr. AUm of Um CalM SlalM, rUo Xo. U, aanrtoTtUo, Cl. 17 GBOL, PT 2 8

Diyilizua by GoOglc

It4 GOLD-QUARTZ TEIM8 OF NBVAOA CITT AND 0BA8B YALLBT.

rock, wMch is impregnsted with pyrite in gniius and nloog aeaim, and

there is no notalile (levelopnipiit of sfiicitt-. Iiiateiul, the pyrite appears to be couuected with epidote, which would show a doaer eonnecttoii of thia defMwit wilii Hia general metauHwidilBiii than with the vein depoaita in which epidote is onkoown.

Mineralogy Of The Veins.

Minkkaks.

Quartz. — The qnartz oc(!urring on the veins is generally massive, of a uiiUy white color and a lu8tr between glassy and fatty. A grayish, very aaay qoaitz ia eontidered an indication of poor me. Tbia iiiilk\ -white quartz is. as thin s<''tions sliow, usually made up of larpc. very irregular grams, occasionally with partly developed crystal laces. SometiBiea the crystal fiioes ahow more plainly, and this fliere are traDsitioos to the well-known interlocking comb structure. This, however, in its typical form, is not very common. In the Osborne Hill and Centennial mines a radial strnctnre of the massive quartz is sometimea noted. Fluid inclusions are abundant, though soiall, and naoally ineg* ulaily li-t! ihiitt'd. WtW (k-velopod crystals are not common, and are chietly tuuud in small cavities or vugs in the massive quartz. Certain veCna, imcb as the Granite Hill, are of very dmsy character, long, imper* fd'c t crystals coating the walls and radiating from fragments of the country rock. AH of the ore minerals. subsequently to be described oc<-nr as inclusions in the quartz.

Opal and chaU!edonite.—\n several mines small qnantitiea of a brown* ish clialccdonite. extremely fine grained in stnu-fnre, (M cnr with the quartz. Oiten it is of such deep-brown color as to be hardly translucent in thin section. It ia found aa irregvliur maaaea in the qoarti, or aaveinleta onttmg through it, or again, as at tlx' Oshorne Hill mine, fllllnff cavities and surrounding projecting quarts crystals. Gold directly embedded in the chalcedonite has tMsen found on the OOO-foot level in the Rush and Laton shoot, Empire mine, and 140 feet below the surface in the Hudson Hay shaft. Professor Blake reiMufs "grayish-blue or white opal, allied to cacholong," from the North Star minr,* while Proitesor Silliman mentions chalcedony from Maaaachusetts Hill, Kate Ilayt-s, and Knreka mines.'

ValciU. — Cakite occurs in small quantities on every veiu lu the district. In the decomposed oonntry rock adjoining the vein it is very abnndant, though always in massive granular form. In the quarts it ocoujs frequently as small |articles not easilj' visible to tlie naked eye; occasionally, also, as larger masses, of white >loi', breaking into goodsized cleavage piecea— for instance, in the Spanish mine and in the South Idaho. Otystallized ealdte ia occaaiottally ibnnd in cavities in

IflNEBALOOY OF THE VBDia.

Ike qoftrts; amftll aealmioliedroM (B3) wre noted ftom tb ProvidD6

mini'; larger, short, and thirk crystals, cninbiiiation of — and a stop calenohedrou, witb several subordinate faces, occur in the Empire mine, twantieili The calcite in the wall rock of the vein generally contains acne mm

and uiaprnt'siiiin.

Magnexitt occur.s nearly [lure, as u product of alteration of serpentine, in the Idaho and Maryland minee.

Si-riritf. — Tliis is a firm of muscovite, or white mica, extremely comulou as microscopic aggruites in the altered wall rock, bat the individual forte are hardly ever visible to the naked eye. The white color and greasy fed of many of the altered vail rocks ara dne to this mineral.

Maripoaite, — TbiK is a bright-grecu, foliated mineral closely allied to ntusoovite. The graen color is due to a small percentage of ehrominm. It occurs in sniall <iiiaiititi< s in ma-riiesite or quart/ in tlif Idalio- Maiyland mine. A little of it was also noted from the i'ruvideucc miuo. Generally it appears to he a pradnet of alteration of serpentine.' There apptan to be no good reason for sarating it from fiichsite or ehro' miferouH nmacovite.

SeheeliU. — This mineral, a tnugatate of calcium, in stated to haVQ occurred in considerable quantities in the foot wall of a mine on How> ard Uill, Grass Valley.' This is interesting, if authentic, being the only occurrence of tungsten in the district.

Xatirr ffdhl. — Metallic gold is contaiii(><I in all quartz veins of this region iu smaller or larger quantities. The most common form in which the gold appears is that of minute flakes and particles, as a mle not visible to the naked eye. To this there are, however, numerous exceptions. In several mines a large part of the gold is iu the form of larger leaves, abeeta, sr masses. The Grass Valley vdos carry, as a rule, more coarse gold than those of Nevada Oi tract. A small vein will usually carry more coarse pold tliaii a large one. and in certain .seam mines tbe gold may uccasiuually appear as a sheet tilling Uie entire seam, with bnt little quarts. Ifaesachnsetts Hill and Gold Hill, Grass Valley, were noted for the heavy masses of f,'old extracted from their veins. A specimen from the ('rown I'oiut mine, Urass Valley, contained in a 3 or 4 inch vein oi iiuarts and ealcite In sorpentine at lea.st $200 in heavy, massive gold. The coarse gold is rarely crystallized, and the forms, where (x-currinjr. are rude and distortwl. Beautiful leaf gold sometimes occurs iu cavities coated with quartz

erratals; far instanoe, in the Granite Hill vein, Grass Valley. Hr. llelville Atwood states' that in ISfiO, in the mine of North Gold HOI, he

Poranaljrsto. bj HIIIbm4. Mb H. V.TiinNt'BMtlatoB llwcaMMMr OallteBlaiiBAa.Jnr. Sel., Vol X LIX. My, Wfi. *Fmtk iJHk Itopc. 8Me Mlamkctit aT CdttMnda, p.lia. ngbth Aaa. Bait. State HlMnliffart, Ik 174.

Ore Minerals.

116 GOLD-QUARTZ VEINS OP HBTADA CITT AND OBA8S TALUnr.

took out a pocket of many tlioiuiand dollars' worth of gold, all in leafform, with bcMtifU quarts crystiils, itiul tlicy were all embedded ill a fernifjinous rnnttor. Tlie {jol'l in i-hit'Hy confaiiUMl in the quartz ; only once, in a spccitnuu from the iSouth Idaho luiue, was it noted in eaktta. OocMionally, but very rarely, ▼isible parttelea of it o-onr in the alert'd wall rock adjoining the veins.

A close association of the gold with the patches of salphiden occar> ring in the quarts ia often noted, and aeotiona will often reveal larger and smaller irregular particles of gold eooteined in tbtt gaUMia, iron pyrites, arsenical ]>yrit(-<. /incbleiidc, or teHnritles.' (IM. V, Hg. c.) Generally, however, I lie 8uipiiuret are anriteruus even wlien it is impossible to detect any metallic gold in them with the microscope. Ife is probable that the gold is here, as in theqnarta, inametaUie atate distributed iu extremely minute particles.

All qnarCi gold oontttiiia aa la well known, alloyed silver. In tbo major ity of the veins of this district the fineness ranges frotn SOO to 86U. in tiie Willow Valley east-west veins the amalganuaoil bullion is less pure, generally about 760 line. In Canada Hill the gold averages 730. In the Leconiptoii and the Federal Loan mines the luilliou has been observed as low as 050 and 07U. This should probably not be taken to indicate that the native gold oontidns 350 parts of silver, for the ore may have contained easily anialgnmatetl, rich silver minerals, an<] arsenic and antimony may also be in the billion. In fact, a Hjieciuien from the lieckmau vein, at Canada Uili, of which the amalgamated billion is only 7B0 line, contained abundant, easily viable, bright-yellow gold equally distributed in the quart/. <:iili ii:i. iind blende.

The North Star vein, as well us the veins of Maiwachusetts Hill and Gold Hill, contains high gold, averaging 860 and sometimes rewlDgSTS.' The Seven-thirty mine reports gold 950 fine, which is very nnnsnal. The Merritield and Providenee veins contain gold aver aging 8U0 line. In the Osborne Ilill veins, which carry much arsenical pyrites, the gold averages 760 to 776. In the Empire mine, belonging to the same system, the flneness is about 800. In the Eureka-Idaho vein it is 84.

Blectmm. ft pale-eolored alloy of gold and silver, with more than 26

per cent of the latter metal, has not bct n iidti-d.

Oold amalgam. — Mr. C. Uesae, superintendent uf the Odin drift mine, obtained from samples of frwh nndisturbed gravel, taken on the bed rock of the chaiiuel ami whsIhmI in the pan, a number of small hut well-rounded, white, metallic grains, associated with the gold, and which proved to be gold amalgam. Its ooonrrenoe and appearance admitted of but one explanation— that it had the same origin as tie unl.i ami onoe occurred iu a quartz vein uf the viciuity. of the ilat, rounded grains conriated, as shown under the nderoscoiie, partly of gold, partly of amalgam.

in pyriitK ami Kalma nutcri fnim the Omaha uiId: gold In anwDopyiile noted rrn the BrU; nine; in xiucblcndo noted frooi tbv Maydowcr aod titmnl mincai jpild in nlUite aotad from iIm pTorMi-nre niM.

CMipM* ronrtfe Ann. Slat* Xioaralafiiat. p.. 2X1.

U!CPMIIi.l

MDrBBALOOT OF THB TBIMS.

TeUurium mineral$. — Tellariden are probably more common than has boeti HuspcctiMl, hiir it is only rarely that they OGCOT in qaaatities large euougb to be niiiieralugicuUy iletermiDud.

▲ tellnriite <it silver, presumably IsAd-gniy, soflf sod somewhat sectile, was identitipd by Dr. W. r. Hillfbraud in a speciiiMni from the Nevada City mine, occurring with pyrite, galena, miU Dative gold.

AHaUey a tellaride of lead and silver, tin-white, with a yellowish tinge aiul Heeiile, was also identified by Dr. Hillebrand from tlu Providence mine. It iu oonHidemble quiintitics as a buncli in the Ural vein of that mine, iu the stopes between tbe GUU lbot and l,20U-fuot levels. It was associated with qnartB, pyrite, galena, and abnodant native gohl, the latter iiitcM Il with the tellurium mineral.

in testing sam|)le.s uf the uuiueutrated sulphurets from several mines for tennrinm, a negative resnit was usually obtained. The elemeatwas found in small quantities in tiie concentrates of the Nevada City and niincA. A remarkably larfje jyercenfajje of tellurium was found iu the Iduho-Maryiund concenlrateji, uuiouuting to 0.U3 per ceut; there kave been no teUarldes noticed tiraa Ihr In tiie oras of tiiat nine. Tellurium is alio Said to ocooT In the ore of the Oharonnat or Canada Mill mine.

TttradgmUet or telhiride of bismnth, is donbtftilly reiiorted ttam the Hnxohie mine,* and Mr. J. J. Ott, of Nevada City, states that a tellu rium mineral wa certainly found at that mine. It is worthy of note in this couuection that a small quantity of bismuth was found iu the conoentratea from the Providence mine.

Pi/rite. — This mineral on practically ever}' vein in the district, both iu tbe quartz and iu tbe altered country rock. In the quartz tbe mineral is nsnally found in massive form, iutergrown, without reoognizable succession, with other metallic minerals. Imperfect crystal forms are often recognized, though well-develo]>ed crystals occurring in cavities are rather uncommon. The forms shown are always a combination of cube and iicntaKonal dodecahedron. In the intend wall riM'ks sliarp. thiin'h usually small, crystals are extremely rtommon, and the cubical form predominates. Excellent and sharp cubical crystals np to 1 cm. in diameter oeenr in a sofb ehloritie rock on the dump of a shaft on the Kentucky claim, some distance east of the Maryland. Pyrite is tbe most abuudaut of tbe "sulphurets" iu tbe quartz veius, and generally makes np from 80 to 90 per eent of the concentrates.

Small massesof pyrite, iutergrown with epidoteand in.t;xi>> tite, occur in diabase in the tunnel on the Star Placer mine, west bank of Wolf Greek jii.st alive the Uiuaha mine.

JTiiroasttAThis mineral, the orthorhomhie form of iron disulphide, does not aiipcar to occur in the quartz veins. A very ]tale yellow pyhtic mineral found ou the dump of a tunnel 1,80U foet south of tbe Golden Treasnre mine was at first thought to be marcasite, and a statement to this effect was made in a paper on the Characteristic

Sm mgklh Bevt. Sato XlMNlctot.

Diyilizoa by vUOQle

118 GOUM2UABT8 Y£IN8 OF NEVADA CITT AND OBASa TALLET.

ftfttoTM of Galifornlft gold-qnartK veins.** ProfeMor Penfleld, to whom

tb*' siKH'imen was sfaown, considered it, however, ns pyrite with a marked octahedral and Professor Firsson kindly measured the fragments, Huding angles clowsly approaching those of the octahedron. Sacb aa octobedral parlaog has uot been pravtonsly observed in pjititb.

In the hhic gravel from the hoftoui of tlic NiMK-eiie cliannels concretions of iron disulphide often occur, souietiuius ceweutiug quartz grains and From tbe pale color and strong tendency to decomposition it is probable that this is marcasite.

I'yrrhotite. — This minenil, also known as magnetic pyrite, occurs sparingly, but not so far m known, on any of the normal gold-quartz veins in this district. It is ontainivl as a primary constituent in ear* t4iiii <!i;it>;ist's of (Iiass Valley, and as a secondary mineral ing niuiiy uietuiaorphoed rocks (in horufels near the Federal Loan, in porphyrite-brecda on Banner Hill). Larger masses of it were fimnd in a seam a short distance north of the Crown I'oint mine. It is here associated with vhalcopyritef pyrite, and calcite, with very little qaartz. According to Dr. Hillebrand, it contains only a trace of nickel.

Chaltupyrite.-StKAy of the quartz veins contain this mineral, but only in small quantities. It rarely makes more than 3 |)er cent of the sulphurets in the quartz. The Providence, Champion, and City mines, and especially tbe Idabo- Maryland, carry the largest quantifics of it. If is very rarely crystallized. A little elialcopyrito is also found disseminated in certain metamoriihosed diabases and [lorphyrites.

Oafona.— >Tbts Is almost universally present in quantities about eqnal to the chalcopyrite. It forms grains and irregular masses in the quartz, and is rarely if ever found crystallized. It is fiqaently rich in gold, and is always considered a good indication.**

Sphalerite (<oUeN4ltf). — This mineral is extremely and orcnrs in tbe quartz on almost every vein in the district. Tlie Providence concentrated sulphurets contain 1.6 |)er cent of ziucbleude, and in the Bcokman vein, Canada Hill, the percentage is still greater. The Idaho-Mary l:n vein, on the other hand, contain.s extremely little of this mineral. The ziucblende is usually black, with a greenish tinge. In tbe Alpine tnnnel, Canada Hill, a pale yellow variety occurs, together with the former. In the Beckinan vein and in the Oobome Hill mine the blende is mldisli brown, and often very rich in gold.

ArHt nopyritt. — This mineral is very common, but somewhat irregularly disMbnted. It ooenrs both in the quarts and in the adMntafiT altCVed country ro<-k. and seems, in fact, to the latter. When in larger accumulations it is mostly massive, but it exhibits a gi-eat tendency to fbnn minute and extremely sharp crystals when occurring disseminated in the country rock or in the quartz. Beautiful, though small, crystals, long and slender and formed by a combination of prism and base, are found in the Osborne Ilill vein. Most of the veins in the Banner Hill tract oratain abundant arsentyritci the Fedwal Loan

Diyilizua by GoOgle

Mineralogy Of The Veins.

leadiup, y'\th about 18 per Cfiit in ihf conooutratetl sulpliurots. On the utter liaud, the Proviileiice Cbuuipiou-'evada City complex of ▼ains eaRiflt Toy little of this mineiral, a sample of Piovidenoe oonoentrates cont niniiiir 'nly n.ori pei-cent. In tin' OnifH Ynllcy tract the percentage of arseoopyrite in the veius is usually very tiuiall, excepting the Osborne Hill system, which, from the Orleans mine waOHf oarriea eonsiderable quantirios of it. The veins of FoTMt Springs, 4 milso south of (Irass Valley, also carry much arsenopyrito.

I'yrargt/rite, HtepluiiiHc, and argentUe. — These rich silver luiuerals have been identified in a specimen fram the Allison Bench mine, in the United States Natimial Museum (No. M!KJ7). Hcsides these minerals, the specimen contains much pyrite, cbalcopyrite, and galena. Pyrargyrite has also been ftmnd in the Central mine, south of Banner Hill. The relatively large quantity of silver found in the concentrates of certain other mines, for example, the Providence, Champion, and North Banner, indicates the possibility of rich silver minerals occurring iu a finely divided stite in them.

Tetrnhcdritv ( fuhlerz). — On a vertical cross vein cnttiiifr across the Osborne Uill vein, near the shatt, on the fourth and litth levels, a heavy mass of tetrahedrite was found canryiniir 1 per cent of silver. The mincnil was a.ssociated with yellow zincblende and dialcopyrite. It is also from the North Banner mine,' and probably occurs iu small quantities iu many other mines in the Banner Hill and Willow Valley districts.

In the California j'old-qnart/. mines this mineral is by no means uncommon. It has been found, iuclosed in quartz, in the North Banner mine; in a nameless vein,Mariy barrra of gold, in the Mayflower frroiind : aiil in the Merrifield and I'nil veins, :it rlic I'rovi deuce, Champion, and Nevada City mines. It usually forms bunches, and is not intimately associated with the other aolphnrets; ft is not known to be auriferous. When occurring; abundantly it makes the pulp iu the battery black and slimy, and interferes with the amal> gamation on the plates. It is easily mistaken for graphite.

Cinnabar.— While no cinnabar has yet been found in any quartz vein of the district, the fm-t deserves mention that according to Mr. .T.J. Ott, of Nevada City, gruius and pebbles of this mineral were ut one time fMind in theslaiee boxes of tJieHansanitahydraalic mine. Taken in connection with the above mentioned wcnrrenceof ania];,'am. it may be considered certain that one or several of the veius iu the Nevada Oity traet contained quIekailTer. The association of qnioksilTer and geld haa freqnitly been noted in the Gold Belt.

lAmomte, or brown iron ore, is common in the decomposed qaartz of the upper levels in of the mines. As is well known, it is a result of the surlhce deconiposiiion ol pyrite.

.Pbodv0T8 Of Bubfacob Dbookpobition.

120 OOLO-QUAKTZ VEIMtt OF N£TAOA CITY AND GRAM VALLEY.

A hydrouji Hulphatt' of aluminum occurs as ii deposit from spring water ia the Provideuoe drain tunnel, in part colored blue by copper.

AmmtU* nd wutkuMU result occaciionatly from the deoompoaitiou of ebaloopyrite.

Whekals Not Oonnboted With Thb Quartz Ybins.

Metallic copper in small founded cryRtals was idso found in

the gravel of tlie Odin miiie. Tlic crystal form indicates tliat the copper wae probably precipitated fwm twlutiuu by reducing iutiueuces in the bhie gravel and the erystals formed in the gravel. Whitney mentions native copper occurring in the Tertiary channels.

Mngnrtite. — A suiall deposit of tnajnetite with some quartz is found in the diabase, uetir the gruuodiorite contact, 4,000 feet east of the Omaba mine, in Diamond Greek. The exact nature and extent have not been ascertained. There arc within the foothills of the Sierra Nevada several similar deposits, some ol' large size, and always occurring in diabase or slate, close to the contact with the intrusive rook. These occiineuccs are probably iti goiietical cnnne4;tion with the iutmsive rock and possibly formed by coutact-uietumorphic action.

Scattered fragments of magnetite are also found near the dry reser* voir feet east of the railroad Station at Grass Vdley, aod DOt flw from the granodiorite contact.

Magnetite also occurs with epidoteand pyrit,st.H probably segregated masses leached from tiie surrounding rock, iu the tunuel of the Star placer mine, feet north of flie Omaha mine.

Earthy mangaHete ore (pyrolunitc or tcad) occurs often in small fissures in the granodiorite near the surfooe. It was especially noted in the

vicinity of the Ndrtli Ianner mine.

A similar mauganese mineral wiis found as a coucretiou iu the VVest Hannmiy drift minoi oementing grains of quarts.

Ooraet.— This mineral is cv iden t ly very rare in this district. Brownish massive garnet was noticed, jnobably as a product of *(intact metamorphism, iu ii specimen of ampliibolitic rock collected iu a liule gold by tiie road, t,600 foet west of the Korth Banner mill.

WoUmtonite. — A specimen of wnllastonite in horufels was found on the Old Bauuer dump. This mineral also is undoubtedly due to contact metamorphism.

ChabnziU: — At the tunnel of the Star placer mine mentioned above crystals of chabazite were found ooatiug small flssnres in an altered diabase, filled with epidote and pyrite. The crystals are several millimeters iu diameter, oolorleos, and of the welMniown form.

Thb Mineral Waters On Thb

General featurei.— The ordinary mine water contains only a small amount of dissolved substances, aud is evidently meteorio water of the superficial circulation. In a fow instances, however, sling asoeuding

'AotitotMn Ganab. f. Ml.

hqhral watebb on tbb TEnra.

spclDg8ftre found on tbeqaMtSTelns. ThesespringH, though iieitherTery rich In (lissdlvednmteriiilH Tiorof a temperature difTcrhifi from that of the ineloBiug rocks, form a deitosit at the iioiut where they issue, and their oompoeition ia tintevMtM in some degree indteatiiifrHie the epringa to jirolmbility. the veins owe their oi i j,nii. Tw o such aaeendiug springe were noted aud their waters and exuiuiued.

The Federal Loam iNliiTbe tint is in the 400-foot level of the Federal Ijoan mine. feet east of the sliaft. The wuti-r issues from a crack in the foot wall about feet up t'roui the bottom of the drift, the quantity being about 2 gallons per minute. A considerable quantity of yellowisli white, slimy deposit was, at the time of tiiv first visit, formed ou the wall for a distance of 2 or 3 feet below the place where the water issued ; the deposit did not seem to form on the bottom of the drift. At A second visit, wlieii the water was eolle< thf wm k had been resumed in the drift, the face of which was only a few feet from the B]*riug, and tlie deposit had been swept away. Mr. George A. Treadwell, of Ncvatla City, had ]revioa8ly colleeted a hotth' of the substance, which he kindly placed at my disposal. An uumiatakable odor of sulphureted hydrogen was noted hi the Tldnfty of the spring. A sample of 2 liters of the water was filtered and bottled in the mine.

The Mountaineer mine. — The seoiuid locality is in the Mountaineer mine (Nevada City sheet), on a hanging-wall veiu called the Black Prince, about 17U feet east of the main fissure. The spring appears in the foot wall on the foot level, south of the shaft, tastes strongly of iron, aud forms a heavy yellowish-brown deiwsit. There was no odor of in the vicinity of the spring.

The waters were analysed by Dr. W. F. Hillebrand, with the followlug results :

mso

Vonb— OtRMh Mttar

Diyilizua by GoOgle

182 OOLD-QtrARTZ YKim OF VBVADA CITT AND OBA88 VAIXKV.

Dr. Hillehraml rt'iiiarks on these waters as follows:

Both Mliowi'd nil nlkuiuxi reaction, and that from r;il Loan cavf> al*io a tet fur in solntioii after filtration. Th Kodpral Loan wati r i ont:iined a mail aawoDt of black doccalent deposit, ohio; Bilics colored black by iron snl- pUd%sollwMoaMlwaMdoat. The BtaokPtlaee water oonteiiiodftlMfiMaii of siBilar black deposit containing mali iron enlphide and, perhap*, ferric hydrate. Vo Umt fnr aolnble anlphide* re!<ultd definitely in this Bample, but there appeared to lie :t litflf sulphite in both wiiters. Hvlrii;;ru Milphido wiw not present iu either. Since the wutcrH were reported to be clear when bottled, it seeuia probable that tlie fomntiou of aoluble and precipitated snlpbidea may have due to tih* Ndoeing Mtim on tlie aoliibatet Uw Mrki iaoe the mton had 1wn IwtHed many tnoatfia. aad the rarfliee of the eorke wa thorotighly biMkened. Iu view of the great um iTtainty as to whetlu r tin- )iri iir roihlif inn repreHentM iu important esBentials that ut the tiiue of bottling, a very exhaustive or thoroiiKh analyaia seemed unnecessary. It ia to be noted tliat although the depoeit formed by the water oontkina mncb naoio it ooiid not with eertainlgr be detected Ja 2 litiMt the water.

TIm VBters ate remarkably aimilar in eompositioii, and maj be eharacterized

as weak miucral waters, chiefly distinfrnislu'd by tlioir percentage of silica and carbooateB. There is roughly speakitig, from 33 to 41 parts per million of silica preeent, 175 to 226 parts of biearbonates of calcinro, magnesium, and sodium, and 12 to 14 parte of 8alpbate.s. Sodium is present in far larger quantities tban imtassium. Chlorides occur only iu very miuute quautity. Of carbonic acid there is hardly enongfa preamt to fbmi biearbooiitea wifh flie bam. Hydrogen tal. phide was certainly present in small quantities in the Federal Loan water at the time of bottling, although subsequent reactions probably masked its preeenoe.

The composition of the deposit flnom the Federal LoMi water iSy Goording to Dr. BLiUebrand as follows, in rough approximation:

Iniolnble andalllca

Pb

a. 3

1&4

.r.

Truce. U.9

m.8

Dr. Hillebrand makes the following remarks on tliis analysis:

The iMttfo waa Ailed with a black slimy matter emitting a diagnetiag odor of OKgaaia dMmapoaltloQ. The eorfc was Cavead oat with eoaa "bj UnpdaoiMd gaa, dUelly oonaiatiBg of OOt and CH. Tba amino waa aald to have bean white whan

Diyilizua by GoOgle

imiBBAL WATERS OH THB YBINB.

Mtlsetad; th aabtcqneotly developed black oolw is due to Iron milphid*. Aoido

from orgnnir ami water thr clfpoHit <-Ms'iit iall y ffrrir oxiilf with a litt! arHOiiiatc, calcium curbunalu witli u little iiiujjucitiuiii vurUuiialn. auti iiiuuaiicm' us Mni )., oliit inouti Nilica anil fraguieuls of iiiiuorala. Owing to retliiction of uJpbfttM with bottling aod thepreoence of vegetable orgaaiame, aa accurate analjaia eoold hmrt no vsIim, and the aoMHiBt at diapoaal waa alao too amalL

The presence of lead and iiiHenic in thin deposit is of interest. The organic matter was abniiil;nit, and consisted of long, stringy fiber, evidently an algous growtli, tucU as is so often noted at the mouths of uiiittiil springs.

The deposit from the Black Prince was of brown color and in qnalitutive composition chiefly ferric hydrate with a little calcium carbonate and ninth ten magnesinm eaiboiiste, also silo* and inaolabfo mattor and mnch manganese in a perozidized condition. There was also a decided trace of molybdennm. No arsenic, copper, lead nickel, or aluminum was detected, and very little sulphuric acid. Some orgauio mutter was preaentk

The Providence mine. — A dejwsit found in (he drain tunnel of the Providence mine, 800 feet from the mouth, is of quite different cluiructer. When dried, it famed dirty white masses of all degrees of fineness, from coarse lumps to an impalpable powder; some <tf it has a decided greenish tinge. Selected greenish pieces were analyzed by DTi Hillebeaiid, vitli tbe IbllowiDg (salt:

The water was determiuetl us follows:

At 110= C

Below n-duca

Parent.

1A.16

Diyilizua by GoOgle

124 Oolouabis Tbhtb Ov Ketida Citt And Oba88 Valley.

A general sample showed essentially tbe same eompoaition, ntd contained, besides, MnO in black grains. Some iMrgaaic matter was also

present.

The snbstanee appears to be a mixture of a hydrous alnmiaoDS silijj eato and Hulphute, and iobably results flrom the leaching of pyritous ora by surfittoe waters.

THE ORBSw GSKBBAL CHABACTBB.

Tliere are, in geiu'ral, two classes of gnld quartz veins between which, however, no distinct line of demarcation exists. The first embraces tboHC veins in which tlie gold is nearly exclusively connected with the nlphidoH uiul is uot easily from them by simple amalgamation and in which free gold is found only in the upper deeoniposed zones; in these veintj there is usually also much silver. The other clatis, to which Che veins here described belong, carry an ore of which the principnl v:iluc lies in the free pold. tln' relative amount of which shows no diminution in depth once the surface zuue of decomposition is traversed. The gold and the aariferona snlphtdesi some of which are always present, are embedded ina predominant quartz gangne and constitnte almost exclusively the pay ore. The country rock adjoining tbe veins has in most crises been subjected to a more or less complete replacement by

ou'bouates, sertcite, and sulphitles, but this replaced country rock is

here, if not barren of gold, at le;st very In certain deposits the

quartz is distributed in minute seams and streaks in the decumposod

oonntry rock Instead of forming a continiioas, thicker eheet; la each

cases the whole may be mined and milled. !)nt the will generally be

found to be concentrated in these narrow seams. In isolated cases the

altered country rock may contain a snffldent quantity of gold to be

treated as an ore. Instances also occur where a large quart/, vein ia

nearly barren bnt the seams in tbe adjoimng altered rock are rich in gold.

Tbb Gold.

As stated before, the gold is, speaking generally, in a finely divided

condition and scarcely visible to tlH> iKiked eye. and it is a well known £sot that sometimes a notable quantity of it is carried away suspended with the finest slimes flrom the mill, even In the overflow from the settling thinks, if such are used. Much of the gold in the narrow Grass

Valley mines is, however, quite coarse; in several mines, as the North Btar and the Bmpire, bunches of quarts contAiuing coarser gold are found in the pay shoots, generally carrying fine gold. Tbe intimate

relutioti between the gold and the sulphurets is emphasised iikwve and s

iUustrutcd on TL V, tig. a.

Ths 8Ulfhubxt8.

miTphnrots generally make 2 to 3 per cent of the ora. In tlie Willow Valley district there is <|uite generally stronger percentage, ranging I'niui 4 to per cent. TLe name conditions obtain in tlie Bmoer Hill mkI Hajflower gnmp of veins. The vdna in the trinity of the Pittsburg and Gold Tniniel group of veins, oxr(']>t the I'eunsylvania, carry a less amount. In the I'rovideuce-Champion group the percentage is high, ranging from 4 to 6 per omt, Tmt fbe ame veitm in their northward extension carry less again. The Idaho system of ea.st-w(!8t veins curry little .sulphnrets, as do nlno the Empire- Osborne Mill Hystem and the W. V. O. D., the peruentige ranging from three foarths of 1 to 8 per oent The Eareka-Idaho vein shows, on the whole, the snlaIlest ]ercentam', laiiL'ing from three-fcnrths of 1 to 2 Iter cent. The Muasacbasett Hill and Granite Uiil vetus, as well as the North Star, eany from 2f to 3 or 4 per cent. The Omaha system carries about 4 per cent.

In coui](aring these data no definite law c4Ui be deduced as to the percentage of sulpharets in different country rock. The largest peroeatAge Is found in granoiliorite, in certain Tns in the sedimentary areas, or on the confMct of hofli foniiiitions: a meditini to small percentage occurs in diaba.He and and in serpentine. Numerous exceptions make this rale of donbtftii Talne. Some veiRB of the May*

flower system in slate and .some miin s in 'raiiodioritc, sm li aS the Gold Tnnnei and Oalitbraia, contain comparatively little sulpUureitti

K(|fully donbtftilresalts areotftafned in oompuriug the percentage of snl]>hurts in the various vein systems. The only mle that night be here is that the veins of the Idaho system in (Irass Valley are poor in sulphuretM, but against thi.s stands the fact that the parallel Orleans vein near Nevada City is in places rather rich in them.

Chitriu ti)-. — On nearly all veins pyrlte the exceptions are certain mines in VVillow Vall and the vicinity of Canada ilill| where arsenopyrite or idncblende (Beckman vein) prevails. In the Merriniac and Union veins galena is said to prevail. In nearly all veins there is, besides? pyrite, galena, zineblende, and chaleopyrite. The veins with arsenopyrite are confined to certain localities, as indicated in the pages on mineralogy, bnt not to any certain kind of vein or country rocl. In fii< t, any attempts to correlate the liaracter (f the sulpharets with the country rock appears a failure. Certain veins in granodiorite contain no arsenopyrite; other veins in the same rock how this mineral in large quantity.

Contents of gold and ailcer. — The sulphnrets in the quartz always contain gold and silver. Those from the altered country rock also contain some, but are generally mnch poorer. The eoneentrated anlplm* rets, which are not quite pure, hut contain a certain quantity of quartc,

Diyilizua by GoOgle

126 GOLD-yUABTZ VEINS OF NEVADA CITV AND QKASS VALLEY.

varyiti' from 5 to 15 per ociit, r:in<;o ia value tewa f40 per ton to MTerul liuuUreU (lullurs, chieliy in gold. In any giym mine the tenor of the aulphnrete gmerany fnereaaea

with the richiipss of the ore. It is foniid, however, tliat in many of the Grm Valley iiiiueH, which carry rich ore with much iree gold, the conoeutrates are relatively poor. In the Proviflaioe and Ohauipiou veiuf;, the ore of wliicli is of lower grade, the aulphnreta ran high in gold, proLiiMy averaging not less than 5 ounces per ton. The Kulphurets <rf the great EurekiIdaho ore .shoot are uuil'ormly rich, ranging from 5 ounces of gold per ton upward.

The relative (lu-.entity of silver v;\rit's also, but only in few mines exceeds that of gold by weight. In must of the Mulphurettj of the Banner Hill diatrlet there is a oonRiderable quantity of silver, probably reaehingita maximum in the Bauner mines, where the quantity of silver }greatly exceeds thut of gold and sometimes almost e<]nals it in value. The i'uderal Loan sulphurets, ou the other hand, carry only about onnees of silver per ton.

In the Nevada City di-!tri( t the greatest percentage of silver is found in the Mouutaiueur, Merritield, and Ural veins} at the Champion and Provideiloe mines the sulphurete contain from 10 to 16 onnees of silver per ton, or more than double the amount of the gold. Hut at the yevatla City, on the same veiu, the percentage of silver sinlis, and eiualt( or in iem than that of the gold.

In the Grass Valley district there is generally only a small quantity of silver in the concentrates. A mtio of almost one-half silver to one part of gold by weight is found in tlie Kuipire, iorth Star, and Slate Ledge; still smaller quantities are reported from the Orleans, Osbrane Hill, and Maryland, where it sinks to one third or less that of gold. The concentrates of the Omaha and W. Y. O. D. carry aliout twice as much silver as gold.

There is not much definite information us to the contents of the ,scp arate minerals of the concentrates, but, as state*! above, gold may be seen occasionally included in almost any one of them. In some mines t he galena appears to be very rich in gold.

Ill order to ascertain the relative pre]>ondernnce of metals, several analyses were made by Dr. Iliilebrand of representative concentrates. Two analyses by F. Clandet, quoted by J. A. Phillips in his Mining and Metallurgy of Qold and Silver, are here given under I and II.

n.

ni.

nr. I V. I

Ti.

I

Aptenic...

TBllariain

ifMllWM fmtnetntnM Mptarrti— OHttiamd.

n.

It.

Not ilfit. Not dot.

Not det.

Tkace.

Cobalt

Cbromie oadde.

Trace. Trace.

Traoa.

.Ob

Trarr f Tract" f

.a%3

I. (iroAn Valley. AoAl.vKt, F.CUudet. n. North Star. Anitlyct, F.CIaudat. m. Korth eitar. ADoljrot, W P. HilltbrMA. rr.MiiqrlMrfL iUBdyat, W.F.HIIMnwi*.

MbnlLMB. Aulyst, W.r.HOkVnnd. TT. ProrUlMto*. Aoalyal, W. K.

Attention {."s called to the nnexjiectedly large percentage of teHnrinm in tUe Maryland uiine. Tellurium was also found in the Bulphurets from the Bevadit Oit7 mine, while those from the Empire and Omaha minefl gave negative r( salt.><. Tin-presence of bi.smiitli, cadiniiini, and poesibly tin is of interest. Chromic oxide is found only in tue Maryland mine, oocnning on the oontact of serpentine and diabme. At the time of thiBezaminiition there was roiisiderable altered country rock milled eonfayninj; qnartz stringers, and it ia not impossible that tlie OrOa may have been derived &om that.

The Valuk Of The Ores.

Uigh-grade oren are found on the narrow veins of the Banner Ilill district, even reaching 950 and $1€0 per ton, but a good average of the mines working on a large scale would ])robably bo l.l to *20 ]km-ton. In the JSevada City district the average would probably also be i5 per ten, though there are great variations, many of the minw veins containing small bat very rich pay shoots. In Grass Valley the averagfe tenor is di-cidedly higher. Fair statistics are available, from which it is clear that it is in this vicinity $20 per ton. No law can be deduced as to tfte tenor of the ore in different country rocks. Bich ore hoots appear to occur in all formations.

The value of the free gold obtainable by simple amalgamation is generally mnoh higher than that of the gold in the snlphnrets. Barely, as in the Korth Banner, does the gold in the snlphnrets equal the qnantiiy of free gold.

Diyilizua by GoOgle

128 aOLD-QUARTZ VBIN8 OF NEVADA CITY AND OKAfifl VALLEY.

The viiluf of tlie always greatly exceeds tliiit of tlif silver; oonnted by weight, ttiere re ouly a few luines iu wbicli the silver upproaches or equals tbe ireiglitof the gold produced. Among these ace many of the Banner Hill siud Willow Vallt'y mines. The ratio hetwen gold and silver hy wei},'ht, though variable in the -anie ndnp, is, for instance, 1 : 1 in the Lettumptuu, 1:3 iu the Nurth Banner, 7:4 or 5 ia the Moanteineer. In the Providenoe md OhAmpton mines it appean to vary from 5: 1 to 7: 10, the latter being the highest figure for ailver

These figures are derived from the tabled of production oi the mines in the Mint Keports. It is believed that the assay values would show a somewhat iiirher percentage of silver, Ibr the reason that in treating argeutilerous gold ore a relatively larger quantity of tulver is lost in the tailings.

The upper part of the vein near Uie snrfhee is generally deoompoaeifl

and forms a reddish, erunibliiig or soft mass of linionite and quarts. The process consists, as is well known, iu an oxidation of the sulphides, with aooompanjing liberation of the gold and a general loosening of the texture. This decomiHjsition extends a variable distance from the surface, very seldom, however, more than feet on the Incline of a vein dipping 45 or below a ▼ertical depth of loO feet. On the other

hand, it in common enough, especially in veins with little sniphurcts, to find fresh ore almost at the surface. The process i-*. on the whole, of slight exteut and compared with other mining districts. In oonseqnenee of the liberation of the gold ftom the solphnrets, the anrw face ores are easily reduced, and in consequence of the removal of other substances than the gold, they are also generally richer than the fresh ore below. In this process the stiver ia also partly removed. The decomposed croppings of the Grass Yall veins often contained {torn $S0 to $3()0 per ton, while the average tenor in depth is firom $20 to $30. At present very little of this surface remains.

Differing HnteHma. — Four distinet kinds of stmetme ooenr in the ores:

1. Massive structure. Massive qnartz with snlphnrets in wholly irregnlar distribotiou. law can, as a mle, be discovered in the order of deposition of the different snlphnrets. This stmctnre is very common.

2. Banded stmctnre by deposition. In this somewhat less common

form of structure distinct bands ..r streaks of snlphnrets lie in the generally massive quartz parallel to the walls of the vein. In the Providence shoot of the ITral vein this structure was beantifhlly shown, and is mentioned from many other places in the detailed descriptions. No definite mle could be made oat as to the disiribntiim of the different

Bupbbfioial Altsbation.

SHX BTBITOTUliB OP THB OBB.

Tbs Orbb.

snlphidea, all freqaeatly occorriug mixed iu one streak. It has, however, been noted that the ohaloopsnMe Is, often at least, later than the galena and pyrita The banded stmctnro jn illiistratuci by PI. VH, fig. a, showing Omaha ore with banded pyrite on the left. In smaller veins both of these structures are ftequeatly found with druses and transitions to i'omb structure. (PI. VQI, fig. a.) Symmetrical deposition of bands on both walls is not oCtoii seen, probably on account of tin-fiat dip of the veius. The sulphureta occorriug iu banded form by tioii are ywy often shattered by enbiwqiient light movement. Biieh a shattering may, to some extent, be seen in the R])i ( iim'ii fnim the Omaha mine (PI. VII, tig. a), but in far more cbaraoteristic form iu the speuimen diown in PI. YIII, flg. b, illustrating ore ftom Hm twentieth level of the Empire mine. In this siiecimen minute speekeof gold maybe seen plentifully sprinkled in the pyiite atul galena.

3. Bauded stractare by subseiiuent muvemeut on the vein, or ribbon ilrueHure proper. This ttum extremely common, bat has rarely been rccogiiized as due to a sheeting of the vein after its deposititni. Tlio explauatiou generally given for it is that it is due to deposition or to reopening of the vein. The atraetnre is eharaeterized by the branebiug of the cracks iu detail and by the drawn-out streaks of sulphnrets noted along the fissures. Gohl is freiinently found in platen* and coatings along these slieets, evidently deposited as a secondary concentration. The mioroBOopieal stmotnre givta conclusive evidence as to the crnshinp of the (juartz.

Pis. IX and X show the ribbon atraetnre of the Merriheld vein, Providence mine, stopes between thirteenth and fifteenth levela. 9%e vein is 20 inches wide; 12 inches on the foot wall show massive white qnnrtz with some sulphnrets, and with small cavities in which crystal points protrude. The next 5 inches are partly shattered, and a strong sheeting Is devekkped in tiie last 8 inohee nwt to the hanging walL Again, thehrancliing character of the cracks atid the drawn out strealcs of pyrite and galena are characteristic; uo gold is visible with the magnifying glass. Only the upper half of the vein is represented on the photograph.

Filially, the ribbon structure, in contrast to the banded structure, is illustrated in i'l. V'li, hg. a, from the Omaha mine, fourteenth level. Free gold is seen with the magnifying glass both in the banded pyrite and galena and in the pyrite along the Assures to the right.

4. Banded structure by reopening. A banded structure is sometimes met with which is kparently due to the reopening of the filled vein and the deposition of a new layer. Structnres due to this have been noted from several places, but they are not always . asy of identitication as such, for an interruption in the vein-lilling process might have produced a very similar reealt. A good example of this structure is shown in a vein l A inches wide from the Oslvorrie Hill mine. The vein is divided iu two by a surface covered with small crystals of araenopyrite, and each port shows independent comb stmetnre.

130 aOLD-QVARTZ VBIMS OF NBTAIU CITY AMD OBA88 YALLBT.

Mierosctipie/eaturM, — The normal vein qnarti htm yeiyeliftTaeteir iMic granalttr, hypidioinurphic stractare, wbtob in its essential fiMfettvaa

remains tbe same, though the dimenaionn of thf grains may vary greatly. The grains border with irregular liucH, partly with oryatallograpbic outline and tke larger grains an penetrated by smaller, moro or less perfectly dfveloiu'tl quartz crysf als. This is illns tratedoii PI. IV, Ug8.saudi. Miarolitiu cavitieii, in which the points of orystals project, are common, and are filled with ealcite or opaL Tbe gaienai chaltHipyrite, and blende never show crystal form, while eabea of pyrit4 lire seen, and araenopyrite nearljr alwajs appean, with crystallographic outlines.

Other minerals than qnarta are rarely present Oalcite ooeasiwiaUy apiwars, and sericito also, the latter ( (tiifiiied to the vieinify of fragmeuts of country rock and never embedded in the massive quartz. Shreds of ehlorite ooeasionally appear in tbe quartz (Maryland mine). Barite and flaohte do not occur. Feldspan, aoisite, and epidote h§ve not been in the vein quartz.

Fluid inclusions are extremely abundant; they are usually small, of irregular form, sometimes have rapidly moving bubbles, and are, as a rule. in different jvlaiies in adjoining grains; a on crystallographic plaires is sometimes recognized. lu other cases the indnslMis are eontlnnons aoroas adjacent grna and show a peenliar radiating arranjenicnt dependent on the sulphides in the quartz; long-drawn form ur aji'angement parallel with the walls of the veins appears only exceptionally. The bubbles tested did not disappear on heating to fSOo 0., and it is not pvobaUa that they contain oarbcndo dioxide.

No recognizable relation exists between the Huid inclusions and the richness of the qtuurts.*

Durinr the earlier investigations of Davy, Sorhv, Brewster, and Vogelsang -a great many siieeiniens of vein quartz, with large fluid inclusions, flvm Schemnitz, Ilunprary, Onanaxnatof MezieOi and other localities, were tested, and the results showed tbat the Contents were chietly solutions of ehlorides and sulphates in water.

A liu'ge quantity of clean quartz with bat little pyrite from the Merrifleld vein, Providenee mine, fifteenth level, was examined Ibr soluble

salts by Mr. Oeorfie Steijrer. Five hundred Kranis of the powdered rock was treated with cold water for two days} then heated three hours on the water bath and Altered. This gave a milky filtrate whtflh amounted to about 1.000 c. c. The filtrate was evaporated to 60 o. and filtered again. This filtrate was ])erfeetly dear, and its analysis is marked B. The residue on the filter was examined separately, its analysis being marked A. This residue oontalned amne earbonatea which had evidently been in solution.

or. W.M. (NirtU. Trniin. Am Inl. Kng. VL ZVXIXi IM p.M. llMHkiucb, rb>'aio|[raphlv der UlueraJieD.

Tre Orbs.

A.

B.

ao,

CaO

a

Is

Js

U

a..

Tfip result sliows tlu' presence snl]>]mto8 nf calcium and alkaline Bulphateti, together with very little chloride. The sulphuric acid could not have been derived from the pyrite, for tiiere la eearoely eay iraii present. In all the sohible salt* were conbiiiiod in the fluid inclosionii. Some silica, probably amorphous, has also been diatHtlved, aa well as a little oarbooate.

The occurrence of carlKniic acid has hoeii slmwn by Dr. Henaoldtill a qpedmen of quartz from the Tiger mine, Calaveras Comity.*

It to extremely common to And the vein quarts broken and emshed along certain linee, and the appeamncc of this crushed quart/ under the microwope is identical with the efVects of cmshing, so often described, iu massive granular roitks. An excellent example of this structure ii shown ou PI. VI, fig. a. The crossed niools bring out the alight diflerence the optic orientation of the rrushefl parts of ea<'h grain. Actual fuultiug has lakuu place, and along the fault lines a crushed aiITegate of new, lagged, and irregular quartz grains is formed. If this process is carried somewhat farther a sheeting of the vein will result, and along the planes broad streaks of secondary quartz aggregates wUl be formed. ew shght flaeuiee are sometimes formed, and by a process of secondary concentrat ion jrold and sulphides maybe deposited along these planes. To this the frequent richness of the ribbon quarts is no doubt due. The masses of anlphides in the way of the fractures are broken and pressed out in lODgstreaks. PI. YI, fig. ft, allows the structure of the quartz from the large specimen of ribbon quartz illustrated by PL IX. The section is made from the quarts next to the wall, and shows well the contrast between the fresher quartz and sulphurets preserved on the left and the flyer aggregate structure of the quartz and pressed form of the pyrite on the right. The partings in the ribbon quartz may often show a parallel striation. Under the the ribbon structure by sheeting is distinguished from that by rcopetuM;: or deposition by the fact that in the latter there is no indicat ion (if pressure in the quart?., or at least only on one side of the dividing ])iane, while the quartz ou the other side is deposited as a mold on the parting plane without showing any dynamic disturbance.

Papar bjr W. X. OowUa qmtaA cWf*.

Diyilizoa by

J

Plate Vi.

THIN KBCriOKS SMOWINO STBUCTDftK OF OKE.

FicKo. CnMhad Tvin qnrti and iaoiptoBt ilblioii-vtnietiim; NvmU Glljr bIm) 134 N.C. Magnified 15 diauieten.

Crossed Illci'l:!.

Onljr quMrU.

¥m.h. Ribbon -atwetUTB, ahowing crashed quart/ nnd prsMod pyrite. OrigiDsl aggiagataa of qnairti and pyiita to tha lafk. ktom aparimim ahowu in Pis. IX aod X.

M iginficii 17 dianalaMi

CniiiseU liiculs. Black anaa, pyiita. All otbar anaa qoarta.

m

uiykiuu Ly

PLATE VIII. sraoiMBm raownro snucrvn or vmm.

Fro. m. Tbbk Bcction of I'-indi ipiurt]! Henni in iliorite; California lulne, Dead Mans flat; 143 G. V. (Quarts ahowa comb-atniotim. The wall rock a baaio dioiito witb pytrhotiM, alrairiiiy next toTaia loalelta aarioitak and pjrito. Nalatal size.

FlO. t. Vein quartz ; Empire mine, twentieth level; 185 O. V. Showing crushing of pyritoniMl Kniinia, ud TCOdBeotiag later qmnte aeum. Kataral sise.

Flu. e. Vato qnarts; BauMirtaliM. 8lMwliiKshttitogof black arglllltalijqiuvfai aaama; pyrite developing in the argillite, but not in tlio quartz; farther, biownifih (weathered) crbouati depoeited nest to the argUUte in tbe aaoiH. I!> ;iiiuiiigor matMOBBtiealtMstlmiiOTanBtbjblieaeliiBgoftlw black argilhte. NatDiBlaiaa.

Specimens Showing Structure Of Ore Nat Size

Plate Ix.

▼nw QUAjrrz, mamwava vxm.

Tain qasrta; ManrUlflkl tId, Pwridoam mine, flftaoBth label, wmdi. VMn 2 feet

wide; only ono-bulf of it, adjoining hunting wiill, ia roprMicntcd. lialf muMive qiiiirU; upper half sbuwiug typical ribbon-btriictiire by shoetiug stibwquent to deftoaitioii. Showing liimeUqg flame md pWMd pjTlltfli. Two-third* of uatunl aix*. MS

Plate X.

TKm QOAHK, MBUUriBLD VBDT.

Specimen from MerrlHrld vein, lineenth lovd, nonth; howiag tjrplMl llbbOIMtniiK tan with brancbiug fiiMurea and preweU pyrites.

Oigiiizea by

SPCCIMCN FROM MERRIFIELO VEIN, SHOWIM STRUCTURC OF ORE. NHuril au*.

C H A i' T K II X.

CHAXGES IN THE ROCKS K TO PIS8VBE AND VEUf

Formation.

Obnbral Fbaturb8.

Along veins tbe rocks show notable inechanit i' mmI i li<-iujcal changes. The tirst ia shown by liiu's of frat-ture ami by breccias, cemented by quartz. It is also, but more rarely, shown by wideneaehing medtaoical deformation of the rock, prodnoing sehiatoee and slaty structure. TImclmractcr of the Assures as integral i):irt.s of extensive sUeeting aud jointing iiu|)lies less of a long-contiuued and intense movement on the shearing planes, and more of a sndden break or crush, with the format of a single fissnnt or of brei-cias and braiii liiiif vcinlcts. Tlic chcinicil lumge is of nnifiirrn churn<'ter, and is always present, but may be more or less emphasized; its universal ocenrrence and the mineraloftlcal character of the process point nnmlstiikably to a chemical rcar'tinn and interchange of substance bef ween the ruck and some timid once tilling tbe fissures. In other words, it is a process of aobatitntion or metasomatic replacement.

Mechanical Alteration.

The breaking: aTid brei ti.itin;,' of the nwks along the fissures have not, as a rule, produced au extensive meuhauical alteratiou, though in coarsegrained rocks the eonstitaents are often, under the mleroacope, seen to be sDnit'what crushed, and the (|uart/ grains often acquire nndnlous extinction. More rarely appears a schistosity of tbe rook next to tbe -rein, produced by the shearing force exercised in breaking the flsaare and also by the grinding of the walls against eaohotiier after the break.

It is along tlie Merritieiil and Cral veins, on which, as shown in tbe detailed descriptions, extensive faulting has taken plai-e, that this schistose stntcture is developed on a large scale. This is especially well seen in the Chanipioti. Pnivideiice, atid Nevada City mines. The zone in which the scbistosity is develo)>ed is from a few feet up to 2U feet wide, and in it one or several quartz veins may be contained, as explained. The grantwliorit** is converted to a greenish-gray rockf breaking in Hat irreguhir fragments, by gr'enish faces with greasy feel. The planes of scbistosity are curved, and the structure is produced irregularly, less altered masses alternating irith thoroughly schistoae streaks, chemical alteration of these rocks is

146 OOLl>-QUAltT2 VEINS OP NEVADA CITY AND GRASS VALLEY.

intense, aiul will be later. The niecliaiiK-al tlefuriiiatiuii is ecinally prononncd. Tlie qnarta graiiia ure completely tbe wlidle ;ii:;:r<'i:;it' of f!ie fiiaiHxIioiitc is ircnisli, fiu-gruiQeU,ullotrioiuorphiu aggregate, often witti a tioiuewbat splintery fracture, dmwn out in long streak and atringera. The carboiiaceuiis 8chi8t of tlto Ural foot wall is equally crnabed, tlionh tlie eflect on tlie individiiiil fjraiiis ln-r( no! visible, ovrni>; tu tln' ori'iiiiil rtiii'iiess (f grain. Tlie re.suUiiig mass id a black, Kuit rm-k with irregular and carved black and abinlng planes of acbiatoaity, nincb more unregnlar, in fiMst, tlian tbe original planes of sebistosity of tbe rock.

Chemical Alteration.

OKNKBAL FEATrRBB.

Tbe chemical alteration which ttie rock next to the tjuart; has undergone is developed with very different intensity. In some mines, indeed, like tbe Mountaineer and Ouialia. soniftimcs also in the Eiiipiti' ami Korth Star, comparatively fresh rock lies close up to the vein, while in others the xone of alteration may be several it wide. Tbe most extensively altered rock is usually the brecciated mass lying between two closely approaching fractures or walls. Tbe resulting rocks, otten eutirely different in from tbe fresh rock, usually have a yellowish' gray to gray or white apiiearauce, aud frequently a greasy fed. Tt is oasy to find all kinds of transitions, fmiii tbe incipient to tbe nuKst advuuctMl alteration. All rocks are subject to this alteration, even tbe sflioeous argillite from the Federal Loan; in carbonaceona fissile ar;.'illites, however, sitcb as in the Merriiuao mine, tbe alteration is very slow and cbiedy confined to the of pyrite. All minerals are snbjert to it. even the quartz of the anodiorites.

MINBUALOUICAL CIIAUACTEH Ol ALTEKATION.

The clianjres in tbe nn-ks are ebielly <lue to the furnialion ut' three classes of uiinerals: {Ij CarbonnftJi, chielly calcite, pure, or mure frequently with a small admixture of the carbonates of iron and magnosinin

, flic loniici- ])i iulnciii;r a brownisli color in weathered frainents, lear veins in serpentine the wagnesiuui imbonate pre\ ails, (li) PotmfttiM mleos, nsnally in fine-felted aggregates of wavy fibers, with often silky luster; the name sericite has been for these niicaceousaggre' ' gales, according although it is probable that the composition varies little if any from that of normal muscovite. It is hardly ever possible to obtain the mineral in a anflBdently pure state for analysis. OHkt potassium iiiii as ( iiiriiig connected with altered wall rocks arc the so-called iiiariposite (cf. p. 110), which is colored green by chromium and is probably identical with fuchsite. A vanadium micai roscoelite, also occurs on veins in Kidorado T'ounty. (3) iStepAtdfli; pyrite is extremely ubuuUant in sharp, cubical crystals, and

Chemical Alteration.

U7

in sninc iniiics iirsoiuipyi itp also ai)]ii :ns in idioiiiorpliic forms, ''nlcitp or quarU riuis ufteu surround the cubes of pyriU:.' Ho utlier sulphides have been obwrved. Psrrrtaotite, which is estranely common as a remit of nietauiorpbit; jiroi-essex in certain ro<-ks of the district, is found in thf alt-n'd wall rork. Abiiiulaiit cxamph's show that it is trauslbrnied into pyrite when within the intluenc-c of the fluids circulitting on tbe Assares.

Besides these irin( i]>:il rronps minerals others oi rnr. Smull ({oautities of chlorite huve hveu observed, but the process is ou the whole not fikTorable to the development of this mineral; titanite (leucoxeue) is firaqnently in* -i m. diu-to an alteration from ilmenite or titaniferons niajrnetite; ehmuiite has been observed : magnetite is absent, uud ieeois to have into ferrous carbonate or perhaps also into pyrite.

Tills process is one of metasoniatic iTiferchange — that is, "an interchange of substance without necessarily involving, as does pseudomorphism, the presermtion of the original form of the snbetanoe or even of its original voluine."-'

interchange or replacement, in a restricted sense, necessitates chemical action between the mineral attacked and the solvent; of siieb character are, nearly exclumvely, the here described. In a wider sense, it also inchules iinx es-ics by which the original mineral is dissolved us a whole aud a new substance deposited in its stead without chemical action between the two anbataoces, as, for instance, in the case of replaciiiL; alcite.

Ke|)1accent by silica is not among the prooeasea here recognized. It should be borne in nund that a rook shattered and Ailed with qnarts seams is not an evidence of metasotnutic reidacement by quartz, nor is such a a quartz vein in juwess of formation. In a mineral water containing carbon dioxide, sulphureted hydrogen, carbonates, and silica, the former three oomponnda will vigorously attacit, by chemical processes, the minerals of any ordinary rock, and form new eouiiuiuntls, while the silica Is inert and plays a passive role. It has not beeu noted that the silica in the mineral waters forming the \'ein has replaced iiny of the rock minerals. Most of the silica set free by the process of carbonatization has probably beeii removed and <lcposited in the tissures, while some of it — es|)ecially where thermal waU-rs permeate whole rock masses and no Area docta exiat— may be deposited in the altered rock as secondary afrrrefrates. If a sil!cili< of the wall rocks is found at any place in the California gold-quartz veins, it will probably be in easily soluble rocks, such aa limeatone.

It is necessary to separate strictly the quartz filling in the veins deposited in open spaces from the metasomatic oonntry rock. Tbe

Tto MM witk wkiek Imf tdioirpbic trjtal* et pyrito BMjr 4valet la oaruia rocks, toek uUm -Ifiwiim. Mta. V. aOwl. 9mmr,Ywt. ZU, p.Mi.

148 OOLD-<iUAKTZ VEINS OF NEVADA CITV AND GRASS VALLEY.

latter, however altered, bears evidence of its metiisomatic cbiiractiT, iDriiile tbu lurmer, in its stractore, clearly iudiuates a crystallizaUou iu open space.

Ill the ordinary course of the nietasomatic process, as here .sliown, augite, horubleude, uralite, feldspar, aud epidote are tirst vigorously attacked. Proceeding along cracks in the minerals, a finely felted caldteand Hericitd u<;;;rt'i<:iite invuden the gndos until the replacentMit w complete. Tin' hornljleiide is sometime}* dirci-tly into coarse foils uf muMcovite, aud iu the feldHpar grains there is often, ulsu, a distinet tendency of the sericite flben to pMmllel arraiigement, finally re.siiHiiig in tlic foriiiiiit; of larfro foifs. An interlacing stnictnre of mica foils with the iutersticcs tilled with calcite is aometimes met with (Hederal Loan). The qnarti ia alao attacked, Imt with bmmm difficattjr ilian the otSnr minerals; from many localities then la oneqaivocal evidence of a process of fjradually eating awny the quartz. In lig. b of PI. V the resulting aggregate is chiedy com|)osed of calcite with a little sericite. In other slides the product is chiefly Berieite. The relative prepondt ranch of the carbonates and tlic mica is siihjcct tovariatiou iu the Hame miue. As the examples below iudicatc, they ttsaally occur together, bat ooeaaionally (analysis from the Idaho) the carbonates may entirely prevail, or (analysis from the Osborne Oill) the rock may he :iIiiiost ciitiicly c-omposed of sericite. Tlie qiKintity of pyrite is usually large, aud il appears us if the pyrite were derived mostly, not from the magnetite, hot from the fBrroua ailicatea.

In aildition to tin* nu'tnsoniaf i<' iilfcration, tlie rock is vi-ry commonly traversed by small tissures, which );*'iieraliy are tiileil with carbonates CT a mixture of oarbonatea and ijuart/, more rarely with quartz alone. Thia oharaoteriatie ia often very prominent, and it seemaat first glance Mtrange to see the quartz vein adjoiued by a rock tsavarsed in all directions by veiuletsof carbonates.

Tlic chief and marked cliaracteristics of tlic altered wall mcM are the introduction of carbon dioxide, sulphur, and potassium; the latter is especially emphasized, because the prevailing rocks of the dlatncta are decidedly richer in sodium than potasaiumi aud the conclusion is unavoidable that uot only has the sodium been leached out but sium Mutually introduced in the rock. Analysis I of the altered wall rocks is espeoially instmetiva compared with the analyses of ficash granodioritos.

The {)ercentage of silica is lowered by ut least 10 per cent; the aluminum appears £sirly constant, as does the iron, though part of it la c( un ci ted into sulphides. The calcmm in some cases remains con- BtiUit, while it is considerably increased in most rocks; the magnesium IS not mneh changed. Sodium has been extensively removed, ntaiiie acid remains oonaliant, as does the phoaphorloaddof the apatite.

Bvbbtancbs Lost Or Intuoditced.

Chsmical Alteration.

In snnir analyses the pi-ewnce of hariiim iti not prently difforiiif; qoautities fruiii that of the fresh rock is of iuteresL Water, above llOo C, 18 present In pretty constant qnantitjr, rangiaf from 1 to 3 per rent : extensive hydration has cGrtainly not taken in the case of altered aerpeutiDes there is a distinct dehydratiiMi.

Analifttn of altertA teall tvek:

J

m.

Vu.

Vui.

B0.16

4R.74

' TIOj

1 L6S

.1

Ai.n.

l.Ot

. i:t

FeO

;i4.96

.Vs6

&87

i.r.it

Km*.

.U9

Nonn.

Souv.

Nolle.

t.io

&44

' 11.10

23w86

&amp;S5

SrO

Trace.

TrnrH f

Trace.

None.

bo

Trace.

Trace.

None.

Tiac*.

HgO

i.av

K;0

S.7I

8.Ts

' 4.28

4.Xs

Tnca.

iibor*

2.Ss

S.M

PiO.

SOi

Nom.

Tram.

S6.9T

I. HvtleroanMiii tiinnrl (43 N. C.|, iterlrnd irwin (nuxMllorlta. Aaalyut, Georf* Sleljiar. II, Prvrldriic-n tulur, fruit vt-lo 2a8 N. C). derired from gniaMllurlla. AnjUyiit, W. P. HUleltnadin. rrovideoce raiDe. back vrin (313 X. C), dvrlmd from fruMdiaiitoaad Mhlak Aaeljst, W. r. ItUlvbraod.

IV. Fi'drral LiMtn miix- i3 N. C.). Aaalyat, Gwhk KUtjger.

V. Idaho. ICth lrvi.1 (IM O. V.), itorivnl fnnn arrprDUntt. ADlj-t. W, F. UllU bmnd. VI. Xorlh Str mino (IW <J. V.). dvrlvnl rmm nriilits diahM.-. Anslynt, VT. K. Uilh-brand. VII. Kmpinmine iLM G. V.I, di-rivrtl fniiu gnui'idlorilo. .\nlyiit, Grurgp SU-iger. yUL Oaburnn Hill mine |B3 C V.). drriTed fran lliw-grand wtndalaiw. AtMtyvUUevrft SMgnr.

Tbaae determlDatiaDs of FeO were MMtla&ctory on socuunt of FaSg.

kKi< Ik ) nut l<>oked tar ttmwimn, bat eNtafailr pr>— it im mm tlum tnMM.

▲pproxinule.

l.')0 GOLD-QL'ARTZ VEINS OF NEVADA ( ITY AM) fiUASS VAI.LKV.

For fsompariHon the foUuwing ftualyses of fresh rooks are ttpiieuded:

SiU,

no.

Al.o

Fe.o

FeO

MdO

C0

SrO

MsO

KjO

Li.O

nyO Iwlow c

Tf n abAvalllHC

Co

liS,

F*;S,f

Carbou uf organic matter .

Lost

s.aB

M.01 a6.08 Trace. Trace.

in.

lasi

Tnoat

Tne*.

Trace.

I. 1&quot;

Truce.

Tracp.

3.16 ' .68 ,

W..V. 100.37

I. OnUMxIioritr, Shurtli tl learn. Xrvili Cily. .\nuhal. W. K iltllrbruiiil. II. DiabMc, 600 fn't itoutb aonllirjiat uf Murylnml Hliiiri (IL'I (i. V.i. Analvnl, II N. .Stokr-x. HI. SUiiWMie Mnewlwt Federal Loui (3tl N. Analyst. W. t. BNMrtBd.

Pet()> an apprastauM* Mir haaanaa af inaawiaa af aalpliliiaa.

6 BwautK of t hn urxun ic matter aii4i aaiaUa aapfelda tha EM> aaulil aat ha all Irtm tSXvr ilnlurilnn o' tbat nrmliHl for aa FMk Tha fMl ghas iv where tliere U much |iy rlu< in perhapa oaljr aaar tka traA. Aajr error ia aMk oaaaa af

On the whole, the analyNe.s hIiow ii rrlsitively .small atnount of KmcIiiiir of iiy snb.Htaiice except silica autl tiodiam; large quantities of the latter have beeu removed.

Bxahplss Op Altbrsd Obanodiobitb.

A from tlio Ucllefonntaiii tuiiiiol. Banner Ilill tract, is of a yellowi.sli-fjriiy niottlotl color and pfraniilar strm turc, made evident by quartz grains and darker spotH reprtHeiiting reiiiaiim of horubleude. Sharp, ottbical cryatals of pyrite abound. Under the microeoope fhe

Ohbmcal Altebatiok.

graoitio Btrotttiire it Tory clear. The hornblende sad mica are con. vertd iuto iargb muscovite foils. The black icon ores nre coii\ i ttd into milky ojniqno substances. Tlie fpltlspars aro roniplcti'Iy cliiiii;;i'd iuto u line graiued sericitic aggregate, urtcii showiug parallel arrangeneiit of the fibers, or, alNO, two systems of fibers at lirlit aiifrl'"-*. Smaller inasso-i of oatcitf lit' bet wcimi the sericite fibers. Sharp cubes of pyrite lie in the aggregate, cuutaining included masses of the 'mieaoeons mineral. There is practically no fsldspar left, while many of the quartz grains have retainnl their original form. In other grains the serieite is undoubtedly corrwling <lie fpiartz frrains in exsictly the same uianuer as showu from the siieeimen 111 C. on PI. V, fig. ft.

Analysis I in the table shows tlie compoettion <rf this fy]>iea1 ntek. Estimating that there is 25 per cent of nnaltered qnarta in the roclL, Che eonstitnents may be oalouUted as followB*

Clciniii carbonate ...

<-arboiiatn

Iron carbonate ,

Pyrite

Apatite

Titauite

Qoortt

Serieite

80T 6Llt

J

The composition of the sericite may be ciUculated as follows:

This correspond.s fairly well to an acid nmsuovit, that the FeO is too high; this may be explained by the onoertainty of its deCer mination in the presence of so much FeSa.

152 0Or,I) yUARTZ VEINS OF NEVADA. CITY AND GRASS VALLEy.

Tbe crushed and BcbistoBe grauodiorite from "New Shaft" on tbe Ifenriileld Tin, Providence mitio (111 K. C), U a grayish green mottled rock with curved phiiies of schistosity and grOMgr feel. It eR'ervesoes Btronply witli hydroibltn ic; acid. The feldspars ftiid hornblende are entirely converted to uiicuceuuH uggregutett, with irregular patches and veinleta of caldte. Maeh of the qanrtz remains, bnt is marly eveiywhere, in flu"! pnxres.s of rotivcrsiou to calcitf, mixed with ii httle sericite. The (iiiurtz is greatly crashed and drawn out lenticular aggregates. A portion of Ibis slide is illostnted In PI. V, fig. b; tbe quartz is somewhat crushed, bnt is still plainly seen to be composed of only one or two orijriiial priiins. The small calcite (grains forming abundantly along or near the cracks in the fresh quartii are very characteristic, and the whole is voqaesttonably a process of metasomatie replacement.

In a tissurctl quartz grain the individual cracks might be filled with cfllcite, and thns the appearance of metasomatie replacement created.

The criterion of the replacement is the inward progression of the new aggregate.*), resulting iu irregular and ragged masses, nud tbe fact that the separated portions of tbe quartz no longer fit together.

Specimens ftom the Merrifleld.vein in Piovidence mine, thirteenth level, show the same grecMiish gray Tnittl'd and seliistose rook, some* times almost fer|)eutinoid in appearance; iu places granitic structure is still visible. Small seams of quarts and caldte traverse the rock, and sharp}' defined cubes of pyrite lie in it. Under the microscope the rock is very similar to the one just described; the quartz is in places drawn out to long strings of aggregates; calcite seams surronixi the pjn-ite; the feldspar is largely converted to sericite with <-alcite. A little chlorite is also present. The analysis of this rock is shown under II, p. 149. It is es.seiitially siiuiliur to 1, except that the altmitlon bas scarcely pcooeeded so far, as is evidenced by the greater percentage of IMgO, not needed for carbonates and to the chlorite, and also by the lai-ger remaining percentage of sodium.

The altered granodiorite from the Emigre mine twentieth level, occurring close np to the quart/ (l.'ii G. V.), presents the same appear* ance and eflervesces greatly with acid.

Tbe microscopic character is practically identical with tbe specimen already described, and Analysis YII shows that tbe composition is also ]>ra(;tically identicaL Many small veins of quarts eat the aericitic aggregaU'S.

Bzamplbs Op Ai.Tbimcd Oiabasb.

A apeelnen of tha altered porphyritic oralite-diabBBe the hang*

iiig wall of the North Star vein, twentieth level (10 (i. V.i, ia ii prayish green rock with fine-grained grouiidmass and small greenish feldspar crystals. TTndw the mieroaeope the rock is shown to be fbr more altered than its appearance would indicate; the diabasic structure of feldspar grains, in part interlocking, in part lath like, is stdl visible but greatly obscured by an all-iiervading aggregate of sericite, lulcite,

Chemical Alteration.

aad cblorit. Grams of titauiu inm ore or ttUDiferous magnetite are in process of alteration to a Unish-white anbstanoe, probably tltanite.

The partly cnished rock between t he walla of tiie vein is greenish* gray, ofl aixl dt iise, ami is traversed by nsirrow veinlets of 'arloiiate, qaartz, and pyrite. Tbe alteration has here gone further uud the orig* inid strnctore is aoaieely racof disable. Tbe aoalysia of this rock is

given iiiider VI. from which it is apparent that a great quantity of calcite is present. Tbe analysis may be roagbly calcolated as Ibllows:

Caicite

Magnamta

Pyrite

TKulta

Per ornt.

4Skl5

3S.0O

Tho sericitc is not pine, as is eviilenced by the strong piTcentafro of MgO and FcO. The latter is very high, and it is not certain to which mineral it belongs.

Tito diabasi> of tbe banging wall of the Idaho- Maryland mine is not altered to such an extensive degree as the size of the vein would one to suppose. It is a soft, green, cbloritic ruck, containing only relatively amall amonnta of earbonates and seridte, bnt there la mnc inm pyrites in sliarp crystals np to aevoral minimctors in diainctiM-. Tlu* microscope reveals a fairly well preserved diabasic granular structure, veiled by flhns and maasee of chlorite} tbe titanic iron ore is converted to milky opaque aggrtes.

Tbe serpentine of the fiwt wall of tbe Idaho-Maryland vein is, in places, greatly altered. Specimens (147 G. V.) tbe sixteenth level near tbe shaft show near the vein a grayish green, distinctly schistose rock, soft and with greasy feel. At tirst glance it has tbe apiiearauce of a Uttleiltered serpentine. Under tbe microeeope it is, however, .shown to consist predominantly of cai boiiiiti's in coarsely granular aggregates between which lies an intiuiate mixture of chloritic, serpentiuoid, and aeridtie libera. Grains of cbromite, trandncent with deep-brown color, do not appear to have been altered. At the same locality a large mass of tbe country rork (148 G.V.) is included in the quartz, and this sliowB a still farther reaching alteration. It is greenish gray and distinctly acbistose; remaining tllms and streaks of greenish serpentine or chlorite appear in a predominant gray, finely granular mass. I nderthe microscope tbe principal coustitueut is seen to be magiiesite in large

154 GOU)-QtTABTZ TBWB OP MSTAOA CITT AMD ORAM VALLEY.

Kraiiis ; there is a little chromitei and unity veiiileta of qnartz. Between the cartwnate gralos and extending into them lie wavy itarallel streaks

of a fjroeiiisli ininoral, in ])art clilorito, in part seriieiitiiic. A fi w giaiiia ot pyrite, bat almost no sericite, atre outed. Tliere are also ui intimate conneetton wi the serpentine fine-grained sfirfregateB of quartz. The analyses of this 8]>fciinen is recorded iiiidiT V in thf p. lit). It may be calculated as follows, under the supjKjsition tiiat all of the calcium and the larger portion of the magnesium are ]ireaeut M earhonatoB, and that there is aboat 26 per cent free eiliea pneoit:

I'rr rent.

Magnesium carVHmste .H4. 78

Calcium carbuonto ' 23

8rpmititie.liliNito,andaceaaorlM 31.00 i

loaoo I

The residue ut' seriientinis eti-., would thi-n live the tuUnwiug cumpo* itiou:

PeO 18.00

MgO 21.57

Ho I 9.M

I : I

This is evidently a niivtiiri' nf itiiucnils, ])n>]iably chiefly chlorite aod mrpentioe. As in the other analyses, the ferrous oxide is lu exooUy and it is doabtftil to which mineral it belongs. The cbromion in flie rock has not beeu determined. The fvee quartz in the analysis results partly from the small veins intersecting; tlie nwk, bnt some of it rejiresents without doubt the silica bberatcd by the conversion of the magnealan silieatee into magnesite.

BXAMPLB or ALTBBBD 8BDI1CSRTABT BOCKB.

The massive siliceous argillite the Federal Iahui, of which an analysis is appended on a preceding page, shows under the microscope ft very fine trraiued allotriomorihie, appi-eprate of quartz, feldspar, and brown mica, together with much pyrrhotite and some organic matter. Under themetasookatie influence of the vein solutions this is altered to a yellowi.'ih array sericite, ealeite, and residuary quartz; the ]>yrrhotite is changeil to pyrite. This alteration is, in a general way, well shown ou PI. Vll, fig. b, representing in natural size a piece of

Chemical Altekation.

vein qiini tz nd joining tli(> wall in tlie Federal Loan mine. Next to tlie wall llu re will ubberveil a lurgu iiiiuilK'r ut' HUiall uugular fragoieuts of thoroagbly altered rock of yellowish-gray color. This sone next to tlie wall reprcscuts the fine detritus aceunuilateil on the foot wall andcenieiited by <|iiarti!. In the main quart/, iiihkm are several fragments of euuntry rock in different dcgreeK of alteration. The sbar]> outlines of the fraents, especially of the one in tbe lower rigbt-hand corner, showtiiat ehanpe in torn or roiiiidin': of corners does not necesHarily the uietasuinatic in must uf the Iragments in also bown in all degrees a tendency toward replacement by arsenopyrite as a last .itep in the nietasoniatic ns well as an inclination of tbe pyrite to cryHlallixe around the fragments. The pieces of country rook, it is held, fell into the forming mass sinmltaneoasly w ith its To .some extent tliis bleaching uf tbe black argillite is ui.so shown on I'l. \"111, c The ndcro.Kcope shows this altered yellowish gnty ruck to consist of a muttled mu.ss of clear serieite flbem, between wbicb lie clouded maeaee of fine grained ealeiteand

some liMiroxenc ititiinite). Tbere are. further, ahiindftttt }r''!>'i"* ">f pyrite and some arsenopyrite; in some |*laee.H there are, witb tbe nnaller masses of pyrrbotite, very strongly suggesting an alteration of tlie latter into tbe former. Many veinleta of earbonatea an preaent, wliifli a nile coiitiini litllf pyrite.

An analysis uf au altered wall rock collected un the lump of the mine is recorded under lY in tbe tablei, p. 140. Tbe rock analysed is pjwXy with sjilintery fracture, contains many small vcms of carVumates, as well as much pyrite; small grains of pyrrhutite are occasionally visible. Tbe analysis, while ebaracteriatle of tbe metaaontatio rocks of tbe gold veins, does not indicate a derivation £rom an argillitev but of a basic rock rii li in titaninm aiMl magnesiam, such a.s one of the uumeruus dik&s eontaiueil at this leiuity in tbe prevailing rock.

The analysis may be calcalated as followa, on the sappoaitlon that theie is 7.75 per cent fte silica present:

Cali-i nm carboitsts. . . HagiMsinni mriMNWt* i-arbonat*

P.vrit<-

Tiuuiite..

Water bdowllOC.

9B.M

156 aOUHlUABTZ YVINB OP RBVADA CITT AHD ORABS VALLET.

In fhlB analysis thers is snongh carbon dkolde to form earbonatea

with all of the cahiuiii. inaffiicsiuni. and iron pn'sonf. The Bericita would, ou tbu above suppositiou, have the following conipoHitiou:

PI. VXIIf flg. 0, represents in nntiinil atxe a inicn from tho old Banner mine (77 N. 0.)i showing well tbe shattering uf the dark argil lite by a network of qnartz veins. Having been exposed to weathering, the carbonates containing iron have aawuned a color, whii h permits one to distitijiuiHli their (rMjnpiit aloiif the sides the veiuletSf in contact with the argillite, iuHteud being mixed irregolarly with tbe qnarts. Tbe arilllte does not appear much bleaebed, but is fllli'd by )iyrite crystals, while there is no pyrite in the quartz. In thin section this lining of the fragments by calcite is even more characteristic, while tbe aiyUlita ts seen to be more attend in places than wonid be expected. Sericite fibers have developed in it, and small miCKMCopio veinlets of calcite cut across it.

At the Osborne Hill mine the vein, lies in jjorphyritc breceni. with abundant fragmeuta of n sedimentary, brownish gray, tine (raitied ro( k. A 8pe< inien of the altered rock adjacent to the vein (8,{ (i. V ; lias li'lit gray color, is tntversed by many small quartz seams, and coiitaiua diary crystUs of pyrite. The thin section shows an original extremely fine frrained, clastic atruotnre, chietiy of quartz grains, 8troni,'ly recall iug the urgillite of Federal Loan; between the grains, and also in them, lie very fine felted aggregates of aericite Abort. The analyau eon- Arms the evidence that the rock Is derived from a siliceous argillitu. Tbe absence of carbonates in the altered rock is uutable. The analysiB No. VIII in tbe table, may be ealenlated as fbllowa, on the estimation of 00 per cent free silica:

quaru I 30.00

Sericit*

Calcite

Maftnesfto ,

Apatite

Titanite

Water below 110 C

.as

.:w I0U.37

umwRWl CHEMICAL ALTEKATION.

Aud the 8ericite would have tUe following

Aiijilysis III 8I10W8 tilt' composition of the ro< k from the foot wall of the Ural vein in the I'rovitUnice iiiiiie It is a dark-gray, titiegnined rock with black, shining, and carved planer of nchistoMity and containing many small but extremely sharp crystals of pyrite. Under the it is iliRVTciit from the crashed granodiorite the huiigiug wall ol ihe time vein, the original structure being that uf an allotriomorpbic, fine'graiiMd qnartz-fbldspar aggregate? this stmotare ia now partly veiled a development of sericitc, carbonates, and chlorite. Betiides these are many Hniall crystals of an opaque mineral which may be magnetite. The analysis sbows a great BimiJarity to II, which iH the crushed granodiorlte from the Menifleld voin. The origin nal material is, however very diftteent.

Gold Ahd Biltbb Oontxnts Op Vbs Ai.Tsbbd Wall Books.

As has been stated before, the wall rocks, replaced by carbonates, HCricite, hihI snlpltiiles, generally contain very little of tlio precious metals, even when adjoining rich ore sliMits. A number of altered rocks were tested by Mr. O. Whitehead, assayer of the mint, with generally negative results.

T

212 N C , Prov iiloiK-e mirn> ( Analvftm III)

G. m.

IfKi c. v . North Star mine; nar rich qosrts

aoM.

Nobs. None. None None. Tnm.

None

8iltr.

iVr etnU

oet I

None.

It is worthy of note that the silver predominates, while in the quarts the contrary is the rule.

Chapter Xi.

Vein 8Tbuctube Axd Pat Shoots. Structurb Op Thb Vbins.

The cliaractT of the flssaro detenniiu's, to a great extent, the strnctnre of the veiu. The Rimplet Ibriu of a Ussure a joint plane, 8ucb as 18 Been in regions of intense sbeetiug about the Lecomptou and Caiiiula Hill inineH or ia the seam belt of the Red Hill west of the Tily mint'. On some of tliese joints tliere is a narrow line of quartz, by u slij;ht bleak'hing of the rock on each side. Certain of these breake along the Joint planes may be more pronounced and extensive, or one larger lireak may be prodiicel instead of a series of smaller oneti. In such case there in UKually a more noticeable movement along the fault plane, and I he sliding of two irregular snrfaoes on each other more or less <-ontinuonH spaces, which were tilled witii <]uart/.. This is (he character of the Idaho- Maryland, the Monntaiueer, and the Ouiaha veins, for instance, and is veil illnetrated by PI. XI. The vein here consists simply of a filling of white quartz 2 to 3 feet wide between two pai allel surfaces. The regularity is nsnally not maintained over a large extent of the vein. It is extremely oomnxm to find local pinches, and sometimes the vein is foniid to closedown to a mere seam in wlioie levels, above and which ;ood ore is found. Again, in jthu cs the vein loses its regular character by reason of local fracturing antl lirccinating ol the hanging wall. A typical ooenrren< of this kind is shown on PL XII (see also detailed des< ri])tioiis. Idaho vein, p.220). To this ttrst rehttively simple type many veins in the district belong.

Another class of veins, to which the the North Star, and nniny others belong, presents a somewhat inoi e <-ouiplieated structure. In tliem the simjde clean break is re|>laced liy a comiMnuiil mie. in which two or more distinct fractures have bcH'ii i'ornicd at a distance of afw feet; between these lies more or less cmsbed and breoeiated rock. Qiiai tz-filled fissures lie alfiig the liaiiL'int: vaU or along the foot wall, or aluug any minor break in the rock between the walls. The letter may more or less distinctly assnme the character of a breccia cemented by quartz. It is usual, however, to And the main qnarts vehi close to the hanging wall. The ro< k between the walls is always most altered by metasomath; proce.sse8. The little veins and seams, sonictiuies. lui on XIII, forming a network in it, are iredonrinitIy composed of calcite. This stmctore is illnstrated by Pis. XIII, XIY, and XV. See

I

Vein Stkuctlke And I&#x27;Ay Shoots.

also tig. 18, rittsburg vein, p. The liaugiug wall is generally more distinct than the foot walL

In tiiH exiuiiple.s iiietittDtied thus &r, the eviileiict> of extentiive movement nioiifr the viMii is less pronoiinred, the brett iatetl structures indicatitig a 8uddeu short breiik rather than a long cuu tin uud grinding of tbe walls against acti other. Sohiatoae atmctare, dne to the latter ("onditiou, occurs ill ]>l;ices — tor instance, aloii both walls in the bhiho- Maryland and the North 8tar, but only iu the Ti al aud Memdeld veins does it becomes prominent. In these the quart/, where the vein is simple, is adjoined by several feet of aoiiistoee rocks, by the piessnre and movenient aloiifr tlie tissnrc; where the vein is eomsmaller streaks aud seams ut quart/, are distributed through this aehlst, which may attain a width of 20 feet or more.

The width of tlie |iiart/ \'fiii may in some cases attain several feet. On the Merriliehi vein a width of aud lU feet of solid quarts has been obeerved, and in the Ural vein, in the Nevada Oity mine, one smaller (Mc IkxIv reached IL' feet. Ordinarily - to ."5 feet is the width of the Merriheld and I'rul veins. The other veins in the Nevatlu City district will not avnmge 2 feet in width. With a fiBw exceptions the veins in the linnner Hill district are narrow, averaging hardly more than 18 inches. The Grass Valley veins are narrow, exeepting the Idaho- Maryland, (iold Point, and a few more, and scarcely average IS inches in width. .Many veins, such as llill and lorambagua. have paid well w ith an nveratre width of inclics, or even less. Seams with only an inch or two of quart; will sometimes cout4UU an extraordinary amount of gold.

In flic coinitarati\ ely soft black slates of tlu MaiipoNa rnnnation, along the Mother lode, a vein structure frequently appciirs, which, though not occnrriug in the region described, may be mentioned for comparison. The vein lies alou;; the contact of black slate and diaba, separated by a distinct, aud often polished, hanging wall of the latter. There is rarely a continuous and well-delined vein, but the bhick slate is ornshed, sometimes over a width of 20 feet, or even more, and Stringers of qnartz it in all directions, in the manner shown on PI. XVI, from a photiigraph by .Mr. N. W. Kmmens. Again, the pay is contained in the qnarts, bnt it is, of course, necessary to mine the whole width of the strin'er zone, wliicli tlitis Ciiriiishes lai masses of a lowgrade ore. The plate shows, iu addition, a curve of thepriuciimi mass of quartz, which may be dne to movement snbeeqoent to deposition.

The Pay Shoots. : I &#x27;.N Krai. Fe A 1 I &quot; U I .S.

The rich qnartz may occur iu entirely irregular patches aud areas on the plane of the vein. It is much more common, however, to find it oeonrring in more or less regular bmlies, usually referred to as . aboota. Extremely rich masses of small extent and irreguhur are

160 GOLD-QUAKT3S VBIMS OF NEVADA CITt AMD 0RA88 VALLBT.

calleil 'poeketa," or wUeii they have a regular, loug-drawii furiii, cliimiuqra.'' Poeketo with local accumulatioii of coarse free j;oId oftea occur in tlie ]>!iy slioots of the Cimns N'iillcy 'nines; flu* Peahwiy iiiul also the Gold Uill mines in Gnws Valley, the iSnealh and Clay and the Mohawk near Nevadft City are examples of sneh pocket veios. The quartz between the pookets nay be almost harreD or it may contain a fiiir-grade ore.

In most uf the voiim the development of quartz is not eonliued to the ore shoots. In otlwr word, the vein preserve its goiienil character a large area, but only in jiart nf it — tin-on* slioot — (loo-< tlu <|iiartz coutiiin enough gold to be extracted an ore. in another and smaller class of vdns, represented by the Nevada Oity, the Omaha, the Pittsburg, and other;, all quartz occurring in the vein is good ore, and outside uf the ore shoots the vein cloKea down to a seam. The quentioo what grade of quartz is regartled ore of course influences the extent of the shoota. In the districts here everj thing above f6 ton, the average cost of dc<']) mining and luilling, inchuled 18 OM although in most mines thi tenor is considerably cxt;eeded.

FOBK OF THB BHpO'ltt.

A few characterldtio ore shoots an-shown on Pis. XVII and XVIII, and others will be found in the detailed descriptions. In general, the has au elongated shaiH*, and forms an angle with the liorizoutal plane, which geoerally dilliMrs, though usually not greatly, frmn tlie dip of the vein. In other words, tlie shoot iisnully pitches at a Rtee|) angle on the plane of the vein. The following law to govern the general direction : The tkeot witty at a rmte, pUeh to the left of an obtervar standing on the apex ef the vein and looking down in ike direction of the dip.'

In a number of veins there is, to be sore, no great regularity, or the ore shoot will often be found to dip at the same angle as the vein, bat

the number of instances in which the rule is applicable renders it indubitable that this occurrence of the ore is the result of certain conditions as yet nut fully understood. This law holds good in a great many mining districts of the (>old Helt outside of these here described, and it is certainly worthy of close scrutiny. Fay shoots dipping in opposite direction from tjiat stated above are said to occur on the Gold Flat vein, the Slate Ledge vein, ami the Little Diamond vein.

No rcliitifin coiihl hicstablislied between the direction of the ]ay shoots and the direction of the striatiou on the walls. According to the so-called Glaytons law, they should coincide.

Pay shoots may cross from one formation into another without change. As examples may be cited Providence mine, Merrilleld vein, in the Nevada City district; Union vein, Banner Hill district; Empire vein

WliDr tbia lav haa Ih'ih well known hy tbominara for anuijr jean, jil it liaa mil btn-n allatinrUy

iiiai. .nH-f<.rr. I ii BaaD' IHiwiavr it to appUtd tte DMtk-Hd-MiiUi Tttea |p. SutMMBi '

b>' 1'. U. Uulfel.

d by

U. M. QlOtCXIKAL ll*VtV

BUNKER HILL VEIN, AMACX3R COUNTY. CALIFORNIA: STORES ABOVE 300 FOOT LEVEL, SHOWING VeiN SPLIT UP INTO SEAMS IN SUkCK, CRUSHED CLAV-SLATE,

Thk Pay Shoots.

niid (Jraiiite Hill Vfin, (Jrass Vallf v district. The apex of most of tlie large pay shoots diacovereil very iialiuaily crops on the surface, but this is not an invariable rale. The apex tlie Earelia-Idaho sboot, tot instance, was foniul at a of about lOO U-ct ; tin-of the main ore shoot of W. V. 0. 1). waa not found till a depth of aeveral hundred feet was reached; neither did the rich shoot on the Ural vein in the I'rovidence on the surface. The |NMMibillty of finding a new ort' shoot at any (h'ptii twist he coiicrdt'il.

While the largest ore sliooUi may he tiom several hundred up tu2,0UU ftet wide and np to 3,000 feet long, there are many shoots on tlie smaller veins which have a much less width and length. These smaller shoots sometimes go down to great depth, but are in general less to be depended on fbr permaneaee in depth than wider ore bodies. Even the small chimneys and iMu kets in the seam belt of Ked Hill are stated to follow the law stated

The >'urth 8tar workings (HI. Will) form an e.vcelleut example of a Iwrge ore shoot followiugr the sania law. In this ease the main shoot is composed of a number nf smaller ore Ixnlic-* with similar trend, separated by spaces in which the veiu has closed down to a seam. The Boreika-Idahn ore shoot (fig. 27, p. 229) is nniqne in its long extent and Hatdi)); this is also probably tlie most uniform slioof in the district, ootttainiug relatively few bai*ru places or pioclies aud having a kuowu langrth of over 3,000 fhet. No relation of the ore shoots to the cross flames eould be found. Indeed, the latter are generally later than the ore fissnres and do not carry (piartz. IiitersfM-tion of veins— a pheuomeutm nut very olten ohservinl — will sometimes, but not always piodttoe richer ore bodies.

I'KRMANKNCi; IN HKPTIl.

This question is oueuf the highest iuiiKU tance, bringing; up the whole fhtnre of the indnstty of gold mining.

It is certain that the experience with many of the snutller of ore is that they give out or jiincli at varying depth.' Others, again, have continued to the greatest tlepth at which the e.xploitatiun of the mines has been carried on. Similar relations prevail in regard to the large ore shoots. While some have been found to <'ease in depth — the Sierra Buttes mine, in Sierra County, being a well-authenticated example— others oontinne to the deepest levels as strong aa or atconger than in Ibe upper {tart ut the mine, the Kennedy mine, in Amador County, being an example of the latter chips.

The frequent local irregulariticMS of must shoots make it very dillioult to affirm, witiiont extensive explorations, that the end of any certain ore body lias been reached. Owing to the habit of immediately dis tributiiig all of the profit as <lividt'ndK, reserve funds for exploratory

Tliia diBcuMluii rebn only t'> ttf i'tt' tliv row' oxUUlinti, It U wvll known tbt Ui* mm tlw water lerelan> fr'iiu . .iii.r. ..r tu. ui . niii-,'nirailoii. richer thu tboM Mt altMWd, M taiyvvmrlahiminl nmr gi-nrrally Inbvlitw tJi* watrr level.

162 Oold-Quartz Veihb Of Nevada City And 08A88 Tallbt.

wurk ure selduui aivuilable, uud a iocul iuipoverisbiueut iu a level liaa ofteo beeD mfflcient to close a food miM. Bzp4eace with the large

shoots is still insiitlicieiit for safe generali/.ation.

The ore shoot of the North Star extends for a distance of about :i,5lK) feet iu depth, measured along the plane of the vein. Vllieu apitroacliing the sedimentary area to the vest, it was cat off or divided into stringers. Still, the explorations are scarcely extensive enough to affirm that its end has been reached; its coutiuuatiou be found, or a parallel Bboot may be found in dep. In the ease of the large Empire shoot a oompUcatiou 1ia.s arisen, due to a split of the main vein, reducing the tenor of the ore by dividing it on three veins. The Eureka- Idaho shoot has held its own remarlcably well and nniformly over a distance of over 5,<Hiu feet, though the richest part of it wsui probably found in the Kureka and the western part of the Idaho ground.

High-grtulo ore is now mined iu the Maryland mine on the same shoot at a vertical depth of 1,600 ftet, and a small ore shoot was found near the bottom of thi' Idalio shaft at a di ith of feet. As gold (iuartz veins of fair grade occur near the summit of Banner Uill, at au elevation of 3,800 fbet above the sea, m 3,600 ftet above the bottom of (he Idaho shaft, we have in this district within short distance a vertical interval )f 3,500 feet within which there is no evidence of any gradual change iu the character or quality of the ore. Again, in the vicinity of WMhlngton, levada Oonn, excellent qnarfcs is mined 600 Itoet below the river level, in the Eagle Rird mine, and on the ridges north of the river 2,000 feet aliove the river level. Iu thut distance there are no distinct diffiBrenees in the quality of the ore.

Maoy mall veins carry only one ore slioot, but in the larger fissures then* are generally several of them. Tlicre is a strong that iu such veins thorough exploration laterally or in depth will develop new bodies of ore if llie one on whieib explaitatioa has been earned on is fdiitHl fo pim h out. The question will naturally arise as to wheflier, with iucreal depth and cost of mining, it will be a good venture to carry on the neoessaiy dead work. This will have to be decided by the record of the mine and the character of the fissure.

It is generally eon<!eded now that fissures are. comparatively speaking, surface phenomena, and that below a certain depth, where plasticity and flow of rocks under pressure come into play, open apaeea can not exist. This limit Professor Heim, for instance, jdaccs at feet, while I'professor Van llise, basing Ids consideration on the strength of rocks, arrives at 33,000 fSeet as the maximum limit hard rocks in which fissures can exist. Even the lowest of these estimates far exceeds the depth of practicable mining. But it is not likely that all fissures continue until that limit. On a small scale the discontinuance of Assures may be observed in extensive sheeted outcrops. It is also au incontestable foot that many small veins' close np in depth, while

ThMa omn Umum, Unogh Mt to Sapife. My aMUgp tem bM MiwrtMt to th tlMiwJiwtiimiiM— — iwmiiitlM thi wilhtlwlMiiriiMhillfc

U. QEOLOOWAt. lUUVtv

The Pat Shoots.

others coiitiiuuluichiiii'if*!. In foiisidcriiit the ixTiiniiiPiicy of a giveu vein, its general cliaructer luutit be takeu into cousideratioo. CoDtiniioiu iren-deflned onteropB mid wide bodies of quartz are in general good indications of the inalntenanco in deptb, as is also any evi* dcnceof faulting and movement. Some quite exteusivo veins, tboQgb, have relatively abort uuterops. Thus, the Eureka- Idaho pr:ictically shows cropptnga only for a distance ot 2,000 feet, Imt witliin that distance they are very prominent. Those of the Star are letiS than 2,000 feet long. From the developments to the east along the Omaha system it is pretty certain that the vein does not eontinne hr across in that direction. A finsiire which can be definitely ])roved to extend only a short distauce will in all probability bo found to be eorrespondingly limited in depth. In regard to permaiiency of the vein in depth, the Fral antl Merritield, along which eztanflivn faulting has taken jilace, stand tirst in the district,';.

In scrutinizing the scout statistic-sot the toiisaud value, of the* Grass Valley district, it can not be denied that they show on the a distinct decrease. There is also a distinct ilccreaHe in the average value of the ore. It not safe, however, to draw too farreaching condttsions from these data, beeanae there are many iiietora involved: The cost of treatment and mining has deerea-ned greatly by reason of the modem methods introduced, and more low grade ores are now milled than formerly; uor are there any rich urfai orei left to swtXl the grade.

Leaving the difficult question of" dct ]) initiing out of consideration, there are, however, in both districts a large number uf veius which have been only slightly developed, bnt which with improved methods may be converted into paying mines. The developmoit of these will probably maintain the of the district for many years in tlie iUturei even if no new ore bmlies are discovered iu the old mines.

It can be oonfldently stated that there no gradual dimlnntlon of the t*Mior of the ore iti the slioots hclow the zone of surface decompoiiitiou. Within the same shoot there may be many and great varia* thms of llie tenor, bnt there is certainly no gradual decrease of it from the snrftoe down. This important fact has ]iccn ]>rcvionsly stated by those conversant with the veins, such as rror( Silliinan and Mr. J. A. Phillips. The statements to the contrary, for by Mr. Law or Mr. Bcjyer (see literature in Chapter I, pp. 10-17), are doe to imperfect aoqnalntanoe with the (hets and generalisation frwa insnffldent premises.

0Bo8B-0Dttuio.

As a means of finding new and parallel veins, cross-ontting is frequently advisable, espe ially in partis where strong shcctinj,' of the rocks prevails. In the larger part of these districts, however, a series of parallel, distinct veins appear instead of the These veins are nearly always tnu'eable on the ground, anl in such cases croasenttiug has rarely developed veins not known already on the sorfiuMb

Ohapter Xit.

TIIK KISSl-IlK SVSTKM8.

Thai the veius ure practicuUy iudcpeudeut of the geological structure and that the strike and dip vaiy greatly are fiMita that have already

\yeen ciiipliasi/ed. TTowevei. oortaiii systems with definite relatfolM btwtii one another may be easily reooguized.

THB VBIN8 WITH A OBNBRAL EA8T-WBST tTRIKB.

Many of the most important (k'|Kisits nf district nie found on ▼eins having a general eaat-west strike, which may be grouped in a number of snbeiaiaes:

The Willoir VaUgrOMp. — This coni]>riseM the veins with moderate northerly or, more rarely, noutlierly dip (as the Federal Ian ), occurring along Deer Creek, iu the Banner Hill district, from the Texas mine to the Oonstitatioa. The strike generally a little north of east. The central eastern part of this system is intimately connwte*! with an exteutiive system of sheeting crossing the grunodiorite contact. 2nowhere, indeed, ran the close nonneetion of the veins with the eheeting of the 'pantry rock be better demonstrated, the veins forming the most ]iromineut of the joint danes. The fticts noted in the detailed descriptions of the Federal Loan and the Never Sweat mines indicate the Intimate relation and origin of the veins north and those dipjiin}? south. It will be suitable to dcsiinate of veins with the same strike but symmetrically oppijsite dip as conjugated systems.'

A line of veins with east west strike and moderate to tiat southerly dip extends from the Maytluwer and Beckman to the Mohigan, south of the granite conttict and evidently belongs to this group.

Tkg North Star group. — The strike in tliis jjronp, which is developed only in the vicinity of the North Star mine, is generally WNW., and the dip moderately to extremely Hat either north or south. The extremely intimate eonneetion between the veins of these ootOoffated systems is iiLram made clear by the in the New Kocky Bar (PI. .\XI1), where two veiuti, one dipping north and the otbei' sontb, join in a curved arch filled with qaartx.

The St. fMUw group. — Re|<resented chietiy on the Banner Hill sheet the St. Louis. I?i>.' T'.liie. ami other veins, this is distinguished by a .strike about to that of the Willow Valley vein, that is,

Oigiiizea by

Thk Fissure 8Yktem8.

e:i8t we8t or VVSW.-ENK. Tlie dip is, however, very steep, ajiproaohing aud nnerally a little toward the north ; the vciiis are often wide, bat jrenerally of low grade. In the iiraiia Valley distrtot and in the viriiiity of the Pittsburg iiiino iiiiil at otlier pliu-es in tlie Nevutlii City district there occurs a series of joint phones and tlsHures, rarely filleil with quart/., which cnt and sometimes fault the veins beloii;:iug to other systems. The dip is steep, to the north or aoQtb, and the Btrike in luo-it t-uses ENE. It is jfrobable tliat the.se " oroKsiiigs," they are locally called, belong to the St. Louiit group. That they are Btill open Annres ia indicated by the ease with which water eirealatea on tlu'in; they an*, in fart, the principal subfcrraTH'iui watercourses, and in the vicinity where tliey jHrnrail the niiu.s will drain all the smaner ones in the neighborhood.

The MvhhOrleaHH group. — Tliis ilivision is cliarai terized by a HtriUe varying between cast went and WNW.-KSI".. ai]<l ;i stjM*p, generally southerly, dip. The latter is, however, itouietiuieM also at steep anglea to the north, and, indeed, the Bnrelra vein is said toetiange from a southerly to a iiortherly dip in its western extension. The veins belonging to this gi-uup are strong, wide, aud well The Idaho, Orleans, Goe, OoM Point, and Imperial (on Deer Creek, west of the limits of the slieetsi are illustrations. In which gronj) the Spring Dill, Alpha, and Kentucky sliouid be cohuichI is tlonbtfni. Toward the east the veins belonging to this group acquire a more <lucided northwesterly strike, In this group again, as in tiie others, there are indications of two ooqjngaled systems with dips in symmetricly opposite directions.

THE VEINS WITH A OBNBItAI. NORTH-SOUTH STRIKE.

Ti this cUwM the majority of the veins belong, both in the Nevada

OMyand the (irass Valley di.strict. While the strike may be subje<-t to vftrlHtions extending from NNW. to NNE., there <loeK not mem to be any reason for separating thexc veins into more than two

The Providence group.— Wp, medium to flat to the cost. These veins are lepresented in the naitner Hill di.strict by the Ilanner Hill system, as well as by the Buckeye, (iraut, Enterprise, aud others. In the Nevada Oity district they are extensively represented by many smaller veins and by the imixtrtant system of six or seven veins, radiating ft"om a point neair Town Talk toward NNW. and NNE. and then agatu all bending toward NNW. The Tral vein makes the most sudden bend, changing to a direction ]ractically itarallel to that of the Orleans- Idaho system. Tlie I'ral aiul Merrifleld veins are anion;,' the most important iu the district, and extensive faulting has without doubt ot;cnrred on them.

In the (!rass Valley district veins dipping east at Hal angles are found on Cold Hill, MaHsachuHetts Hill, aud along the foot of Hill. They are generally narrow and often very rich. Sheeting parallel to this gxonp is noted along Wolf Greek at the Larimer mine.

166 Gold-Quabtz Veins Of Nevada City And Grass Valley.

The Omaha-Empirf fjrnuj). — Dip, iiu'dinm t4> flat to the woat. This group is also of great imiiortaDve. la tbe Bauuer Uill district it fa represented by tb Deadwood, Marohle, and Canada Hill veins, at the latter plac accompanied by extensive sliaatingnf th6 gnnodiorite: in tlie Xfvada City district only a few larger veins, anrh as the Siieatli & Clay ami Llie Mohawk, dip to the west, but in tbe seam belt of Ked Hill, west of tbe Kevada Oity mine, a great number of seams and narrow veins dip in that direction. Tlic direction been, however, changed so much to the northwest, following tbe great bend of the Ural vein, that the Identifloatlon with the north-sovIA dass of veins becomes donbtfnl. In tbe Grass Valley district this group is abundantly represented by tlje Dromedary vein, continued south wanl by the Oinuiia system, and by the great Empire-Osborne Hill system of linked veins, in which the general direction has banged to some degrees west of

nortli. Extensive shcetinfr parallel to this {n*oapof TOinS Is shown in the northwestern part of Grass \'alley (Fl. III).

Oonsidered togetlier, these two gronps may again be regarded as eonjngated systems of fVaetures. Tin* nt certain mines, such as the Pennsylvania and W. Y, t). D., show the very intimate existing between the two groups and their conteuiponuieous origin, tJieqaarte veins of one gnmpsouietimee iUling back on flssnno belonging to the other.

In eneh of the ditfereut groups of the east-we.st veins, as well as in the north-sonth veins, there are tboa two conjugated and apparently eontemporaneoos systems with approxinuitely similar dip in opposite direetions.

Intbrsbction. Paultino. And Rblativb Aob.

Intert'ction and faulting; are not of frequent <iccnrreuce, and the opportunities for examining; such phenomena from personal inspection are not abundant during one short season of investigation. The following facte are gathered from the detailed i ijitions:

Veins (it tlie Wiilow VaHey rronp fault the iieadwood vein, which dips to the west, producing a reversed faulL

The Big Bine eots through the Lone Star vein, dipping west. The St. Louis vein faults the Canada Hill, dippintr west, .'vnd tlie fault is Again a reversed one. Several east-west veins about pantUel to the St. Lonis fenit the Floyd, dipping east, and the Beekman, dipping sooth. movement is apparently a relative down-throw of the south side, diagonally inclined toward the east.

The Nevada County and the Mountaineer veins iu-e faolted by eastwest veins. The Pittabnrg and the Gold Flat veins are repeatedly eat and somewhat by iM'rin-ndiouiar east-west seaoiS, resulting in a relative downthrow of the north side.

In the Grass Valley district the barren erosa-senna with steep dip and BSnS. strike frequently fiult the veins of the Empire and Korth

The Fissure Systems.

Star prnupa a little, the invein'iit being gonorally in tinimtnrBof a reversed fault. A bending of tlie faulted vein is very Irequeut.

The fiuilts MeaometimeB efTeeted by Mingle fiiult planes, but itk more to tind several itarallfl plitnes a short distance apart, on which gradnally ilecreasing difl'erential movement lius taken plaoe. Summing up the evidence, the obtitined are: That the north-south eontmnporaneons oojngatcd Rystems are the oldest veins:

That the veins ot the iSt. Louis group are the most receut, and that the Grass Valley cmasings," though not as a rule filled with quartz, belong to this group;

That the coins of tin- Willow Valley group are more recent than the north-south veins, but older than the St. Louis veins;

That the North Star gnmp ia probably contemporaneona with the Willow Valley <;roni>;

That there is uu direct evidence of the relative age of the Orleans- Idaho system, bnt that ft is probably of the same age as the north* south veins;

Tliat reverse (overthrust) fauits, with a relative upward movement of the hanging wall, are prevalent. In the iMerrifleld and Ural veins the throw measured along the hade of the faolt probably exceeds 1,000 feet, while in all other known cases the ilisphicement is relatively small possibly excepting the Idaho-Maryland vein.

Relation Op Thb Vbin 8Y8Tbm8 To Obolooical Structurb.

Ciinsidi in detail, no connection can be said to exist between the distribution of the veins and vein systems and the geological structure. Veins of the different systems ooenr In practically all the diverse rocks and croesall principal ooataets without being'influenced by them. They do not, as a rule, any contacts except where snbseqnent faulting has the phine of the vein the contact plane. From this Statement shonkl, however, be esieeptod certain veins in serpentine,

such a-s the Kentucky and in ]):irt also tlie Eureka Idaho, which ShOW an Incliuatiou to follow the line of diabase dikes in the lirst>-used rook. The veins do not, except locally, follow the sehistosity in strike, and

ajiparently never in dip. The diflerent dejjret: of resistance of rocks to det'orniation of course intluencea the lissures to some extent, but considering the great diversity of rock types this inliuence must be charaeterised as slight.

The fissnres are more apt to be straifjht and clear cut in hard, evengrained rocks, such as diabase and granuiliorite, bciug spiiutery aud irrsufnlar and easily breaking up into brecoiated zones in arglllite. Fissures in serpentine rarely continue unbroken for a long distance; in fact, to enter seriientine seems fatal to the coutinuattou of most veins.

It might be said in a general way that the veius of the Willow Valley group are narrow and contain rich ore, mnoh snlphorets, and a

168 tiOLD-gUAKTZ VEINS OF NEVADA CITY AND GRASS VALLEY.

confiidprablc pen pi if ape of silver, hut ferfuin north sonfli veins in tlie 8ame district have tlie tMime characteristicB. The Idabo-UrleaDB group magr be Gliaotrixd in general u heavy veins with bat little snlphnrete end httle eilver. On the wlurte,*tiie niles whieii might be addaeed

Nor can any distinct mtlueuceof the ooiiutry rock be said to exist. Yeios ocear in granodiorite, diorite, gabbni, iiyroxenite, and serpentine; in dlabaw*, porpliyritic diahasc. iviul porpliyrites; in ainphilxtlitic. chloride and micaceous schistK; in slate, ttaudtitoue, Hilioeous argUlite, and oontnet breeoiae. In aeratinizing elosely tbe data in the detailed description it is found tlnit the nietnsutniitic prmjses have been prae* tically identical in all tliise rocks, ami that the character of tlic lillinfr — that 18, the principal ore — varies greatly, but is not coustaut for the same rook; it even varies in diiSarent parte of the same vein in the same rock. Veins in {rraii'xi'orite and arfrillite often carry much snlphuretM and silver, veins in diabase little of these substances, aud of the (inner ohieHy and galena. But these tentative rules have so many exceptiniitliat their value becomes extremely problematical.

On (he other hand, the inllnence of Imulily is strongly pronounced. The Willow VuUey and Canada iliil veins form one the City veins another, the Providenoe-Mountaineer vmns still another. The sontheni einl of the Oslwrne Ilill system is fltarficteri/eil by arseilOpyrite, as are the Forest Spring veins, iu greatly litteriug rocks.

Leaving the details and looking at the ooenrrenee of the gold veins at Nevada City and (n ass \'al1ey, together with those of the surrounding country, the great (utnceutratiouof deposits iu the district described is the lirst striking fact.

To the west there extends down to the foothills vast areas of granodiorite. diorite.s, and porphyrites, in which only scattered quartz veins occur. To the south the almost barren augitc-porphyrites reach down to Anbnm. Toward the north stretches the granodiorite massif of Hevada City-San .luan. containing many placer deposits, but few qnarfci veins. Eastward, finally, are the sedimentary clay-slates of the Calaveras formation, on which lie many placer deposits and which contain many small, scattered veins, but no important vein systems nntU the vicinity of Washington. miles east, is reached.

lietween these relatively barren areas and the crowd&d fissure systems of Nevada Gity and Grass Valley, filled with rich gold ores, the contrast is very strong. Considering the veins of lianner Hill and the Nevada City district as a whole, it can not fail to strike any observer that, while octuirring in any of the several rCcks of Hie vkinity, they are chiefly grouped idong the aemidrenlar oontaetof graoodiorite with tlie older rocks.

To the south of this zone is a comparatively barren belt until the Grass Valley district is reached. Here again the veins show some relation to the smaller massif of granodiorttei oocurriBg ou both sidesof it and in it along its whole extent.

imiiwui.l

THE FUBUBB BTMTBMa

ORtOIM OF THB FtSBUttB BYSYBMS.

The first point emphasized by tke 8tndy of the vHna te flie pnictioal fdentilgr of the joints and hvvt with the vdn flssares, the only differcnoe

being one of degrtH* uf (lislitcatioii. sccniid is tliat scliistoHity of the rocks adjoining tliu may homo exUnt by the same forem wbieh produced tbe veins and jutnts. A third is the f;n t tliiit ( in li ;rt "iip *'f veins cnotsins tv() sub fjroups, wliicli, with the same Htiikf. dip in opposite and symmetrical directions, the two sabgronps being de!<igiiated eonjvffnted ftactares.

The explanation 8 of tbe joints, fissures, and (Kcuriiomilly aooompanyintr schistose strm-turo appear to be furnished by certain experiments by Daubrcc' and by the mattiematical deductions of Becker/

It is plain that the formation of Joints and fissures and tbe movement proiluced on them are due to mechanical causes. Tensile stresses — contraction and dilation — can not, as shown by Becker, explain these phenomena, for they result in the of carved and Inoken, and not extensive jilane, partings; the fissures and joints would he gaping and there could be no slickensides on the parted sui'faoee.

Torsional stress can, according to the well-known experiments of Danbc produce two main sets of fractures approximately at right angles to each otlier, and usually at nearly to the axis torsion, the minor fractures otleu showing divergent directions. This explanation has been proposed for flssore systems— for fostsnee, tliose on which the metalliferous veins of the Hart/ are found. oloRcr examination show.s, however, that the flssures produced by tbe ex{)erinients are nearly always carved and warped surfaces, and not approximate planes, as are the tissnreh here under consideration.

Becker ' considers the experiments nu the torsiun ot ;.'lass equivalent to the application of a system of tensions [MMuliarly distributed, and that the flssnres prndnced in any mass phystcully resembling glass will exhibit the petuliarities of tensional fkactores, together with some marked characteristics of their own.

This theory rejected for the present case, the only one remaining is that of direct iircssure, according to which the joints and fissures are by shcariufr stu-ss. Tliis, indeed, appears to explain all the facts observed, and especially tbe frequency of overthrust movements or reversed ihnlts. In Danbre's beantiftal experiment ' on a mass of beeswax and n sin two coniu;:ated systems of joints and tissures were formed, making an angle of about with the line of ]>ressure, and similar results have been ohtaiiMd testing cubes of building stones. These conjugated systems, which are approximately at ripht apples to each otlier, reprduee very closely the north and south v<'ins of I lie districts here considered, with the

' ftlllllna dj nlllitiilili-i llr i.louis iijM rirililitlilr, p. '.ilfl-

Kiuili? ]imioirriiMHi Htruiii, ('U-- : UiiII.'m''i1 S-m' Am . Vol, ihi ., i:..

liiTKionml Ihrory uf >>tula: Tnuis. Aiu. lunt. Miu. Kd(., >Vliruur.\ . I8IM.

170 GOLD-giTARTZ VEIN'S OV NEVADA CITY AND ORASS VALLEY.

exueptiou that the lateral augle between the planes dipping east and tbom flippiiiK west in gfimniny mmewbat leaa tbaa W*. The eaatwetit flssnre systeuis iiior(> ineguhir, thu angles between the two sets of phities varying' t'loiii 20 n]> to nearly IMP, and ara at least in part, later thiiu the I'oniter Rystmn.

It tbuB most probable that the flssare sjrstems have been prodoced by ft ncceBsion of compreAsivc stresses applied in diSbrent direction% ehiy from east to west and from north to south.

In Hie stndy of this question the fhet shonid be borne in mind that not only vertical but to some extent aisti liorixontal displafeiiu'iits have occurrwl, as indicated by tlie ottt'ii iiicliiuMi direction of the sd iatioiis on the wall. The scbiHtose structure ufteu m'cuinpanyiiit; the veins appears, in oonfbrmiiy with Beeko: view, dne to relative tangential movement in the same diteerion as the flssnre, bat not reaching the limit of cohesion of the rouks.

Tbmpbraturb In Thb Minbs.

But few oi the mines of Nevada City and Grass Valley have reached a vertieal deplli of ovor l.(KMI feet, and thi' temperature of the air in the upper workings ordinarily ranges truui 33-' to (iO F. The Idaho- Maryland has at present attained greater depth than any other, and it seemed of some interest to obtain data from it as to the increase of temperature in the lower levels, even if the methods adopted were crude by necessity. A 2-lbot thermometer was procured from Mr. A. LietS| of San Francisco, and by him carefully with a standard. The graduation was in Fahrenheit. The iustrunient was inserUnl in bore-holes 2 to 3 feet deep, the opening carefully stopped up. with the neck of the thermometer protruding, so that it could be read by drawing it out a few inches. Tiie thermometer was allowed to remain till a constant was registered, usually about lialf an hour. The tests were made Jnne 14, 1804. A bore-hole was first made in the dry n tunnel, L'-'O feet from the montli and about .'W feet below the ooUsr of tlio shaft. The hole was 3 feet deep and in gabbro, the rock being very damp. Temperature in drift, 4-57° F.s-|-14.So O. Temiterature in bore hole, F.=+11.90C.

Tlie next observations were taken in the face of the drift on the fif teeth level, l,.*2.°t feet vertically below tlie drain tunnel. The point attained in the mine is 2,151 ibet below the drain tunnel, or 2181 feet below the collar of the shafti bnt no levels below 1,000 feet are now accessible.

A damp bore-hole on level lo gave the temperature of -1-660 p, or -I- 18.9° C. The water on this level had a temperature of i-62o F., or

Further observations were made in the stole lU feet above level 10, er 1,483 feet below the drain tnnneL A wet bore-hole in quarts gave tbe same reeolts aa 40 feet below, or -f 18,0o O. A dry bore-bole in

quartz tr:t\ a little biglier losiilt, 4-671 v., or +10,6" C. Tlio air in tlie stojK's had a temperuturt' of to 7o 1'.. or about +L'0- C.

Taking the (liiiup bore-boleji iii tUu druiii tuuiicl and on the tifteeuth hmi tu oompariMD* we Iwve an inereaae of 12o F., or 7° G., in depth of 1,523 feet. Supposing,' it to be iinifonu. this is iMinivah'iif an increase of ¥. per iUO fet, or C. per lOO meters, in other words, it is eqnfvatent to an increase of 1® F. per 122 ftet, or G. per 66 meters. Thi8 i.s probably the BMWt nearly correct value for the increment. Taking, iiowever, the difference between the dry borehole in the stojte and tlie damp one in tbo drain tnnnel, a difference of 13.75° F. in M83 flat, or of 7.7° C. in 45:! meters, is obtained. This corresponds to an iiicn aso of O.O.'l 1" im t KfO f''t, or of 1.7 jwr 100 meters. In otiivr words, it i8 e()uivaienl to un increment if 1° F. in 107 feet, or C. in 59 meters.

In disonssiiij; these results it should first bft stat4'd tliat the tcnijierature of 53.5° F. of the rock obUiined in the drain tunnel, 30 feet below the surface, i.s apparently considerably different from the mean annual temperature of the air. There axe no temperatitre data available from dress Valley so far m I know, but the rM'ords from Colfax. Cal.. 14 miles away and at nearly the same elevation, viz. 2,500 feet, cover a number of years aad give a result of nearly SO F. An average annoal temperature of F. is not until at an t'l( atinn of about 4,000 feet. It is further clearly apparent that the increment observed is very small compared with the valnes nsnally obtained. Evmi assam> ing the larger increment of about 1- F. ])er 107 ftet, the temperature would only 1m> !H at a dcptii of feet.

Prufcssur i'restwich' give.>4 the mean increment for coal uuues as F. per 49.5 ftet; for other mines, per 43.2 feet, and artesian wells, per feet. Diflcrent localities show, however, 'n-atly results. Professor llaliock found m the well at Wheeling, W. Va.," 4,000 itet deep, an increase of F. for 80 to 90 ftet in the upper part of the. well, and of 60 fn'ct in the lower part. JMr. Alexander Aga.ssiz' fuuntl recently in the Calumet and Ilecia copper mine, Michigan. 4,700 feet deep, an average increase of 1- F. iier 224 feet, or C. per 122 meters. This is deoidedly the slowest increase noted anywhere, but the temperature at a depth of feet in this case to be much higher than the average temperature of the air in Michigan. If the latter is contrasted with the temperature in depth a much more rapid increase is obtaraed. It is to be hoiied that more observations will be made on the temperature of deep mines iii the (Jold Helt. Many of them appear to bave a remarkably low temperature coiiMideriug the depth, and it was this observation that led to the experiments ha recorded.

Proe. Koyal Soo. London. Vol XLI. ltaBtPr.Mtt. Aw. Jour. Sci.. Vol. SLtll. IMt. p Ot. Am JMr.Sn..ViLUnBe..MM.r.aiB.

Oh A Pter Xiii.

<;KM;*iIS OK Till. KINS. AQUEOUS DEPOSITION CERTAIN.

It has beeu establiiibi'd in IVirmer <'liapters that the reins occur on flaaare syateins iu the rocks, produced by a compressive stress, and that thMe lIsBure systems are Uter tluui any park of Che pi43retaeeonB rook Byateni. The snb.'<taiic<'8 due to voiii formation are shown to in t country rock altered by metasomatio processes, in part fiUiug of preexisting cavities, the ores oonsisting almost exdnsirely of the latter class.

It has been aKsiuned that thee substances are due to the action of aqueous ur, more definitely, to certain solutions containing, diaaolved, the various metals and elements which are now fimnd on the veins. The torniatiun of qnartz veins by tln se a',''iicie.s is now so generally accepted that it is only necessary to puiut brietiy to the iiusts indicating mi origin, the only remaining altemativee being an origin by snbliniatinn or by gaseous emanation. Among these facts are the character of alteration of the country rock, including the removal of certain elements, aoch as sodium, the formation of hydrous mineraht, and the occnrrence of extremely abundant flaid inclusions in the qaartx.

Admitting the aqueous deposition as a faet. tlie problems ofteruig themselves arc the character of the solutions and their origin, as well as the cause of deposition*

Character Of The Solutions.

The filling of the veins, and especially the metasomatic rocks accompanying them, gives direct evidence as to the character of the solutions. The quartz indicates, of course, that silica must ha\ c formed an importaut constituent of the solutiou. The abundant carbonates and sericite in the altered wall rock show that carbon dioxide or alkallue carbonates, probably alst> calcic carbonate as well as potassium, must have been contained in the water. A iiortiuu of cl ar, massive quart/, without sniphureta, from the fourteenth level of the Merrifield vein, Providence mine, was examined by Mr. George Steiger lor substances soluble in water. the result that small quantities of siilpliates and chlorides were found, which in all probability were contained iu the fluid inclusion of the quarts. Sulphates must evidently alao have been m

CHARACTER OP THE eOLVTtCm.

coiitaiueil iu the watera. iSodium would also be expected from the viKoroQs leaching? of this metal indieated by the metMonutio prooesaes.

The of the ascending; waters found on the veins, in the chapter on the contents of the veins, are of interest as showing to some extent the charticter which, according to the above, would be expected of the BoIatloDB. They are, to be sure, odd ftod weak mineral waters, lac kiiif; in the amount of enrlKin dioxide and hydrogen sulphide which the vein-forming solutions must have jiossessed, and perhaps more the reenlt ef the leaching of the already formed Tn, bnt the rdative abundance of the carbonates and silica is eilg gestive, as is also the small amount of chlorides and sulphates.

Witters which have exercised such a metasomatic influence on the rocks in tlie vicinity of the veins and contained such large qiUU)* tities ( lit hoii as are rciiuired by the facts of tlx* metasomatism, are not known to occur in njtture except as ascending, nsnally thermal springM. That saeh was the character of the veia*fiMnBiBg solution is a ciMicluslon toward which not only one but several lines of reasoning lead.

That the waters were thermal also Indieated by the depth at which

the deiHmition must have lieen It is quite clear that the croppiiip of tln' veins — their — at the time of vein formation must have been tar above the Neocene surface. The amount of their pre- ITeooene erosion is difficult to estimate; fmm the geokigicsl hisfawy Ontlined it is apparent that vast masses of effusive rocks covered the region previous to the grauitic batholitio eruptions, and that the veins were fomied immediately after these intmsions of abyssal rooks. From these data a guess may be made that aboat three or four then* sand feet i-epresents the thickness of ro<'ks the deposition must thus have taken place at considerable depth, with a rock ternperntnra at least approaching F. Any ascending water at this depth must liave had a still liiplter tem|)eratnr'.

The alti'ration of the country rock is confined to a relatively narrow zone on each side of the vein, and gradnally diminishes in intoisity with increasing,' distance from the vein. This would certainly tend to show that the vein-forming solutions did not penetrate whole rock masses, but that they were eonlined to the |>aths presi'ribed for them by the fissures.

In (Jrass N alien there is a series of fissures of slijjhtly later age cutting the quartz veins. These fissures, called " crossings," are to a great extent open highwnsrs for the atmoepherie waters which have been circulating on theiit for untold apes and still have not been able to them with quart/, or ore. The existence of this system is one of the strongest iKNWible proofs against tlie theory of lateral secretion in its narrower sense, implying a leaching from the country rock by atmospheric wators and deposition of ore by these watere In the lls-surcs.

174 OOLD-tjUABTZ VEINS OF N£VADA CITY AKO OfUSS VALL£Y.

Origin Op Thb Mbtal8 And Oanoub.

Admittinur that the vein-foirmiiiR waters were amendlni; thermal

waters, the next question is, whence they derived their loud of dia- Molved subMtancee. The above diseasaioa shows that the leaehinj; by Kurface waters of the country rock in wholly inadequate to the vein phenoiuena. Bat it might be supposed that the contents of tlie veins— esi>( inlly thf uml metallic niiiieral'i — have extracted from the immediately Hiirruuudinif ru<:k8 by the intense ehemieal action which Is admitted to have taken place. This mpla nation in the first place, wliolly qnantitatively, for it is inconceivable that the relatively narrow /one in which the microscope shows that alteration has tiiken place should have furnished the large quantity of gold occurring on the veins. In the second place, the occurrence of practically itleiiti( ;il vein fillings in a dozen rocks ttf the most widely diOering chuntcter aud age cuuHtitutes the strongest argument that can be adduced against the immediate derivation of the gold from these rocks. Other fat'ts, such as the change in ohaneter of the filling iu one aud the same rock, tlie same way.

According to the analyses, barium is found iu notable quantities in the granodiitrite, and baritc should, aooording to the theory of lateral secretion, be found on tho veins. Vet no specimen of this mineral lias been collected from any of the veins, and, indeed, iu the altered country Tock that has been exposed to the aetlon of the aolntione the amall percentage of barium is only slightly decreased.

Iu the basic augite rocks gTwna of copper pyrites are of rather common occorrence, and copper has been fbnnd analytically in two of the examined diabases. Accordingto the theory of lAteral secretion, copper pyrites sin mid he ubiiiMlaiit on the veiiis. yet in many of the veins in diabu.sti clialcopyrite forms an insigniticaut part uf the sulphureis or is praotieally absent. Two snbstanees have, however, nnqnestlonably been from the eoniitryrock by the solutions, namely, silica aud sodium j iMssibly also other metals, but the latter iu quan* tities wbieb are so aamll as to be of no Bitfleanee fbr the viriu Ailing.

Rarer Metals In The Rocks.

It is quite possible that one or several of the rocks of the district may contain gold and silver or other heavy metals, and it is to be

regretted that circumstances prevented the contemplated extensive series of tests. The occurrence of copper iu two dhibasie rocks from Grass Valley has already been referred to. Mr. George Steiger carefillly eiumined, without any resultH, the granodiorite from Shurtletfs barn, one-half of a mile KSK. of the office, Nevwla City (also anulyzeil, see Chapter X), for rarer metals, using a of 10 grams in aqoaiegia. A coarse-grained diahasic rock with fresh angitefbrai the area south of Banner Bill was also examined in a similar way, with no results (59 N.C.).

RARER METALS IN Tlli:

A series of assays was carefully made by Mr. C. Wlutebeud, the aamyer of the mint with a view of flndin luinato traces of gold and silver. The grauodionte from Sliurtlcirs harii, Nevada City, gave no rpsiilts. Tlio uranodionte (loui Kate Hayes Hill, draws Valley (4!M'i. V.), cou tamed uu gold, but U.J ounce of silver per ton. From appearances this was thought to be a very fresh rook, bat the analysis shows a little pyritc. and tlie microscope shows a decided Ke'imiiiif itf s( ri( iti( and cblontic alteration. Fresh diabase fi-om souili of Uauuer llill (5U N. ( '.) gave no reenlt; nor did a nralitio diolNwe, containing a trace of copper and nuicli pyrite, from Leeman's tanoh, Diamond Ravine, west slope of Osborne ildl, Cirass Valley. A 8mewliaf ddoritic from the seventh level ot the Idaho shaft, 2U feet Irom the vein, gave no results. A breoeuftof argilUtOMici porphynte with abnndant pyrrhotite, oocnrriug on the lower road Just east of the little gnlch feet sonth of Bauuer llill, was next assayed. It has been that this pyrrhotite is not dne to the yein-fbmiing agencies, bat is of earlier date and contemporaneous with the dynaino-metamorphism of the Jurassic or Oretaoeous igneooa rocks, which, again, took place before the granitic iutrnsions. Pieces rich in pyrrhotite were selected, and a trace of gold, and 0.4 ounce of silver to the ton were obtained. The locality is, however, nearly in the (iiitinuation of the veins appearing just west of the suuiuiit of iiauuer llill, auU it would be difficult to assert positively that it did not contain small seams and flssores along which the vein forminr solution could have penetrated, so that, while suggestive, the result is not decisive. The main difficulty in the way of these tests is to obtain satisfactory material, positively from joints and seamSfbywhiili the auriferous solution could have introduced.' A local segregation of pyrite, e])idnte, magnetite, and chabazite from the iStar tunnel in diabase the Omaha mine, which certainly also belongs to the phenomena of general metamorphism and not to those <it the gold (juartz veins, was assayed (L*4 (). W); it contains no gold, but 1.20 ounces of silver. It would be of inU;rest examine the quartzose sandstones of Grass Valley for gold, but here, again, the difficulty of obtaining satisfactory material is gi-eiit.

Though fragmentary and unsatisfa<'tory, these results seem to indicate thai traces of gold arc not common in the rocks of the district. They ftuflMr seem to indicate that wherever anything is found it is silver and not gold which ])redominate8, while the reverse is true of tlio veins. It is believed that both silver and gold occur in very minute quantities in nearly all rocks of the districts, and that the pyrite and pyrrhotite developed in them by metamorphic prooessss, not hydrotherttial in character, contain this silver and gold as a concentration, lint it is not believed that the bulk of the mt tals of the veins is derivetl

Pyrltifcnmi t mhh il i ' .h i r 1 1 t*t r u 1, I'tjir.-r I "oiint v " f*imilur n*iinlla ; fur iniitan*'*, 010 iiunrc All unci a, Jn iimii A h i ir. rt<'. nth nil. Urpl. 1' . I i . .il .<iirvi-v. I'art 1 1, Ih'M. .153. It III twliTMl that llir pyrilm in tbeMS ruvkii iu due, not tu Teio tumutlioD, but to goiierml aetm-

M'liliiM fwilag tt.

176 Oold-Quabte Trins Op Vbvada City Amd Usa88 Vallbt.

fruiii thf: rockn iuimetliately atoiiiing the vein. Their origin imi8t 8till be left an open question; bnt the probability is ttmag that they were

ili8so1v'il from t!u' mon* deep seated of the raixxlioritt'. whicli aipeurtt to form the foundation of the Sierra Nevada, and brought to the arfhoe by the thermal waters, the whole process being the okming ehepter, tlio lat manifestation, of the abysHal granitic intrusion. In other parts of the world a connection has been established lietween acid rocks, Huch iis granites, quartz-porphyries, and quartzdiorites, with the gold veins ; and metalHo, anqneationiibly piiiDaiygoldt has been fount] in sudi rocks.

Further tiueslions uot yet solved are, hrst, the remarkable enoe of the goid-qnartz vein on the extent of the metamorphie series, shown in tlie paper on the " ipiartz veins of California;" and second, why, if derived from deep seated rocks, daor and bor compoumls should be so universally absent.

These views do not imply a derivation from extreme depths or from tliehyjMithetical "barysplifre." The thermal waters rising on the veins were doubtless surfai-e waters from the higher portions of the range, wbieh {penetrated to a eonslderftble deptii before reaching the snrfaoe again, but a few thousand meters would be the fireatest depths attained by them. It be borne in mind, however, how extremely nnsatisfiuitofy ear knowledge of tiie dronlatfofi of de seated waters is.

Solubility Op Thb Ganoub Minbbal8.

Aooording to Fnchs,' amorphons freshly prepared silica Is solnble tat water to the ext<*iit of 130 grams per ton. The natural siliceous waters show, however, a far greater solubility; the Iceland geysers contain lip to grams ton; Steamboat Springs. Nevada, 30U, and the Yellowstone I*ark geysers up toSMO. The silica in the latter is not pre- l ijtitated by rollin;:. even to freezing jKiint. when not exceeding grams per ton, attcording to A. Gooch,' it is pi*obable that the oomponnd is not contained as alkaline silicates, but as free hydrated silica. Saturating the waters with or 0O did not produce precipitation.

Calcic carbonate is slightly soluble in pure water at ordinary temperature i'JXH) to .'HMI grams ton of water, In water satm-ated with carbon dioxide the neutral carbonate dissolves under fonnntion of bicarbonate at the mte of U.SH gram to the liter, or practically 880 grams to the ton.* With a small percentage of lodge or magneslc sniphate the capacity for solution is nearly doubled.*

CliriiiiiMini M ini-niloKii-, l.<-ipiiK, IWW. p. Ik*

triiM-iilii.'. i-lc, W. H. WmsI : Ninth Ann. Krpl. 1'. S. Survey, p. 655.

*RoMOcaiiil S hni It-iiinirr. Vol. II. p. 'lOH.

T.StatT}' Uuul. Am. Jour. Sci.. Sdw r. Vul. XLll. p. Si.

Genesis Of The Veins.

Rblation Of Solubility To Increased Prbssurb And

Temperature.

It a widely accepted view that iu general the decrease of pressure temperature forms au important factor in the fomuitloii of tnineml

depoHits by aaceiidiiifr hot Mprings. In view of this, it may bo profitable to iii<|uire how, as far as wo know, tlif solutions of difltTcnt are iutiueiu-ed by tlie iui-retkHe of prcHisure aud temperature.

It is proper to clrw attention at the onset to the faet that the qnestidii is exfn'TiK'ly coinplicati'd. for the i' of other sniisrances. as a rule, aQ'eclti the solubility of auy given salt; so that the rules nbiuiued firom tinple solutions of certain componnds may not be applicable at aU for SOhitlon.s of the same in mineral waters.

Pressure certainly allVcttlit- solubility of many substances. but the retiult may be either uu increase or u decrease. The iuvestigatiuii of Bnuin I shows that rate of increase (positive or nettive) is a Amotion of the pressure. heat ot' solution, and 'han;e of volume takiug place iu the solution. It oontravtiou takes place, which Is the less common ease, there Is in general a decrease of solnhflitjr.

Ive;;anlini; silica, there are apparently no data available : di |>o6ition taking piac t- from highly saturated Solutions may be doe to loss either ot heat or of pressure. ,

In the ease of carbonates, and especially calelte, pressure Is said to increase the solubility in water satnrat( with CO.. but only up to a certain degree, the maximum amount that can be dissolved being 3,U00 grams per ton.* Sodic chloride shows only a very slight increase in solubility by iit<'re;ising pressure. Sodium common in the mineral waters, sliows a distinct dei-rease in

The intlueuce of teiupeiature hiis been more e.\tensively studieil. It may he said taft np to about lOOO. there is in genera] an increase in solubility, but recent experiments seem to prove that for many substjiuces there is, in fact, alter a ctertaiu point haa been pa-sseil, a distiuot decrease.

No results are known in regard to ftiliea. Onlclc carbonate shows a slight increase iu solubility in pure boiling water, one part being soluble in 1U800 cold and 887o parts of boiling water (Fi-esenius).

On theotlier baud, Engel and Yille' have shown that increase of temperature decreases the solubility of l arbonates, especially magiiesian carbonate. Sodium sulphate shuwtt, according to Uuy-Lussac and otbersi* an increase np to 3So, then a sadden decrease and nearly constant aolnbility np to

The other sulphates show similar relations, aeconling to Ktard. Sodic, calcic, and fivroos sulphates, for instance increase in solubility up to between 60o and 1200, ftom which a gradual decrease begins,

OMmdd. AllKemelnr Cbeiole, lotfi Allxrnirinr Cbrmir, KMX.

Mmmt and SehorlmaMr, Vol. II. p. m. OMwaU. AMfwl— Cbudik 9. lOtO.

178 OOLD-tLAKTZ VEINS OF NEVADA CITY AND GRASS VALLEY.

potauic aalpbate aloue increasing steadily up to 200°. Sodic ebloride increases very slowly in Mlnliility up to 100. Applyiu;; the formulas of vapor-tension to the prohleia ol mlobUity, Le 'hatclict ' arrives at tlie result tliat, in ireiieral, the <'nrve reprpsentiiijf tlic solubility will rise ui to a wrtaiu limit at lOO'' C. or you (J., aud then gradually sonic again.

Assniniutr a Tiiiin'ral water cnn'r.'inp: at tlio siirfaee witli a ti'itiiieraturo near the boiliug point aud a gradually rising pressure and ternperatora down to a depth of several thousand feet, it beeomea dear that we are not in the least justilicil in assuming a gradual and iudeflnitely extended increastxl solubility in depth, or, reversed, that conditions for deposition will gradually become more t'uvurable as upper levels are reached. It in tet more probable that fat temperatnrea rising high above W)' aiul uiider inrreasin;: pressures there will be a decrease iu the dissolving power of the waters, at least as far as the principal eonatitnents of the water are concerned. In all probability the ijuartx veins here described were deposited from solutions at great depth below the snrfai*, under strong pressure and at temperatures ranging perhaps from 100° C. up to 250° C. It is tnie, and the feict agrees with results previoQsiy stated, that at the month of the crevice deposits of many substances are formetl by suddenly diminishing but it does not at all follow that a diminution front 200° O. to WOP C. trill produce a result similar to that of cooling from IQQo to 0'. Besides, the precipitation at the surface is very largely caused by the oxidizing influence of the air, of carbon dioxide, evapot** tiuu, redaction by orgauic matter, and algous growth.

8Ynthbbi8 Of Oamoub Minbrals.

Quarts has been reproduced by Ohnrastdioff, Doelfeer, Senarmonti and oCbers from alkaline solutions of silica or by reerystalli7.ing gelatinons

silica. According to Doelter,* quartz can not from aqueous solutions at a temperature below 2%i0° 0. The acts hardly appear to bear out tUa assertion. At StSMDboal Springs there are vast masses of siliceous sinter which are distinct surface a<-nirintlations aud scarcely can have been found at a tem];>erature jibove lOU' O.— more probably Tet this sinter oonsisCs of a mixtnre of preivailiDgopal and cbalcedonite, with smaller masses of finely grannlar quartz, often with crystallogrnphic outlineji. Small quartz crystals are found in the silicified wood of the auriferous gravels, where the temperatnre can hardly have been very high at any time.

Opal or silica may be dejiosite*! at considerable depths, aii its occurrence in several dwp mines ol Grass Valley iudi-

Oatwald. AUgmnalae CtuoDis., p. 1007. LM.tit..V>.lM.

Solubility Of Gold.

cftteK. Doelter's experiment OH the wlabtli of gold, noorded bdow, indicates the same fact

The different carbonate minerala may eaaily be reprodnoed at oidinaiy as well ae at bigher temperatoxes up to 500 O. (Friedel).

Solubility Of Oou&gt;.

CoRMerlng only the mhwntB common tn mineral Kraters, it is fbirad that gold is attacked hy many of tbera. Eglestott found a nliglit sola bility of gold in Rodie and jtotassic rlilorido. as woll an in iiinny other HaiU ut' IcHH for the present purijose.' Doelter has lately Amnd tbat gold Is soluble In a 10 per oent solution of sodio carbonate heated forty-seven days in dnscd iron tubes at L'.'>0' (',; also in a aolution of 125 c c. water containing carbonic acid well as 8 per oent sodio oarbonate and 3 per cent sodie siUcate. In this latter experiment the gold was dissolved at rate of 21.5 grams |ier metric ton of water. In vhe first exjierinient \yeT cent of the gold uswl was disaolred) which, under the assumption that a similar quantity of water was used (not expressly stated in tbe original), would give a solution of 413.4 grams per metric ton of water. TheseflgoresOoneepondtoaTaloe of I3.:v.} and $20.28 livr ton of water.

An extremely interesting ftatore of the last experiment was that

upon opening: the tnhe a few mtiMitf crystals of jold vvcre foiiiul, which in all were newly formed, and further, that small crystal aggregations of quartz bad formed, aa well as a large mass of hydrous ailieiu acid in globular concretions. In this as well as th(- following experiment on sulphides the beating was carried on oidy tluririf,' thf BO that the interruption of the process may have had something tu do with the deposition of the newly formed aubetanoes.

LivorsidfTi' ' also found that gold was dissolved by sodie silicate, but it is doubtful whether this reaction is of much importance, as it is not at all likely that tbe alkaline silicates can exert in tbe presence of carbon dioxide.

I'reviously to Professor Doelter's experiment Dr. G. F. Becker' had found that gold is relatively easily soluble iu Kodic aulpiiide (KaiS), a sdntion containing 843 parts of the latter dissolving 1 part of gold at ordinary temperature. Gold also, according to Be(!ker, dissolves at ordinary temperature in sodic sulphydrate and in solatious of sodio cartwnate partially saturated with sulpbydric add.

Solubility Of Sulphidk Minerals.

Doelter found that pyrite, galena, autimonite, sphalerite, chalcopyrite (in part), arsenopyrite, and bonmonite are to some extent soluble in pore water, when heated itar almost foar weeks in glass tabes to a

Trana. Am. lunL Mln. Eni;.. IMo, VuL VIII. iSS

Piwi. Bojal Boo. Xev Smith WiIm. Vol. XX VU. UK, p. ua.

um. V. a oml anwtj, V4. xm. um, r. m.

Oigiiizea by

180 Gold-Qi Ahtz Veins Of Nevada City And Grass Valley.

temperature of 80= C. Aboat one-eighth or one-tenth of the reinaitiing tlnely powdered mineral was in addition usually found to be raerystallized. Pyiite was aduble at the rate of 1,000 gnmB per ton of sointin. or o.ioperceut The solutioii of fakoa coDtained 2T0 grams of i'bS per ton.'

Aooordhig to the same aaibority, galena and pjrrite are also to some extent ttaokel by water containing carbon dioxide.

Beoker' found that pyrito is soluble in cold Hohitions of sodium sulphide. Ten cubic cm. of solution containing 1 .0955 grams of sodium snlphide dissolved 0.6 gram of pyrite, tiie solution thus containing about 60 gmiiis of pyritc jicr ton, or 0.000 per cent. Pyrite is also soluble in hotsodic .sulphydiate, but not in cold, and is relatively easily soluble hi cold and ho solutions of sodinm earbonate partly saturated with hydrogen salphide.

Similar results were obtained with the .sulphideH of mercury, copper, zinc, and, of coarse, arseuic and antiuiony. The sulphides of lead and silver could not be brought in solution, the former not even when heated to lOO' C. in closed tube.

Doelter's later experiments show that pyrite, galena, zincblende, arsenopyrfte ohakopyrite, and boamonite are all soluble in solo sal< pbideby treating the finely powdered minerals for tweiit.y four daj's of twelve hours at a temperature of O. in glass tubes. Quantity of mineral used, about 1 gram ; quantity of liquid, about 40 to 5U c. c Of the pyrite, 10.6 percent was dissolved, corresponding to nn approximate content of 0.2 per cent pyrite in the solution. Galena is even more soluble, in comparing these large amounts with Becker's results it would thus seem that time is a very Important factor In the solution of these minerals. In regard to the solubility of tellurium compounds, which evidently have a close relationship with the gold, there are uo data available.

Effects Of Increased Pressure And Temperature

In rcg.iril to the intlneneo of heat and pressure njwn the solubility of guhl and sulphides, there are but few definite data available, and, in Ihct, the problem is mnch more diffloolt than that offered by the ordinary easily soluble salts. The experiments by Becker and Doelter indicate that heat, and perhaps also pressure, increases the solubility, but how far this increase extends is ulmoNt entirely unknown. It is not anraasonable to snppoae that, as with other salta, this inereaae Is not indnite, bat reaches a maximam and then again declines.

Tadwnnslu nial UUthiil. IMi VaL II, p. SM. Uc ciL, p. 431.

Genesis Of The Veins.

8Ynthb8I8 Op The Sulphides.

In diaonBsiiiir aolnbility of the metallic minerals, eepeofally the

RuI])hide.H, It has heeii taeiUy aasumed that they might have been formed simply by separating ont from their solvents hy changes affecting the latter. This is certsunly not tlio only way in which they could httve been formed in the veins, as is proved by the relative ease with which most of tlieiii cuti be formal synthetically in tlie wet way, chiefly by the action of sodic or hydric sulphides ou different salts. Pyrite, galena, ehaleopyiite, argenttte, tetrahedite, twiinionfte, and aneaopyritehava been obtained by Senannont and Doelter in thin manner. Pyrrhetite requires for its formation the presence of an atmosphere of carbon dioxide or of reducing organic substances, entirely preventing t3ie change ftom ferroas to ferric salts.

This is interesting in view of its extensive presence in metamorphosed argillites (Fetleral Loan), and in view of its entire absence from the veins (exeepting a seam of abntHnnal oonporftion in the Grown Point mine). Even the veins in arpillite (Federal Loan) dii not carrj' it; the pyrrhotite of the metamorphic argillite, close to the veiU| Is also, remarliably enough, converted into pyrite.

Marcasite has not yet artificially pivodnoed; nor haasfaioblende; wiirtzite, the rhombic modifloation, however, Doelter soeoeeded in obtaining.

The reaetion by which the oxides of iron or other Iron salts are eon*

verted to pyrito by the tion of hydric or sodic tyilphido is evidently of great importance. This reaction was shown by Dr. G. F. Becker to hare talcen plans to grestoxftentte the altered oonntry rooks of the Comstock lode, the pyrite being principally, apparently, derived from the ferrous silicates; it was experimentally verified by Doelter* in case of oxides and Ciubonate of iron, it is clear that the ferro-magneslan siltoates and liie magnetite in the neks have IhmiSlisd the greater start if not all of the iron for the pyrito in tlie altered rocks, while it is equally certain that comparatively little iron has been carried Unme the eonntry reek in the vehi.

Precipitation Ok The Gold.

There are many experiments recorded as to reactions by which gold oonld have been precipitated from its solutions.* Ferrous sulphate is one agent. This is, however, too complete and sudden a reaction to be to have a general imiMrtance in the formation of the pnld veins. Precipitation by organic matter in the wall rocks is another, and theblaok .ilates along the Mother lode have been extensively quoted as a suitiible cause for the deposition of gold. There is reason fo believe that the importance of this reaction has been greatly overestimated, if

' CIumIbIh Iftiniilntlt, p IIB

flM.S Swttl wiiai,vLxzvn.un.p.m

1 82 Oolu-Quartz Veins Of Nevada City And Valley.

indeed it is of any iinportuiice at all. Tlic carboiiaoeons ai pillite of the Neviulu City and Jianuer llill districts uQern aii excellent uriteriou,and it does not appear to have the leaat inflneaoe on the tenor of the quarts in that nx'k, wliile oflur voitis wliolly in iiiassivf nn-ks and far away from any i-arbouaceous matter may be much richer than those in the Hlute. Certain experiments by Wilkinson (1866), Coemo Newbery, Skey, and Liveridge' Hhow that pgrdte and also nearly all other salpfaide minerals, ijirlmliii-,' galena and nrsenopyrite, will prociijitate pold from Mulutiuus of auric chloride of vuryin; concentration, i hi.s reaotiou is probably of oonaideraUe Importanoe, as it explains the strong pen utae of nsnally contained in the anlphnrets in a state of minute dissemination.

Many other proposed reactions miht be cited, bat they of qiiostioiiablc viiliu' in speculating on the particular combination in which the gukl is contained in the water. According to the views of modern chemistry, wutry solutions of salts, even when only moderately dilated, contain tiie solids in state of diiaodation. Salts of gold could probably not exist as such in the mineral waters.

Mods Op Deposition.

In disenising the node and cause of depodtim, it nrast be acknowlwaged

that we have to dealvith data only imperfectly known, and that the conclusions drawn from them are not yet more than a Bearing in mind all the facts adduced, it seems certain, however, that the deposi t ion has been elVet ted by tbennal water containing carbonates, silica, iuitl sulphurettMl hydrogen or sodium sulphide, and containing also uieuiuruble (quantities of gold and metaliic sulphides, it would carry ns too far to discuss the origin of this water and the source of its const ituentw. On the whole, flic views of Daubreo and seem the must reasonable explanation. In the words of the latter, "The ground water descends by capillarity through the rock intersUces over large areas, to mount again through open channels at a few mints."-

Dnrinj their long descent to heated the waters liad ample to dissolve the substances contained iu the rocks, and iu this case probably obtained their gold and other heavy metals the

granodiorite at ;;reat ileptli.

It most be confessed, however, that the large <iuaiitity of carbon dioxide and snlphureted hydrogen carried by many thermal waters is extremely didicult of explanation. During its downward course the water"scan nut have taken up on the contrary, descending surface waters in a short time are deprived of their COj by the forming of carbonates. It is not probable that extensive bodicB of limestone ocour in

depth in this icinity.

It has been .shown that Nem-ene erosion had removed a great

A. Lirenfalg*. Proc. Rojral Soc New South Wait*, Vol. XXVU, 1883, p. 303. tQMMU ut an dipMllii TraM. Am. bat. Mia. Bag., Vol. ZZm. UN, p. m.

MODS 09 nSPOSmON.

18S

deal, probably a couple of tboasaod feet at least, uf the parts of the gold veinB, and that the lerda at which minion; ia now carried on

Mcri" from to 5,00() ft-et the oritiiiial ajicx. Witbin tills interval there is certainly no cbaite iu tbe quality of tbe 111' above water level), nor can it be said that a change in quantity has been definitely proved. Witbin tbe limits of explorations by (Icep ininiiifi mo definite ])royri"(*f*sivo cliniipp in the ebaracter of tbe ore or of tlie ultcml country ro<;k lim been iound, such as wonld nndoabtedly exist if the cause of depoaitioii wwe (lecrcasing ]ressnre and temperature. From tliis, as well oS flrom the results of tbe investigations of solubility of tbe Uifl'erent sabttaaoesi it maj TeBaoiiablj.be concluded that an nndne importance has been, attached to the later seduetivu pbmse "deposition by decreasing pres-snre and tomperatureT tlionpli it is not to be denied that the depoisitioii may be iu start u I'uuctiou uf these variables.

The netasomatio action on th wall rocks is nndonbtedly of great imjMjrtam-e for the The facts stated several time'* before sbow that tberu is but very little free gold iu tbe altered wall rock and very little gold in its snlpbnieta, while the main amount of the gold and the aorifiBrons sulphides are contained in tbe quarts filling tbe fissure.

It may bo possible to consider the walls as forming a septum {>ermeable only for a part of tbe solution, according lo the osmatic laws,*

fnr tin-substances which act chernically the minerals of tbe rocks. The lutter in general ar sbuwn to be permeable lor the carbon dioxide and alkaline carbonates; also for carbonate of calcium; fbrtber, for hydrogen suljdiide or sodic sulphide, and for arsenic sulphide. On the otlier hand, they are less permeable for silica and gold, and almost entirely impermeable for tbe other metallic sulphides. This suggests tbe possibility that tbo bydrated silica is contained In tbe water in -solution. Suljihide nf unM in cnllriidal solution, iuiiH-Tmcuble tur the ordinary )>archuieut meuibranes used in the dialyser, bos been prepared by Dr. E. A. Schneider.* It might possibly have existed in the waters, though the is that it would be by some of the <-onstituents of the mineral waters. It is also known that the sulphides of the heavy metals iu general can form coHoidal solutions/" However, tlio ijrojiertifs of colloidal solutions are only imperfectly known, and it is doubtful whether ciystallisatioDcoald take place iu such solutions.

By metasomatie processes the wall rocks absorb carbon dioxide, jiotassium, sulphur and lime from the vein soliition.s. On the other band, there has been a steady accjuisitiou of sodiutu (probably as carbonate) and of silica, abstracted ttom the wall rocks. The result of

*Dt. G. ¥. BmIiw flnt introduced Uil* cuoeeptiun applied Iu llie ulnenil ilcpoaits, and It (iruiuksca to be of Knat importance for thn dlMaahw af tKetrewi— 8— wSiparili" tai lfli anl Raiaarcee U. S. IMZ. p. St.

*BaU. V. S. OeoL Sanrojr No. p. ML

'IhiU. Boa. eUmiqna toL 4a. im. p.

184 OOLD-QUABTZ VEINS OF NEVADA CITT AND GBAflft VALLEY.

ttie wludeprooeasiraiild probably be a concentration of the vein solutions and {iroprpssivo an nmulatioii of silica. As far as tho chief coiistitiieuia are couceruetl, the vein solutions were very likely highly conoeatrfttod. The deporitioii of ailica wnm pcolHibljr parfljr mnwd by mn uubalancinp of tho dt'licatt-ly atljust<*d conditions in a concentrated solution of ilifl'crent compounds by the new material from the wall rock, and ]iui tly by varying conditions of temperature and pressure.

The metallic aolphidea and the gold ( arried by the silica were prob' ably to a preat extent jirecipitatt'd intclianically by the crystallizing quartz. The intimate connection of the gold with the sulphuleii was very likely eased by the experimentally proved tendency of gold aolntiouH to bo pre<!ipitated by of sulphides.

The oooDes to which the occurrence, form, and directiou of the ore shoots aire due are very obaeare and to extend Ifte disemsfam to them would be to go fivther in the realms of hypoCbesis than is hece desirable.

PKTAI LKI) BANNER HILL DISTRICT. VT.mS OF THE TRRRK RA8IN AND WILLOW YALLEV.

Oenera{ /enturrx. — Tliew veins have in Reneml an eat-we.st strike and flat mediant northerly or southerly dip. The oren are fre<|uently of high grade and the fiswures narrow. The gold aswociattHl with much silver, and there is a considerable amount of anlpharota. A few veins having a north-south strike and flat westerly dip intersect the

Fio. 10 aiiaetod (oiMi In (rrMimllnriU, Deer Creek. IMIrfonntain mlns.

prevailing system. The east-west veins are in closeHt genetical connection with a system of joints or a sheeting of the country rock; this sheeting begins to show very strongly a little beyond the Deadwood mine, and may be seen to best iwlvantage all along the rocky canyon of Deer Creek. Tig. 10 illustrates this structure; granodiorite is divided in benches or sheets from 1 to 4 feet thick and dipping north at slight

28

18G UOI.l)-(iUARTZ VKINS OF NEVADA CUT AND OKA8S VALLEY.

aogleM. Opposite tbe BellefonDtHiii mine tbe strike is N. 78' E. and the dip 30° N.; at the Leoompton mine the strike m east-west and the dip 30° K. On the Federal Loan road opptwito the big bend, 000 feet w'8t of till' contnct, y. <;8Jo K. and 35' N. wus noted; here the sLeet ing aeema must In a width of L fout six or more minute Meams vera aeen, dlppinir m stated, end each miurked by e sUnsfat bleaeUng of

the gnaodiorite aixl by a flnn string; of iron pyrite. The tiormal Kruno* diorite does not contain any pyrite. This sheeting coutinaes unbroken across tbe contact, bnt the direction swings a little more to the northcaBt and the dip Itecomes decidedly steeper, ap to 68. Beeides the joints (lippin} north. aDotlxT set now begins to ajqiear, about parallel to tbe tirst in strike, but dipp'*ig soatb. In a fresb exposure of black, bard metamorphie raek on the ditch 3,000 fhet eaBt-aontheut of the Federal Loan, tbe following dire<'tion8 were noted, tbe sbeet being about 6 inches thick: (1) Strike N. 68° E., dip 70° N., and (2) strike 08° B., dip (HP 8. The displacement which has taken place along these joint phuies is probably in most canes very alight. Aeoend* ing waters have foriniMl the most veins along those fissures in this joint system which otl'ered tbe easiest channel for their piissiige. Tbioeis always a strong possibility of finding veins parallel to and a abort distance away from those exploited, cross cutting should eoasequently not be neglected in working the deposits in this vicinity.

T7ie Federal Loan vetH. — Thls Is an old location, workeil many years ago, but not opened on a larger scale until 1890; it has at ])resent a 10 stamp mill, and the total ont|)nt is stated to be !*l7."i.(>(K>.' The mine is developed by an incline shaft, following the vein down fur a distance of 800 Ibet, and by drifts extending from 100 to 400 feet on cachside. The ninio is only u few hundred feet east of the granodiorite oontact,aud tbe country rock is that black or dark-brown, hne-graiued, naesive, slliceons argillite described in Ohapter Y. It is somewhat influenced by contact-raetanKU'phic action, which has given it a slightly coarser texture and browner color, tlie latter caused by tlie develoj)- ment of Itiotite or brown uiie,a. Dikes ul course, dark Uiortle are met in the drifts of the mine. Pyrrhotite is distributed tbronghont the country rock in niinnfc grains. Tbe vein, which only near the shaft, strikes somewhat north of east and dips south at an angle of It is very Irregular in width, sometimes showing several feet of massive quarts, then again cloetng down to a seam, or also frequently breaking up in a mass of stringers, which may be mined and milled as a whole on aooonut of the gold contained in tbeui. Tbe wall rock itself contains hot little gold.* Tbe rook in the immediate vidnity of the vein

is Irregidnrly altered to a grayish material, often cut by small calcite veins, and contiiining much timely disseminated pyrite and arseuopyrite. Thia rack is examined SMwe in detail in Chapter XI. The

Of. SiMWik B9t> SUM MJonaloitat, y.

lianging wall of veiu is not well defined, bat the foot wall contiiiUM nnbrokeii ami distinct. Nninerons seams dipping north at various angles, but carrying no quartz, are notd, h8 illuHtrattd on tig. 11. The minernl spring on the fionrth leral is descrilied in Cbspter IX. Ttie filling of the vein consists of the usual niilky white quart/, ofv usionally containing grainsof calcite. Fragmentsof theconntry rock, sharp and angular, though converted into carbonaten and aericite, are vey Arequeiit in the quartz, iii il khiuhI these fragments tlie snlphurets often cluster, as illustrated in I'l. VII, llg. b. The ore contains the large amount of G per cent of sulpburets, which have a very high percentage of arsenopyrite and are of medinm grade, containing iomewliat nuwe gold titan silver by weight. (For analysis of roneentrates, see p, 127.)

Arsenopyrite and pyrite prevail, while galena, ziucbleude, and eopper pyrites are very 8nbordi> nate.

The ore shoots are somewhat irrepiilar. but the best pay is found In a ehinney in the vicinity of the shaft, dipping about 70 B. on the plane of the vein. The value of tiie ore is Stated to be per ton.' The gold is iiia tine.

Th ConttHuHom nd Lerant rlojina.— The veins in the vicinity of

the Federal Loan are not. as a rule, traeoalde on the .surface for a long distance. North of it lie the claims just nieutionedt located ou veins belonging to the flsanre system, dipping north. Some good ore is reporteil tu have been found on the Oonsdtntion in former years, bnt the developments nrc sli<,'lit. There appears to be in this claim a unmber of small inirailcl lissure*. The country rock, which is a dense, siliceous argillite, is intMregnated with iron pyrHea along the veins. In the ndiit report of 188U the vein 1 fiiot thick, heavily aalphureted, and similar to the Lecompton.

The Lecompton vein, — The Lecompton fs situated on the sonic side of Deer Creek, almost ailjoining the Federal Loan. It was located in 1867, and up to tlie gross yield of the mine was From 1863 to 1860 it was also a considerable producer; in 1867, however, the indine situated near the bed of Deer Orsek was flooded by a ih6diet

Bmolb Jtopb aiKto aOaMdgglrt.

188 Gold-Quartz Veins Op Nevada City And Grass Valley.

the improvements destroyed aud iiu work has beea done since then. It is credited in the mint reports of 1880 and 1890 wllh prodnetion of reqMOtively $5,350 and $900, which amounts probably came from remaining jiillnrH of ore in the upper workings. The outcrop of the vein, owing to the tiat dip, forms a curve high up on the slope; the ore in tbis part of the vein wm decomposed and very rich, and has been by means of Tuimerons tunnels. the rrcok Icvt l the vein was opened by an incline near the east end of the claim, 275 feet long. There is also an incline 900 feet long near tiie western end. The vein is contained in granodiorite, strikes eastwest, and dips 38 to 40' X. at the ea.st incline. It is only from 4 to 8 inches wide; specimens show excellent comb structure. The gold near the surface had a fineness of only 050, while in the deeper workings it attained ISO, The ore is stated to have contained arsenic and antiinony, and was very rich, the upper parts of the veiu averaging )40 per ton, and smaller lots mnning np to $400. Aooording to the mint report of 1880, the bullion contained 416 per mille gold and 584 per mille silver.

Between the Lecomptou and the Loan lies the Lebe), a vein in grauodiorite striking E. 23 S., dipping north, and opened by several short tunnels from the level of Deer Creek up on the side hill. Tlif" vein is up to inches thiokf of fair grade, and ooatains vary abundant aiseuopynte.

On the north side of the creek, opposite the Leoompton, there are a great number of old slopes and tunnels mn on narrow veins between the sheets of granodiorite.

The Bettountoin vei {formerlif the Ebavgh),—Thi% well-deflned vein Ues on the north side of Deer Greek, tiear the Lecompton. Liocated in 1857, it has been worked !it vals sine*' then. It is opened otdy by tunnels run in from the steep slope of Deer IJreek Canyon. The outcrop mna up the bin to an elevation of 270 fyeA above Deer Greek, and then crosses over into the Cyaiio claim : its direction is east-southeast, while its actual strike on a horizontal plane is east-northeast. The dip is 28 to 90O N. The rdn avcraKes 12 Inchee in width, and there are several small bat rich ore shoots; no ore containing less than $24 i.s said to have been crushed.' This, as well as all adjoining veins, i.s in granodiorite. Close to the veiu the ih rock changes to a yellowish gray, soft masa of still clearly diMemible granitie stmetare, consisting of serieite, some residuary (inartz, and abundant sharp enbical crystals of pyrite. (For description and analysis, see p. 148.)

Never Sweat md Omega rffiw.— These are veins parallel to the BeOa* fountain and located a few hundred feet farther north. The Never Sweat is ojjeiied by an incline feet deep, has been worked only on a small scale, aud is shut down at present. The information about it is obtained from Mr. J. Lyons. The eonntiy rock Is a granodiofila with considerable hornblende, and decomposes to a reddish SoU ct great

Msvate Cmu Mlatag Ruftow.

Banner Hill Dibtrict.

N.

depth, on uccoatit of which theuuturop cau uot be reailily traced ou tUe aorfiMMb Tb veiii is narrow, ham 3 to 16 Inches, and yidds aooie wry

hifrli pnuk" oro, tlie vnluc roacliinp $300. Generally similar to the Lecomptou, the balUou cuiitaiua some antimony aud much silvoTi being only 750 fine. The strike is N. TSo E., and the dip at first 48o N. At a depth of 200 feet a eroMH vein is streak, iH-loiigiur to the Federal Loan Bystem of fractuifs. arcnnliiig to Mr. Lyons, the vein leaves the original and continues uu the one dipping south (fig. 12). This is of great interest as proving,' that the two vi'iii systems are contempofaneona.

NearWillow Valley there are a of veins, uuue of which, however, have been worked very extensively.

The Montana vein. — This has been wmrked intt I itiittontly and has pro duced some good ore. It is developed by an incline shaft 400 ftet long; strike north-ast dip 22' NW. The vein is from ti to 8 inches wide, and can be traced for a cnnsidcrable distance across the contact line. Tlie ore, which in heavily sulphureted, forms two pay slioots pitching to the southwest on the plane of the vein, (e on eaeb side of the shaft and from 100 to 200 feet wide. In the dflim are three more parallel ledges

of less iinportaiire.

The Willow Vitlley vein {Tolbert). — Located in 1865, but little work has been done on thisyein nnce 1067 ; 000 tons wrae tiricen oat in 1866,

yicMiiii,' an average of $22 per ton.' It is developed by a 200 foot incline the vein strikes uortlieast and dip 45 to the northwest; its width is from 1 to 4 Ibet Theconntryroek is 'rauodiorite,tlieeaateni

end of the claim crossing the eon tact.

At the forks of the \Vasliinf,'toti and Scotts Flat roads is a small vein, striking 2s . 72 W. and dipping 70° N.,on which a little work has been done.

The FranVlin- Hussey rrltt.—'Snt much work lias been done on this vein since 1884, when some very rich ure, going as high as $100 itar ton, was produced. It is developed by an incline and drifts 280 ftet long and extending Oo feet on each Hide. The strike is northeasterly i the dip 46° jS W. The vein is in places from 1 to 2 iieet wide.

Fls.lSVwtied

190 GOLD-QUASTZ TBINB OF lOBVADA CITT AND 0BAB8 TALLBT.

The Buckeye vein. — This vein, which is opened by a 400-foot tunnel from Willow Valley ('ri'ck, has a northerly <Iiro<'t ion ami an eastpily flip of 45, both unusual lor this locality; it is iuclom.>d in horntelH uiul ia only few hundred feet feom tbe contact ; the width is flrom 1 to 2 feet) and ante good ore is reported from it. It can he traced from the oreek northward until it diaftvpears under the audesitic breccia.

The Tieadwood vefik— This vein, which is located ne*r the month nit Valley Greek on the north side of Deer Creek, has been a eonsiderable ])rodiu er at various times since 18-"i'>, but in the last leu years iiothiui; has been done on it. A lU-stauip null formerly existed on the property, and the total production ia given by Mr. J. Lyons as about The vein is by an incline shaft r00 feet loufr, a drain tunnel from Deer Creek, and aeverul dritU extending principally soutliwwd of fhe abaft fer 300 to 400 fe The vdn, which is in grranodiorite, crops on the surface, where it very Hat, in a northeasterly direction. Its true direction, as shown by the incline and lirilts, is X. 18 E., the dip being W. The width is narrow, ranging from a mere earn to 18 iDches. The ore Is highly charged with aulphnrets, carry* iiif: jiyrites, galena, zinoblende, and Mrsenojiyrite. also eontaininr some antimony. Tlie tenor is high, sometimes reaching $100 to $200 per ton. Moat of the ore has been extracted flrom the sonth side of the inoHne, while the northern side has been prospected but little. The bullion is 815 fine, which is more, it will be observed, than is iisnal in this part of the district. The t-ruppings to the east of the incline, which over a large area lay extremdy flat near the surface of the thoroughly decomposwl praiiodiorife, have been cxtensivply sluiced and even washed by the hydraulic process. According t4> Mr. Lyons, the vein is distinctly feolted on tbe tannel level to an aggregate amount of SO feet by four erosa seams striking a trifle north of east and dipping N. Tbe vein was found to be thrown westward going north on the drift, which would indicate a reversed fault with relative upward luovemeut of the hanging wall. The aeams are comprised within 100 feet; In the lower workings the same seams were found a little closer together; without doubt they form the continuation of the Texas vein complex. The workings of the mine are not now accessible.

The TexoH vein Kyntem, — About li miles east of Nevada City, on the Willow Valley road, there is a strong system of at least four welldefined veius, named respectively the Greek, Wheal, New York, and Delaware (Red, White, and Blue). All strike about east-west and dip north at angles varying between .'J'' and 50"*. Tlie developments are slight, consisting cliieUy of short tunnels from Mosquito and Deer creeks. The Kew York is opened by a 100-feot-deep incline (Texas mine). Some of the veins, especially the Xew York, are very In ;>vy, 3 and 4 feet of solid (piartz being met with; on the road a little east of the Texas mine the croppings are unusually strong ; in the best pay aboota tbe ore from thcae ToiDa runs Utom $$ to $40 and contains 4 per

URMiinr.f

BANNER RILL DIRTRtCT.

cent or more of Bulphoreta. TUe iJeiawiu-e fur euKtward over on the Marchie groand. These veins seem to form the startiBg

point for tlu' Willow Valley 8ystin, tli ori;;inally strong flssareB being replaced eastward by au extensive system of sheeting.

The Mvrekie vetMThis complex consists of two east-autl-west veins, the Big Blue and the Alicf Belle, as well as two north-sind-south veins, the Lone Star and the Indi'iHMnlfiice. The properly has lieen worked at various times since 18GI, tlie priucipul producer being the Big Bloe; flrom 1878 to 1884 the mine waa one of the largest prodnoers in the <listri<'t aiul had an 18-stamp mill ; detailed statements of its production are found in the mint reports. From 1884 to 1801 it wasahnt down but has lately started again, probably with the exitectation of using eleotrie power. From 1878 to 1884, 38,ooo tons were enuhed, eontaintiit,' or an average of 1.5 per ton, witli 1 per rent of hulpliurets, at an average cost of #1.60 for milling and $U for mining per ton. The anlphniets are very rich containing ftom $100 to #380 per ton (Mint Beporl, 1883). The Bi;r Blue is almost jieriKMidifiilar, dipping 8SO N., vhieh is anuaoal iu these districts. The vein is oftea very wide, even up to 4 and 5 feet, and consists of white maasive quartz, which besides free gold containa iron pyrites sprinkled throa| it; tellnrides are also reported from the vein (p. 117). The principal ore shoots on the vein dip west and appear to follow the lines of interseotion with the flat veins. A decomposed porphyritic rock found on tlie dump of the Independence is said to come from a dike following the Big Blue for some distance. It is described iu Chapter III, p. 47, and aieara to be lamprophyric dice toA.

The Independence is also a heavy vein, sometimes 2 or 3 feet thick. Aeoording to Mr. Murchie it was at the liue of intersection cut off by the Big Bine, the latter passing through it without fonlting to any ateoti The Lone Star vein can be traced up to the old placer diggings, where it iuteraecta the Alice Belle. Some good ore is reported the latter.

MINKS OF THK LITTLK DEKB OKEKK llASIK.

Grnrnil t'l'ittHren. — Aside from a few veins in the lower part of the biUiiii, there are two centers iu this part of the district where the mtorfly of the veina are elnstared, namely, Canada HUl and Banner Hill. At the former place a large number of smaller veins are contained within the angle of the two strong lissures of the St. Louis and the Orleans (Olencoe) veins. These smaller veins belong to several systems, one striking north and soiitli and dipping west, another with the same strike but dipping east; there are also tlat veins dipping south, and other east-west veins with a steep dip. This great complex lies, as the map shows, near the granodiorite-slate contact, but the veins show no relation to the latter, frequently crossing,' it without being disturbed. Farther, though individual veins show the greatest divergence as to

192 Veins Of Nevada City And Grass Valley.

tlicir coiitfiits add Viiliic. lui iiilliu'iicf <iii tlifir cliaiactcr can be attributed tu the diU'ereut runnatioits. lit general, the iniueH iu tlii8 vicinity re ohwacterixed by comparatively low-pride bnllfoii, aboitt 7S0 Une, Bttoh snlpllliretH, aud especially much arsonopyritv and /iix blmide. A stroiip syt'm of shcel inn is dcvi'IojM'd l>:ualk'l ti) tlu' first nun tinned syatein of vein.s; the Hut, lliiu benches ot ranodiorite dipping west are partiealarlywell exposed along the Bnniier I lilt road near Little Deer Cn tlio slicots, from f! inclifs to '2 feet thick, though as a rule parallel, sometimes show slight divergences iu strike and dip. Small quarts Beams are sometimes Men on tbe joints. The Banner Hill group of veins are in the main pat allel fissures with an easterly dip of about 45°; they are partly in the wt'dinientary area, partly in tlni in'i"i<>diorite, without very marked differences in vein filling and value; uh a rule they contain much silver, and also a considerable amount <tfaiilpbnreta. A (if the (>entry rocic is frequently nottoeable the sheets dipping either eiuit or west.

The Caledonia — This vein is traeeable on tbe saribee for several hundred foet on the north of Little Hcer ('i H'k. The strike is a trifio north of ettst, the dip nearly vertical. It is opened by several old shafts and a tunnel from Little Deer Creek, 1,200 feet long, but no work has been done in nn-ent years. The vein is said to bo very wide and to contain low ;,nadt' ore All ahovctlic tunnel level is ont: the ore cousist-s of inusiiive quartz with abundant pyrite. A considerable quantity of water, tasting stroniy of Iron and depositing a brown ocher, issues from the tunnel.

The Kitigabury vexM. — South of the Caledonia, on the north side of Little ]>eer Greek, are two or three strong parallel veins, situated on the Kingsbury location. They have been opened only by short tunnels and prospect shafts; the dip is ahont 80' N., nnd the width of the solid quartz is from 1 to 3 feet. The Alice Belle is po.sMbly an eastern extension of these veins.

The Lincoln vein, just snath of Little Deer Creek, is a parallel vein in which a little work has been dune, aud which iu the mint report ia eredlted with a small prodnctlon Ibr the years 1880 to 1891.

The St. Louis vein. — The remarkably strong and straight fissure of the St. Louis vein can be trace*! for about tiet from the western limit of the Banner Hill sheet, ou McCormick's ground, up to a place where it disappear undv andesitie tneecia. Its dtreoftion is eastnortheast and the diji 70"' to SfP to the north. The ore throii;,'hotit is very low grade, and the developments on it are slight, mainly cuutlued to a ftw tannels. At tbe eastern end Its deeompoeed croppings have been extensively sluiced; on a claim citlled the Santa Rosa a cmsscat is now being driven to intersect the vein, llie Alpine tunnel was drive on this vein a distance of 400 feet iu 1893, starting from the east bank of Little Deer Creek. On the opimsite or Canada Hill side, there is alao a tminel it several hundred ftet long and serving as drain

BANNER niLL DISTRICT.

tunnel for tin- ( 'liaronniit iiiino. Tlie width of the vein is piven as up to I'J feet, but tlii8 doubtless includes the ultvrcd cuuutry rock. In tbe Alpine tunnel good expomres were noted. For the flnt 150 feet the graiuHliorite. is much dei-omjiosed ; farther in the quart/, vein is from 1 to 4 feet thick and charged with a small quantity of pyrile and cincblende; both walls are well defined and consist of Rontcwhat decomjjosed jjranodiorite. A dike of extremely decomposed diurite iwrphyrite (a fordoscriittion, see j>. 47) l' to ."{fet'twido appears in the hanging wall, 3iK> feet in, and forms tbe sharply deliued wall of tbe 2-root vein of mlid qnarUs. New the breaat a seam was observed, west and parallel tu the slicetiii' previunsly ; it cut across tbe quart/, vein and showed a hurizoutal striation. Toward tbe west tbe vein siilits up into three or four parts, and is wdl ezpoeed on B. Sbiuiie's and McCornuck's {;roandt where the shallow covering <rf rich allnvinin luvs been sluiced otV.

The UliHvw iii acie {Orleam) vein, — This vein, one of the longest in fhe district, being traceable ibr nearly 3 miles, has been known since the earliest times of miniii}? in tins vicinity, but can show no piodnct commensurate with its size, although it has been worked at several places. The strike is remarkably constant, being a little north of west. Tlie dip is equally sn. being 70' to S. The vein fhronghont is in flate, which near the granite contact Vecome8 more crystalline and schistose, and it cuts distinctly the dip of tbe scbistosity. it lirst appears on the Hayflower ground, where it is caUed the Alaska and is opened by small shafts, showing some good ([uartz heavily charged with sulphurets. Continuing westward, it is known as the Glencoe on B. Sharpe's ground. Here it is developed by a 98-fbotdeep short and a drain tunnel, abovti which the ore is stoped out. At this pay shoot the vein is stat<-d to be 4 feet thick, contains abundant sulphurets, and is of medium grade. Steps were taken to reopen this mine in ISM, The next claim westward is the (rracie; a S4-foot shaft on this property shows 1 to 2 feetof quartz in a fissured zone 0 to 7 feet title.

The westerly claims on this vein are described on p. 108. Between

the St. Tonis and tbe Glencoe a ]>ertVi-t network of small veins existS| the more iniportimt of which are indicated on the map. South of the Glencoe are the Hick.ton veins, opened by small shafts and n short tnnnel,and said to have yielded some rich ore. Mr. Shar|)e states that there are three veins within ")() l'e<'t, the outer two dip]>in;,' toward the one in the middle, which is perpendicular. The Enterprise contains low-grade ore, and has not been worked since 18S9.

To the north of the (Ilencne then' is, among others, a series of very flat veins with a .southerly dip of from to 2U'. It is possible that the diflbrent oroppings may represent one and the same vein, continuous from McCormick's ground to the Maytlower at Canada Hill. On the east the Hat vein was found by Mr. McCkirmick in sluicing and 17 (i£oL, I'T 2 13

194 OOLD-iUAfiTZ VEINS OF NEVADA CITY AMD 0RA8S VALLBT.

bydniiilickiii); tlio shallow placers and deoompOBfld rock on the slope ou both 8ide8 of the Gracie vein. It is hflre in alate, narrow, but nob, and sometimes so flat as to be almost horisontal. In one place it even made a roll, ho that part of it iu-totally dipited north. It is stated to have JoiiumI tlie flra< it' vein without (tutfiiifj the latter. AnotlKT flat ledge is fuuud in ou bhurpe's ground near the contact and to the east of the Banner Hill road, and, Anally, similar veins an strongly developed on the Mayflower ground.

At least eight well-deflned veins are fimnd on the Mayflower proper

SOatil of ('anada Hill. Tlie mure inipmtant veins Wi ic at( over twenty-live years ago, but until ten years ago had not worked except BU[>erflcially. A mill omshed rook from the Beckman vein in 1K!).'{, but in 1895 a new 20-Btamp mill was erect <l. The <icvel<)i>!neiif s in ISJC? consist*-*! of an incliBe and several tunnels thu Ueeknian and thu Maytlower veins. The lieckiitau ha8 been worked . fin* 1,600 feet along 'tlie croppings and dtiO feet along the dip, bnt the grejitrst (lepth attained is only 7r> feet. On tlie (Iraiit a 30U-foot iiirliMe has been sunk. The eouutry rock throughout is a black, very impei lei tly schistose ar'illitc, {grading into homfels near the contact. Only the Grant vein cuts across the contact into the prancxliorite. Strong jointiu); is 8hown at the Beckniaii incline, one system dipping 60° west, while the >ther dips 30° to the east. The three perpeodientor east-weat veins, tlie Butterfly, Korth Btar,

ami lUiie. wliile sfronj and well deliru'd. carry low <,'raile ore and have tweu but little exploited, and the 8aaie is true of the Floyd vein. The Grant vein is more pcodnctive and contains near the contact, as well ii northward in the adjoining Canada Hill n-mind, mina good pay shoots; .1.1 tjns, avernring flO. were extra ted from the (iraiit by the owners of the Canada Elill or Charouuat vein between 1879 and 1887. The vein is narrow and contains very mnch arsenopyrite,

besides ])yrite. zincblende, ;ralena, ami some eoarse free

Thu Ueekiuau, with which the Maytlower vein found higher up on the hill nay be identical, is the most important vein in the eomplez. It dtps very gently sotith, being at times flat, or even rolling over with a northerly dip. The vein is .seldom over 12 inches wide aud the walls are very in defined and irregular, the argillite being bleached and filled with calcit*', pyrite, and arsenopyrite next to the vein. The ore conhists of tlic usual ina,ssivo (|uarfz with an often considerable amount of zincblende, giUena, ursenopyrite, and pyrite. The oro is often high grade, and the free gold onasoally coarse, being frequently visible in small itartieles in (|uartz, galena, OT sincblende. The goldia worth 15 iier ounce, or T/iO line.

Faults in the Maj/Jlotcer omphxTtM Butterfly, Xorth Star, and Big Blue— that is, the perpendicular east-west vsinsistlnctly fault the

Bann£E Hill Distbigt.

n.tt.-TactlMi

Floyd and the Mayflower. Noni' of the interstMJtiona hing visible at the time of my visit, 1 rely upon the atatemeuts of .Mr. W. li. Martin, for many yens owner iwd superintendent of the property. The rel*- tion of the east-west reiiiH to the Beckman is shown by the diagram, fig. 13. indicating a rtdative dow nward movement of iH'rhaps 20 feet of the sheeUi between the Big Blue aud the .North iStar. A horizoutal of tho Fkqrd and the two t'anltiiig veins showH the relation tndieated in fig. 14, the amount of the faults not exceeding 20 feet.

The Canada Hill vein was worked from 1854 to 1863, bat the meet extensive work on it wa.s done between 1879 and I s.ST.iii wliieb the mine produced 19,810 tons of ore, coutaining about 4ll8 per ton; the exact peroentoieof inlidmietswii828,Terafing $90 perton. Theore yielded J. so ])er ton in amalgamated gold containing 7.3 per cent of gold and 27 per ceutof Mlver, uud '6.:iO per ton iu couceutrated solphuret probably containing maeh silver. The Oanada Hill indine

is 1,300 feet <leepon the vein and there ax60verO,OCM) feetof drifts; theeountry roclc is a normal grauodiorite. The vein strikes north and aonth, bending to the northwest north of tlio shaft, aud dips 15 to 2U" W. ; iu places it is almost horizontal. It is 15 to 18 iuehe.s wide, frequently, however, closing down to a seam. The ore contains, like the Grant, besides free gold, mnch arsenopyrite, zincblende, galena, and pyrite, and is ribboned by alteruuting streuku of sulphurets. Near the cross veins this snipbnreted ore 18 said to eliaiige to a more qnartzose character, with occatiioual rich bonehea at the Interseetton. An an alysis of the ore .showed th*- presence of telluriam (Mint Kejwrt, 1882).

Faults on the vein. — Tliough at present tlie underground workings are inaccessible, trustworthy iuformatiou iu regard to the well-deilued flaolts on this vein was obtained from Mr. Oharonnat, and his infomation is varillad hy tlie ondeiroond maps and by inspection of the

196 0OLl>-(UAHT2 VEINS OF NEVADA CITY AND GRASS VALLEY.

cross-seaina on the surface. Tlic Canada Ilill if rrossfd by the bcuvy St. Louis vein, as well as by a great nomber of other fissures, rarely nanjing qnartz, striking a little north of ast and perpendicular or dipping slightly north. All these throw the Canada Hill vein to the left, (finn north on the vein. The greatest fault is that produced by the St. Louis, which amonnts to 150 feet on the surface and in the drain tunnel, measured in a horizontal direction, which to a vertiriil displaeeineiit of 45 feet. I'etween llie St. Xfin and the shaft there are at least two and probably more faults, tLirowiug the Canada Hill an BggregBia amount of about 180 feet in Iwrizontal die* tance; the vein is often cut off as w ith a knife, as is shown by a iKii tion of the ma]) of the mine given in fig. 16. The rule for finding the faulted vein in the Canada Hill mine is, dearly, to drift in the hanging wall when going north on the vein.

The Grofif rein, ]>:ir:ill<"l to the <'iuiuda Hill, ]ut east, apparently not faulted to uny notable extent by these ci'oss veins.

Oomparlng the data the Mayflower and Canada Hill veins, it is

dear that the only movement on the faulting veins whidi can these facts is a relative downthrow of the south side, not vertical, however, bat inclined toward the cast at an angle slightly less than the dip of the Floyd and Grant veins. This explains the largo movement on the tint vein dipping west, the sli'lit f lirow of the Floyd, and the fact that no faults are observed on the Grant vein. The rule fur

llndinif the faulted parts of the veins dipping east Is thus to drift in

the foot when going north on the vein. Many of the faulting fissures I are vertical, so that no distinction can be drawn between normal and

reversed faults. The Bl Louis, however, dips about 8.'>° N., and the fimlt produced by it is therefore a reversed or overthrust fault.

Thf Orrenmnn rrhi. a short di.stance west of the Canada Hill, dips to tlie east and, aH-ording to Mr. li. Shariie, interscets the latter without fifculting or being fimlted. Dmay quartz, galena, pyrite, araenopy> rite, blende, and molybdenite were noted on the dump.

Bammrb Hill Dutuot.

Tk0 Wiie We$t to a amall vein paraltol to fhe CNuuidft WXl md

ill T-ittle Deer Creek. It is said to ]k> 1 foot wide and to contaiu good quartz, but u heavy iutlux of v&tei xu the shaft stopped tbe developments.

The Union rein. — a mile eiist of CaiuMla Mill, on the north side of Little Deer Greek, this vein is tlie most westerly of the

Tta. I4t.— Roriaontak] projaetiim, bevlaf fimlto an the Ouads fTftl rrfn.

Bauuer Ilill complex. It was worked rather extensively from to 18G7, and a little work has again been dtme on it recently. It to stated to have yielded some rich hut mostly low-grade ore, the developnu'iits cuii!tiug of inciiue and tunnel from the creek. At a depth of 200 feet on the incline it Is stated to cross, vitbont any change in its general character, from diorite into argOlitO. Thdipto34B. The width is said to be from 1 to 1 feet.

198 Gold-Quaktz Veins Of Nevada City And 0Has8 Valley.

Thf Banner rein. — on tho western slope of "Banner TTill. tliis veiu WivH located iu l.stiO aud worked most actively during the latter part of the seventh and the beginning of the eighth decade, during which time it prodooed several hiindnMl thoiimul dnlhirH. During the year ending Jane 1, 1871, the mine yielded i;i.>,180. In the work was resumed farther north on the vein, and the mint report of 1881 Stated "the incline (north of the old Kbaft), now 280 feet deep, will be 8unk (o a <l'pt h of feet iM'forc <li iftiii} for the old Haniicr slioot." The work wiis discioiitinued two years later, the hoot presaiiiiihly being frand len rich than expected. The old shaft is 970 fiset deep on the incline. Tlie vein, striking north northeast and di])iiiiif; K., is iuclosed iu siliceous ar'illite, similar to that of the Federal Loan, and has great tendency to split up in stringers, on aooonnt of the hard, qdnitery rock. The vein is said to average 4 feet. The ore contains a large percentage of 8ulplmr't<, and great difliciilties were experienced iu milling it. The tailings from the Banner mine were very rich, and an still being woriced by axrastias and other appliances. The pay

little south of the diorite contact. North of the creek it is replaced by fonr yeins, which are worked under the name of Korth Banner, and referred to, going from west toward east, as the Woodville, Dunnington, Tinny, and Ki indoor virus. The first is the ]irin( ipal producer, being credited with llo,0W) in the mint reports for iss'j to They ai'e comprised within adiBtaneeof400flMt, and thedip varies from SOtoiSoB. The WtMKlvilh' is develoiwd by a 1.000 foot long drain tunnel, at the end of which tbei is an uudergronud incline 300 feet long, following the ore shoot down. Hie mine is worked only on a small scale at present. The main tunnel starts iu hard, dark argillite (contact nieta* moriihosed ), but strikes the diorite within 100 feet. The veins are eutirely in diorite. Strong sheeting, dipping west, is developed at the month of the Woodyille tnnnel, whUe an eqmdly strong sheeting, dipping east, shows in the vicinity of the Tinny vein. The Woodville vein shows a decided bend to the west iu its northern end. Tbe veius are very regular, from 1 to 2 feet wide, and are filled with the nsnaJ massive quart/, and SOlpboretS. The country rock is not extensively altered. The veius are comparatively regular, and little of that spUnteriug

shoot w;iR. in the n]>per levels, at leaiit, extremely well defined, 300 to 400 feet wide, and dips IST, tiie plane of the vein. In 1867 the ore was said to average $20 to $30 iej ton, and contained considerable silver.

Flo. 1*. WikkIvHU' vflu. Nurth nnpr mint'.

TkeXorth Banner reint. — The Banner vein can be trsoed for about 1,600 feet to a point a

&#x27;I

BANNER BILL DIOTiUCT.

notieeabto in tbe ftrillite Teiua It to be observed. The sketch (fig. IT) hows the Woodville at a place where it haa .split into two voius. The ore sometimes contains as hipb as por rent of siilplinrcts.' consisting of pyrites, galcua, inolyLxlenitti, uixl totniliedite,' uud is characterized by a Temarkably high percentage of silrer. The repMted prodaot of mm was $4S,in<> in and $2..W> in silvor. or 2,1.10 onncts and 1,780 oauceg silver. The ore yields per ton bj amalianiation. and almoat an eqnal amount in snlphnreto, the latter containiup: about $160 perton, one half toto-third.t in vultii' being goM, rpniaindci' silver. The pay shout on tho Yoodvillt thoniih somewhat iiro;riilar. has Ml extent of 'UH) feet, uud dips to the north on the plane of the vein.

There are several olainis to the eant of the North Banner, located on parallel and similar veins, but very litth> work has been dune on them. Kear the tup uf Banner Hill, in breuciated argillite,are the Tiptop aud PeeriMS veins, strilcinK N. 30° W. and dipping 60° E. The developmentaconsist only of small inclines aud tnnnels. Some rich specimens were extracted from tlie decomposed qimrtz of the Peerless in 1803. In the uoutinuatiou of these veins southward is the old ISritish Americ;i, said to have yielded some low-grade ore. The whi weat aide of Banner HiU is apparently traversed by a ayatem of parallel fraotnres dipping east

The Grand Central rein lies in the conttnoalion of this belt jnat outside of the limits of the map, 3,300 feet fhttn the sontheaAtem corner, the country rock bi-ing black slate. This vein xrm worked for silver long ago, but without much success, and pyrargyrite, in fact> occurs on it. In the same vicinity are several other qnartss vdns, from w) icli trold quartz is Said to have been eztmoted to the valneof several thousand dollars.*

Chaptbe .Xv.

DBTAHiBD DE8CBIFTION8-(OOiminjBD). NBVAOA CITY DISTRICT.

Tbe prodnotfve Teins in tbis district an, on th6 whole, concentrated

in thi* vicinity of the contact of the jrraiiodinrito witli the nit'tiiiiKirpliicbte, though only a lew of theui occur ou the contact. Tiiere an many strong and persistent YeniB among tbeui, frequently wide and heavily charged with aulphurets. On the whole they contain less silver than the Banner Hill and Willow Valley veins, but more than the Grass Valley veins. The principal vein8 to two 8y8tem — (1) the west-northwest to east-southeast veins, with a ste soatherly or northerly dip, aud {'2) the north to-Konth veins witli a nuMliuni easterly dipi The former system is represented by the strong aud coutiuuuus Orleans mine, and in the northern part of the sheet by ihia Sargent ft Jacobs, on whi(;h but little work has been done. The second, to which most of the prodiu tive iiniie-i belong, consists of a nninher of strong vein.H, apparently riuliatiug iroui a point in the vicinity ot Tywu Talk la dlrwtiMU ranging ftom nertli-Dorthweat to north-northeast. The IVovideuce-Champion complex t tiibraees the largest veins in the whole region here discussed, aud the considerable I'aulting which has taken plaoe along it renders it of especial interest. Contrasting with these wide veins and broad faulted zones are the narrow :uul clear-cut lissures of the Monntaineer and the veins in Nevada City. The intimate connection of the two principal systems referred to above is emphasized by the sadden bend of the Ural vein, changing from a northnorthwest to a west northwest direction, and by the less einidiasi/ed bend of the Merritield vein. North-south veins dii>[ing west are rare and are only represented by the Sneath ft Olay and the Mohawk. The otteiisive seam belt west of the Piovidenoe-Ohampion system forms an essex'ially interesting feature.

A few scattered veins occur in the diorite area about Stocking and Pleasant flats. On one of them, just north of Stocking Flat, a small l);iy slioot. eoiitaiiiing about A 1, 000, is said to have been found. The veins occur in grauodiorite, diorite, sodtmeutary siliceous slates, iiorphyrite, and amphibolite, without great diranoes in the composition of the filling. None have, however, been found in the serpentine. The veins of the Providence-Champion system carry the largest amount of sulpburcts, but all of the veins contain in the pay shoots a relatively abundant quanti of free gold.

Nevada Citt Dutbict.

The sheeting of the country roy k is uut piuiuiueut, except in the inindit6 vicinity of some of the larger veins and along the seam belt.

At tlic latter yhwo it very well tlt'tiiicrl. and the Joints dij) to the west. Outside of the liiuitii ot° the sheet the iiorthwent of Coau'a mine tliere is a series of veins, not eontinnons, liowever, and not located on any cotitivct. Among these are the Oro Fino, Ydlow Diamond, Etna, nnd others.

The veiuH of Gold Flut will be deiM:ribe4l (ir8t, then those of Nevada Oity, hMtly the Providenoe-Champion system and the seam belt.

The Orlennit rein. — Forming the continuation of the (llt'iicoi fdracie) vein iu the Banner Hill district, the Orleans ran be traced for miles weet of the eastern boundary of the Nevada City sheet. The vein has been u very small producer, no important pay shoots having thus far been found. Tht; developments are also slight. The Orleans tunnel is driven on it a short distance east of where the vein crosses the rsilroady and the Orleans shaft, 200 feet deep, is sunk 000 feet east of the Grass Valley At the upper Grass VaUey road the Fortuna mine i.s located, with a stiaft 250 feet deep. The vein show.s here several feet of low-grade quarts oontalning considerable solphnrets. Hie Live Yankee is a stringer south of f lie Fortunji, and conne< ted with the main vein. No work was done on tlus property iu 1803. fear its western end the vein has been opened by several sliafbs sontli of the Crosby shaft on tlie Providence vein, and a crosscut from the first level of the latter fotiiid tln' Fortiina .500 feet sontliward. Tlie vein lie.s nearly the entire distuuce iu siliceous clay-slate, gi*adiug over into micaoeons schists near the granodiorite contact. The strike is alioat y. 7()~ W. and the dip constant 70 to S. Only at tlir exti-ems western end does it enter the iwrphyrite area. It is not., us is frequently asserted, a contact vein. With the present developments the opportunities to study tids interesting vein are not good. Hore extensive prospecting might well devolo)) good ore on it.

The MtinluittaH is a short vein parallel to the Orleans and near the eastern edge of the area shown on tlie Nevada Oity sheet. A statement in Ifayniond's !'e]>ort, 1871, page 1.', gives the thickness of the vein as 2 feet, and mentions that it showed plentifully in gold and snlphnrets. It has not been worked in recent years.

The Morn ill ;i star and the Kurcln reins. — North of the Orleans vein and Just east of the railroad the contsvct of granodiorit<; and slate is cut by a number of short veius, striking north and dipping east from 450 to 700. On the Bareka smne work was dona many years ago, and . a great nunilier of sniitll vertical shafts were snnk to open the vein. The Morning Star was being opened iu 1803 on a small scale by an inclined shaft in the slate, and some good ore is said to have been found.

The Siirafh Claif nnd the rritu. — These two short veins in grauoiliorite are churacteri/.ed by a westerly dii>, unusual in this

202 ooLD-QUASTz vKtm OF iriTADA crrr aivd orasb tallvt.

vioiuity. Tlie Sneath & Clay is located a mile south of 2evada City, Just CMt of the flnt raQroMl cunre. Dlflcovetvd in 1863 by means of fhe rich qnartz found in the placers Just bolow it, it wn.s worked quite exti'iiKively up to 1805, producing almut and kidding ore from to $18() per ton. From l&i to 1867 it was also votlcod, ytotding a fiUr profit, the rock at timee containing $40 per ton. Soon nftiTwanl it was shut down, and has remained so sim-e thon. The vein has a tiat westerly dip of 23°, and the incline is run 400 feet down along the ledge. The vein is Irregnlar in size, but averagefl something over a Ibot in width. The pay shoots are evidently snudl,

rw. U.— Tartleal aaetfaii aloBf shaft. Ptiufaarir

but rich; the gold, 82.'t fine. According to T. 11. itolfe, in Bean's Directory i, the pay shoot In the upper levels is 150 feet in length,

contracting below ti 100 f'ft The Mohawk vein, lo<-ated half a mile Houthwet of the & Clay, was also worked during the sixth decade and opened by a vertiral

shaft IIS feet deep. At least oOO tons of ore wt-re taken out, avcrafring jwr ton. The vein appears to contain rich poi-kets of free gold, in which many fine specimens have been found. These note.-* are chictly from Hcan's Directory.

The Pittfihur;/ I Wif/ldnii) This vein Wiis discovered iti IS,")! and

worked at intervals with indifferent success till 18U2; in this year it

prodni'oil >l',noo. -ritli an avora'O of 823 per tnn. From to IST'i the mine iiroducd largely, $1U2,0UU being the yield of the ore averaniig |00, and #150,000 the yMd of the year ending June, 1870. Til (1h' liist twenty years the mine lias hei n um kcd intermittently; in 18i);t vroA confined to the fourth and tlftli levels south of the shaft. A good on the property by Mr. .J. D. Hsigue is found in Raymond'a fourth annual The depth of the main shaft was at t1i:it firnc 'IT'Ji 7H.'? fccf (Hi the iiicliiic.

i'resent develupiueut cuuiiiit of an incline shaft with a dip of 43 and a lenb of 1,000 feet, and an old ineline shaft 600 feet long and 400 feet to the south Of the main shaft. The drifts of the upper eij,'ht levels are extended from 400 to <MX) feet north and south of the shaft ; from the lowest two levels the drifts have been mn for only a short distance. There is a lO-stamp mill on the

The country k is :i dark prct-ii. liard diabase, the aii{;ite largely converted into hornblende. The croppings uf the vein are obscured by the decomposed snrfhee rook ; the strike of the vein N. 48f> and the diji 43- Sl. with many minor varialioiis (fig. IS). The walls are well defined, the foot wall so; the vein is a clean, hard, and compact seam of quartz, averaging in tliicknese fimm 12 to 16 inches. Generally the quartz seam fills the entire space lietween the walls, but Ml the jdaees where the walls are farther apart Iho moss between them consists of crushed country ruck impregnated with pyrite and oaleite, through two or three veins of massive quarts are distributed. Such an oceiirrt'iicc is shown by ti'. 10. drawn hy Mr. E. C. Uren, in the now inaccessible ninth level. ])ay is in the quartz, the crashed and altered oonntry rook being very itoor ; '<the free gold everywhere jire.sent in the (piartz is sometimes, though not always, visible. The snliliurets witii which mneli <if flie pold is assoeiafed are genvially pre.Heut, sometimes sparsely distributed in bunches and peeks and in other places forming solid seams several inches in thiek* ness" (llagnci. Pyrite is plentiful; there is also some galena, but only very little blende and chaloopyrite. Arseuopyrite occurs occasionally. The sulphurets are rich, ranging from flOO to $200, and the we is in general high-grade, averaging 3G, the bullion 80ii fine. The wall rock is remarkably hard and fresh, and frequently lies up close to the vein; the eouutry nyck, repliu-ed by pyrite, soridtsi, and eartMmate, is eonftBsd to the crashed rock between the walk. A remarkable fact is tliat all <quart8 in the vein is good ore and goes to the mill. ''The pinches or coutraetions in the vein in the stoped portioDs are seldom more than a few feet in horizontal meaaarement, while the expanded portions of the continuous quartz are very much greater, in one ease over l'(MI feet'' (Hague). The stopes are very extensive, those on the third level reaching 400 feet north of the shaft and feet . sonthwanL While the developments on the lowest IotbIs are small, it

IBMB'nrMitM7.

804 OOLD-QUABTZ VEDIS OP VBVADA OITT AlTD OBA8B TALLBY.

isclear that the pay shoot iu this part of the mine lias contracted aud split in two, one on Mdi tide of the shaft. As a whole, the wide shoot way Ito to dip to the northeast on tlio ])laue of the vein.

The developments to the southwest have generally stopped when a series of flssares fimltiDg the vein was encountered, but, as shown by the work of the last few years on the fifth level, ore occurs in and beyond the ianlta. The halting Assniea strike east-west, ate nearly

Fill. IS—SmHsii sf inttobnrg raiii.BtaiUi toral.

pciTioiulicnlar. aii'l cniitaifi no ipiarr/: at least three tlu'in have lipcn recognized, and llaue niuution8 that the vein south of the old shaft down to the fourth level has been traced through three of these flkults and appears to he somewhat enricliHl by tlicni. Below the fifth level the vein has not yet been followed through the laultii. The same iissures we found to fimlt the adioining Gold Flat vein. The throw oi the flwlts measnred along the drifts does not esoeed 40 fieet, the north

Nevada City Distkict.

Bide genenilly showing a relative downthrow; tliat is, the vein will be found by dnftiDg to tbu left along tiie fault. The faulting plane is aometimm seen to carve aroand slightly vhea the vin is reaelied,

altl!oii;,'1i on tho whole follow iiii; its course without In one instance on the third level the vein is bent over, following the fault for ft few fiaet.

The Oold Flat or Fetoti nhi.— Located 1,000 feet wt st of the Pittsburg, this TOin has been at the southern end by the Putosi shai't, 400 feet deei along the incline, sunk about 18C5, and 790 feet Bortli of this by the Qold Fiat shaft, 300 feet deep, on wliioh work

was bcinj; jjrosecufed in ISiK! and is;t4. Tlicre is a 10 stump mill on the property. The vein is inclosed in hard uralitized diabase or porptayritic diabase, strikes a little east of north, and east at an average angle of 38'', It is somewhat irregular in direction and dip, as well as in thickness, the latter i-anging from a mere seam up to 18 inches. The sulphurets arc not very abundant and consist chiefly of iron pyrites and a little galena; the gold is 816 fine. There are two ore shoots on the vein; one. about 75 feet wide, bojiins at the (Jold Flat shaft and dips south on the plane of the vein, contrary to the general rule, while the other begins at the Potest shaft, is 425 feet wide, and dips to the north. It is exictwl that the pay shoots will unite in In 1S93 ore was extracted from the shoot in the vicinity of the I'otosi shaft reached by a drift on the 212-foot level of the Gold Flat shaft. At least two baiTen fissures (cro.sings) fault the veiiif one on each side of the Potosi sliatl. They strike east-west, and are or incline slightly north or south. In the lure southerly of the two faults the vein was seen to be cnt oif as with a kniib by the smooth, glistening seam of the fanlting (issure. Tlio throw, measured along tin-drift, is from 10 to 2U feet, and to straighten the fiuilt it is necessary to drift to the left along the crossing; this corresponds to a downthrow of the iiortlicrn

Tfn Mdhlij'iii n in. — A few hninlred teet northwest of the Gold Flat, and between that mine and the Thomas, is the east-west vein of the above name. It dips 38 8., and would seem to correspond to the tint east west veins on the Mayflower, Sharpe, and properties. The Muhigau shows an average width of 1 loot and has beeu worked for a distance of 800 feet along the cropping, but to no great depth, the shaft being 160 feet deep. The ore is said to have aver aped .*.'iO per ton.

The Mertimac rein. — about '2 miles souili of City, on the south slope of the Town Talk Bidge, this short Tein shows the

SKimewhat uiinsnal dip of tL' N. It o])ened by a shafT 3.S.~> feet deep on the incline. Tlic drifts extend chietly eastward from lUO to 300 feet The vein tics iu the black, taflTaceons Mariposa slates, and cuts their strike and dip. It is said to be from 18 inches to feet wide and to coataiu a pay shoot 300 feet long. The ore is banded quarts,

206 OOLD-QUASTZ VEmS OF HBTADA CITY AND ORA88 TALLKT.

coiitaiuiug galeua, besides Iree gold, 817 Que. These notes are t'roiu tlte Elevflfith Annual Report of the State Mineralosrtst, the mine not being

worked diiriiir and ISOl. Tlic small hydraulic ])\t near the mine waa excavated to woaU the deuotnpotied croppiugs of this vein below tbe anderrfte.

The Thomas and Grant rcinH. — It has already been stated tliat tbe priiiciiial vt'iiiH crossing Det'r ("reok and dipping east coiivprge toward a center in the vicinity uf Town Talk. All of tbeiu appear, however, to die oot before reaching the Fortnna oroas vein, and eonth of that there are *iiily tvn vi ins wliii h roprcsfnt the Deer Creek vein systoin. On one of thcui, the Tbuuiaa veiu, striking uorth-northeast and dipping tfo E., periiendicnlar and inclined ahafts have been annk to a deiith of 800 feet on tbe incline. The ore bodies are Naid to he very irregular, from a fVw feet to I">0 feet in width. The ore is heavily vhurcil with sulphuretH and lixHueatly very rich. JSo work hai been done on the property for a long time.

The <;raiit vein, lunch (if'Towii Talk, has lieeii o]>enedby tuuuel. iu itn 6uutberu part, chilled El Capitau, cousiderable capital was expended about 1880, iritbont returns. This vein uiigbt, from ita position, be considered as the sonthem oontinnattou of tbe Merrifleld.

The EatjU' rein, — This is a short vein cropping near the comet*>ry south of Deer Creek, half a mile east of the bridge. It is opened by a fbot-Iong tunnel from Deer Greek, is said to be 8 indies tride, and contains some higfa*gnide ore. In 1881 the vein vas worked to some extent.

Parallel to thb are the three larger veins deecribed immediately below. They may be charat-terizeii as sharp, clear-cut, Ringle fissures, narrow but rich in free gold, and incased in very hard granodiorite, and may be referred to as tbe city veins, because outcropping within tbe limits of the city.

The Xerada Count}/ (/taliott) rem. — This vein, i at several places on Piety Hill, croasea Deer Creek at the su.spensiou bridge and, continuing under the oentw of the city, splits into two branchea. It was discovered in 18CG, but has not been worked for many years past. The main shaft near the bridge is '230 feet deep on tbe incline, but no levels are turned below 200 feet. The lirst level extends 7U0 feet north and fiO foet southi the second level, 200 foet north and 500 south. There is a main slioot at the shaft, and two smaller slioots to the norfli and with of it, all dipping to the north. The dip is li.; tbe width variable, generally narrow, but occasionally up to 2 feet. The ore runs from $20 to A40. A 3 foot-wide barren and perpendicular cross vein faulted the Nevada County vein about GOU feet north of the shaft, the throw being G feet. At this crossing the ore was very rich, reaching $100 per ton.

Thf Stilt s Uiilnif/ht) rein. — The <untliern jtarl of this vein, known as the Half mde iioase ledge, bus been prospected ail tUoug its course suid

Nevada City District.

opened by aa iadiae shaft. of Der Creek it lias been opened by a tamoA htm Der Greek, and some good ore it mid to luive besa fimnd.

This prominent and rich vein has beu worked by ttte lieward, Califbrnla, Gold Tannd and Pemwylvtuii* mines, tSimg a diatanoe of 7,000 feet

The Revard mine is located at the aoathern end of the-vein, where it is split up into two branches about 180 Cset apart. The lieward shafl located ou the eastern vein, is 200 fbet deep on tbe incline and dipt 33 E. A jiay shoot on fliis vein sfopcd in 18!)4. The vein is very regular and ut° un average thickues of 1 foot of solid quart/.. At the depth attained tlie granodiorite very eoft and deeonipoMd,and most of the sulphnrets are oxidi/ed. As a preliminary to Sinkingf a dtaia tunnel is being driven trum Deer Creek.

The California mine, north of the Beward and on the south side of Deer Creek, was located in 1857 and worlced in a desultory manner until 184M;, when new nnu'liinery waa erected; the mine nhut down again, however, in 1868. It was exploited again about 1875, for which year it is credited in Baymond's Report with a prodnetion of 090,000; for many years jmst it 1ki-< been idle. Tlie incline is 510 feet deep along a dip of 'Slit'f and has three levels turned below the drain, which are 200 to 600 feet long. Tbe vein is said to vary from 1 inch to 4 feet in width, the average probably being 1 foot; the ore is reputed to contain about per ton and 3 cent siilphnrets.

The Gobi Tunnel, on the north side of Deer Creek, has the distinction of being the oldest mine in Nevada City, being located in 1850. From 1852 to isr),") it is known to have yielded avcranng m'O jier ton; from 1855 to it was worked continuously, with uukuowu output. In 1888 tbe ore above the tnnnel level was not yet ezbausted. It wa< woikcil innrc oi-less continuously until a short time after lS7o, since which time it has been idle. The vein is opened by a long drain tnnnel from Deer Greek, eonneeting with the old incline halfway up tlie hill and witli tlic new shaft on fop of flic hill. The latter is sunk 3UU feet on the incline below the tunnel, two levels being turned, tbe lowest 330 fleet below tbe drain. There appear to be several pay shoots on the ein. The width of the vein, wlii'i- v ariable, iS said to averafO 1 foot 2 inches, and the ore contains 2 per cent sniphureta.

North of the Gold Tnnnel lies the Bddf datm, reported to have pio> diiced .some ore, and the PenuHiilrania. The latter mine, which hits not been worked for many years, lies northwest of Nevada City, and its shaft is started in the Neocene gravels covering the vda. Aeeording to a report in the possession of the ('iti/eiis' liank, the Shaft Is feet deepou the incline, with drift.s 400 to 500 feet long on each side. The dip is 45'5, with gootl foot wall; the Hizcof the vein, 18 to 24 inches, mostly ribbon rock. About 15.000 tons have been extracted, yielding Si20 in fi-ee gold and 8 per eent sulpburets, tlie latter containing $100 per ton.

THK i.OI.H TfN.Via. KIN.

208 Oold-Quabtz Veins Of Nevada City And Gkas Valley.

THE MOmCTAUfSllt VBIK.

Extend in fT from Doer ("reek at k'ust ."MKM) feet northward, this vein is, in ttie cliaracter of ita fissure, related to the city veins, though its ore is more like tbat of tbe Providence syHtetn. It has been worked extenRively for the last fifteen years, and is cstiniati'd to have produced $1,000,000 ill this tinu*. The trim i]>al 1(>v'1o](iiumi1s arc in t]\r sonfhprit part of the veiu, but it hits been traced over the exHised bed rock of fh hydrftolicdiiflirings, where it shews as Asmall seem, and bends to the north nort Invest, ont branch extrndiii: north northea.st. Some ore as-saying $80 was extracted near tlielare pond in thedigginp, and tbe same vein is shown 4 to 6 inches thick in the Grover and Knickerbocker tunnels.

Tlio Alountaineer mine i; by a tinincl fnmi tli<' north side of Deer Creek. One thousand feet from the monlli a hat't is sunk 850 ftet deep ob tbe Ineline. Seven levels are turned, with a maximnin exteoHion of 1,100 foet to tin-north and G'A) feet to the Ronth. A 20 stamp mill is erected on the projierty. Tbe vein is clear-cut and well defined, with a direction of E., and dips 37j° E. on the

tunnel level. It is inclosed in very laid granodiorite, the fresh rock generally lyin;,' up to tlie vciii. The widtli averages atxuit 1 but is very variable; when it occasionally swells to ',i or 4 feet the ore ngnally beeomes poor. There is no sheeting of the rook a4joining the vein, bnt the forming the filling is frequently ribboned by sheeting and crushing ; much ri te, often also gold, is fonud on the sheeted Iboes. Tlie sheets of (piartz, 1 inch or less thick, often show pro- BOnnced striation, which is jierpcndicular to the strike, or dips .slightly northward. The contains, besides frei pohl, innch sulphnrets, the average being or 4 jter cent, consisting chielty of pyrite, with mneh greenisb-black blende and some ehaloopjrrito and galena. The sulplitu et.s are rich, containiiir from $100 to $'_*00 ]>er ton. No nraeilOpyrite was observed. The ore is chai acteri/ed by a considerable per* centage of silver, and in iaid to average la, the prodocfc of the mine being as follows:

Yxar. GoM. , Silver.

The principal ]Kiy shoot begins at the reservoir on top of the hill and

pitches a little nortli on tbeplaneof the vein. On the firth level the vein liad shut down to a mere seam where the shoot should b*-, but 0|)euel up rich again on the next level below. Beyond this the vein Awka and has not been explored. The third, fourth, and fifth

NETADA Cnr DIOTRICP.

levelH extend 200 feet south of Deer Creek. In the Itaiigiug wiUl, 170 fevt horn the main flwnre, is found a lieavy bat mostly barren vein called

the Black Prince, coniH-cted with the Mountaineer by a cross fixsnre.

Three crosH tissureii, Htrikiug northeast and dipping 2s., cut the ▼eui in the vicinity of the shaft on the tniinel level. They do not carry mach quartz, and are stated to have raultel (he vein I or 2 feet in ome places. The massive quart/., without SUlphuretSi betveeu the pay shoots averages #1.50 or $2 per ton.

TRB NBRBinBLO Va.

TliP lerrifield vein flulonjcst one in tlic district, ancT forms, with the adjoining Ural vein, one of the most iniiKirtant vein systems of the district The Providence, MerrlAeld, Spanish, and Mount Auburn mines are located on it, and there cnxi be hardly.auy doubt that it is the same Merritidd v'in whicii enicrpps fmni the volcanic capping on the north side of Cement llill northwest comer of uiap) and eontlnnes down to Htqrto Crossing. In sneli ease the total leagth of the vein would be over 4 miles. The principal developments aiw on both sides of Deer Creek.

l%e ProvUemot mine, on the south dde of Deer Creek, was located early and worried on a small scale between 18G1 and 1807. 'oiisiderable diflicully vas ex]>ei i'iicf'd in treatitij: (lie lii'lily snljdnuetcd ore, Knox pans being uscil to extract the gold from the concentrates. The exploitation of this and adjoining veins on a large and profitable scale really

dates from the time of the introlucti()n of (lie chloriiiation jtrocess. Since 1870, however, the mine has been worked almost continuously, with a short interruption about 1888, and with gratifying snooess. In the last years considerable ore has also U'cn extnicted by the Irovidenoemine from the adjoining Ural vein. The mine is equipped with n 404tamp mill and chlorinatiou works. The total output of the I'rovidenee mine, or, indeed, of any itt the mines on the Merrifleld vein, is

not ac<!iirately known. Tlic Nevada rouiity Minin;: I'eview estimates that the Providence has yielded $.j,(KN},(HM) since its discovery, which ilgnre, however, seems too large. In the mint of 1800 the mine is <-edited with $50,000, but the average output since tiien has doubtle.ss been considerably larger.

The present developments consist of a shaft 1,800 feet on the incline and drifts on the vein aggregating sevenil mile.s. The mine has been underirronnd to sonth of the Crosby shaft, as illustrated on P|. XXI. This plan is not intended to represent the workings, but only so much as may be neoeesary to an understanding of the imiiortant geological features involved.

The Merrifleld vein is notable for its great width, and particularly ibr the great width of crushed material accompanying it. In fact, in this regard the Ural and the Merrifleld stand alone in the districts; everything points to most intense dynamie aotion aloiig these lines, 17 QEOL, PT 2 14

210 GOLD-QUABTZ VEINB OF miVADA CI1T AHD GBA8B TALLBT.

To tbe north of tiu Fmnddeooe mine OAJfarilleld vda lim entirety ia

granodioritc: at tliat niiiie it cuts tlio slate contact obliquely at a sli'lit auglc, evidently following tbe latter on the surface for a few hundred ftt, fhoogh tbe exposnrra are not qnite deouive on account of aarOm decompoRition. Tbe relations of the slate and tbe grauodiorite are particularly interesting in tho Providence mine. The workings are all in grauodiorite. In the drain tunnel, however, about 800 feet from the entrance, the vein eocoonters the contact and follows it as fiur asthelraiii is acressiMc at present. l?otb tbe lianging wall utul tbe foot wall are very much crumbed and but enough is visible to justify tbe assertion that tbe vein follows tbe contact Tbe workings below tbe tunnel are not now accessible, but it is well known that tbe vein for considerable distance below it followed tbe contact. A part of the data represented on the map are furnished by Mr. Thomas, long time the superintendent of the mine and probably better acquainted with tbe old works than anybody else. Now, as far as is known, the veins of the district exhibit the most marked iuditlerence aa to erosaing or following any contacts; it ia flirther known, fitmi examinations covering a large area in the Sierra Nevada, that the contacts of the granitic rock with the .slates eitlier ruu wholly irregularly or — and this very frequently — are vertical. It is very improbable that the contact abould have happened to follow a plane which subsequent forces causcil to be a fault plane. Taken in connection with tho indications of intense crushing along the vein, tbe only rational explanation ia that an overtbmat Ihnlt baa taken place with a relative upwnnl movement along tbe hanging wall, amounting to about 1,4MX) feet measured along the dip of tbe vein. Indeed, if we assume an appro.\imately vei-tical contact and a line of fiasare crossing it at a alight angle, an upward movement of the hanging wall will place a part of the vein on the contact, producing: a contact area VMtxtsauSkj similar with that shown by the wurkingH of the mine.

Tbe vein atrikea about north-soiitb and dips 35° B. on an avemge, ditTerent parts dijiping from liO" to 4")''. Hetwecn the fresh unaltered walls there may sometimes be as much as 20 feet, or even more, of took more or less crushed and divided by uumerona flsanres parallel to the vein. As a rule this " formation is fromC to 10 feet wide, though sometimes th' fresh unaltered rock may Ufsceii elose to the vein. The ([uartz vein proper usually ranges trum G inches to 4 leet in width, in isolated places reaching 10 ftet. This solid, bard, milk-wbite quarts, not mixed witli oiinfiy roi k, ronstitntes the ore. It much sul))hnreta iu ribboned arruncinent, partly due to primary deposition, partly to subsequent shearing. Where tbe width of quartz is extreme tbe ore is usually for instance, on the l,25(-foot level next to the shaft It must iio( imagined tliat the ore follows a well defined plane within tbe crusheil and lissured zone. On the contrary, tbe tuart/. vein tliins out in <HM plane only to appear in another, or tbue maybe two or three

VKVADA cm DIBTBICT.

moreorlesg nearly parallel vetna within thezone. Tteenished gnuodlo* rite is seau in all stages of the ft mere aofteniuK down to a wlieif tln rock iscoiivcrted tn a grayish frrooii schist with smooth, curved cleavage faces, aud all its cuiistitueuts tluttcued aud squeezed. The Iftte, wbraever proMut along the vein, has anffored in a similar niunner, and tliere may somctimea he ctnisidernble difficulty in determining whether a given specimeu is cnisbed slate or grauodiorite. Analyses of these rocks are given on page 149i. The crashed rock IMXttO the vein contains much calcitu by rsplacemetit and as small seaniH; considcrublc pyritc is usually present. This altered and pai'tly replaced wall rock carries a little gold, sometimes ha high as $2 to$3prtoii.

Tlie qnartz contains, on an avemfje, 6 or 7 per ceiit df nliihnrets, consisting chiefly of pyrite, chulcopyrite, ziucbleude, galena, and a very litfie arsenopyrite. The free gold is very rarely visible. The distriha* tion of the solphurets is somewhat irregular, and on the whole there is less of them than in the Ural veiti. 'rdlurides, while occurring on the Ural vein, are not detiuitely kuowu Irom this vein. Molybdenite occurs rather fireqnently, and sometimes in large bonehes, fhongh nsnally not closely associated with the other sulphnrots.

The concentrated sulphnrets are said to asaay from $80 to $225 per toil,' averaging $1.3U, and contain considerably more silver than gold bj weight, the relation being 3.5 ounces of silver to 1 onnce of gold. The gold is rarely visible to the naked eye. In 1890, according to the mint report, the mine produced 2,800 ounces of gold tuid 2,32U ounces of silver, or apptozimately equal quantities by weight

The pay sluxtts on the ProvidenceMcrrificld vein are rather irregular, size aud value of vein often changing, but on the whole it may be said that the moat important shoot Itallows tiie remarkable split of the vein shown in the plate, and dips to the north about 70. The width of tiie fissured Jsone renders frequent cros cutting necessary.

The Merrijield mtiM, now owned by the Champion Company, is on the northward continuation of the Merri&eld Teia. According to Mean's Directory, this mine, formerly called the Soggs or Nevada Company, worked nearly continuously from ISol to 1807, the yield ranging from $40,000 to $70,000 per year. In 1066, 5,000 tons were produced, yielding $42,000 in the mill and $8,000 in sulphurets. The mine was at that time developed by three tunnels, from 2,o00 to 1,800 feet long. Between 1880 and 1884 work was resumed, with varying success. A shaft 000 feet de was sunk opposite the Providence, and the drifts were said to aggregate 8,000 feet. The daily output of ore in 18Sl' is said to have been 5a tous. iSiuce 188-i but little has beeu doue, aud duiing this examination the old works were not accessible. Becently it has been stated that the intention is to reopen the mine. From inlbnnation available it is clear that the vein aud the filling are entirely

212 Gold-Quartz Teihs Op Mbtaoa City Aito Oba88 Tallbt.

iiiiiltir to those of tbe Providence mine. The vein and vein natter am wide, from 3 feet to 10 feot. and averapro feet. Amount of RiilpbnretSf

6 per cent. From the aiToiint it is phiiti that larRC ore )*)!oot8 liare been found in the mine, und it would be strange, couHidering tbe geaenil cbaracter of the vein, if tbeeie fihoots did not continue in depth. North of the Merriliehl mine tlie vein of the Fi:uno nameisbaReo for some distance, though easily traceable on the surface.

The fljm'sA iMtw is located 1 mile north of Deer Greek. Tbe pay shoot at this place has biHMi worlccil in a wniicwliat extensive manner only during the hist few years. Tbe pro£)erty is developed by a sbatt) at present 400 feet deep, and the ore is worked in a lO-stamp mill. The Merrifteld vein appears here with somewhat changed eharacteristiea. It lies in RratuMlifditc. striking north nortlnvest and <li])]>iii{: -t."*" K. The vein is exi-eeUingiy variable in thickness, sometimes swelling to 8 or 0 feet of qaartx, with some interealated nasses of altered ooantrjr ro< k, then again ]>iiicliiiij; to a nicer st'iim. The pranodiorite is crushed near tbe vein, sometime-s scbistuse, and iu some places travei'sed by seams of black clay parallel to the vein, a product of extreme crashing; The altered granodiorite is filled with })yrito to an unusual degree, bat the mass confiiins voiy little gold. In t-vtieme form tlie altt'n-d granodiorite is a soft white rock with a greasy feel, consisting of carbonates, rewdaal qnartz, pyrite in sharp cabes, and seridte in extremely fine and talc like scales. Culcifc oci -ii-; sometimes with quartz as huge cleavage pieces. The ore, which is generally low-grade with occasional very rich banehca, cowdsta of solid qnartx with a moderate amount of pyrite, galenat and sincbleade. Course gold rarely occurs and ribbon qnartz is not often seen. The pay shoot, said to l."iO feet wide pitches north on the plane of the vein at a steep angle.

North of the Spani.th mine the vein fiirks and mn blind on the anrlace for some distance, but there can not be miicli doubt thattllAlfonat Auburn mine represents its continuation northward.

Jlfoant Anfntm mine, — Tbts mine has not been worked fat many years. In the nunt of 1H8I and 18H3 it was said to be working, bnt it must have afterward. The shaft is 400 feet deep on the incline, and various levels run northward. The vein is said to be 18 indhea thick, and strong in snlphareta, the pay shoots being very irregular. Xorth of Monnt Auburn, at Hagon's, the vein sjdits njt into several almost parallel branches. The vein was struck again iu the workings of the old Empire gravel mine.

THK ritAL ANI> WVllMlNCi VKIXS.

The Ural vein can be traced continuously on the surface llrom the Providence mine to the Ohapman ranch, a distance of 7,000 feet, and probably also continuously from there to tlif Coaii mine at the edge of the tract. For a considerable dUtunce north of Deer Creek the veiu follows the contact between granodinrita and dati and ahom

remarkftbletMidemqr to throw <mt parallel strtngem in the latter rook

vitb slightly less dip than the main vein. In the Vrovidcnee groand the vein haa been worked during the last few years by meaiis of croeacut8 from the luaiu shaft ou the Merrifleld veiu. North of the creek the Uml vein has been worked for a long ttme, being known also as the Ni'w Years voiii. Located in ISwl, it was worked tor iitany yoars without much success. Since 1881 the Champiou Cumxauy has developed the vein, with excellent reanlta; a 30-stamp mill and ohlorinatlon works are built ou the property.

In the I'mrhli nce mine the vein has iirodueiMl a large amount Bince 1803. lu the ChampiuM ground the uutiuit has also been large for a number of years, the mint reports crediting that mine with sums

rangin{,' from !!'T7,(MM) to I.'.SJMM) in the years l.SBO to 18!H'. The wliole production of the Ural vein can not be stated with accuracy, but is probably not less than #2,000,OUO.

On the surface the vein first ap]>ear8 near the Providence chlorination works, in slate; crossing the creek, it is next se<'n at and above tlio Champion lioist, here on the contact'. Making a sharp bend to the west, largely eaoaed by the rapidly rising hill it continues north, at first not strictl}' on the contact, for immeiliately to the east there are a couple of hundred feet of very highly contact-metamorphosed slate mixed with graoitio dikes, before the main contact Is reached. Soon, however, the otTten heavy <Toppings lie distinctly on the contact, and continue so at least u]! to the Nevada City southern shaft. Though the surtiice is very much decomposed, the cropping may be traced with oonsiderable acenraoy by aid of the font oats and tnnuels.

The average dtp of the vein is 35° £., and it may be said to vary between 30° and 40. Near the GOO-foot level in the Providence mine

it reiU'hes the contact, and follows it Strictly between that level and the l.'J."K) fcMtt level, the lowest at the time of this examination.' The rich pay slioot between thes(> levels lies along the upraise not far south of the main Providence shaft. Only on the GOO-foot level haa the vein

been followed to the southwanl, and tin-exposure (here ;ire ,)f Tcat interest. The crosscut is in hard, ma.ssive grauodiorite; the veiu lies directly on the contact, with strong evidence of movement and crash* iii>.' of lioth rKrks. Southward, the granite smm leaves the hanging wall and the vein closes down t4> a persistent and distinct seam. The drift is now in a hard, massive, dark rock, containing occasional small granodiorite dikes; this roi Is a considerably deconposed diabase containing calcife ami pyrite, and is evidently a within the slate, which does not show ou the surface. Six hundred feet from the crosscut the seam bends around to the eaM and becomes very nnch 1 ss distiDot at the end of tlie drift, which is all along in the same diabaslo

In IMBS. n I riM.i'iil niai t>-4 I'rom lltfi l itOO fiMtt Inri'l on Mi n la . in, ii lii il iIm' Crulwdlio bout Um> mae disHUKe tut uu Ike 1.250-fout level. Tbe veUi al tiiin depib >tiU ou tlie vootaoL

214 Gold-Quartz Tbin8 Of 1Tb7Ada Crt Akd Oba88 Tallbt.

dMompoeed rock. Three hundred and fifty feet firom the contact, branch seams start to the eust and west; the one to the east has been followed for almost 1/MHt feet: it soon south aniii and eittots the noriujil siliceous slut e living a pronounced joiutiug dipping west; the seam opens to a well-ded vein with mnch as 16 inches clean quartz, and dips from 20° to B.; no ore shoots have been found on this vfin.

This level has been de.scribd in more detail because it is a remarkable instance of the sudden ending of a Btrong and heavy vein.

Thostronp hftween tin- (>(M) fmit and the l.'jriO-foot levels is about 150 feet wide and dips with the vein. Over this cunsidcrable area the vein is from to 3 feet wide, showinfr only white qnartx mixed with much sulplmn'ts. On iHith sides of this qnart/. lie i to 4 inehos of soft black elay; and in the hanging wall there are usually several liMt of greenish-gray, schistose, and crushed granodiurite iuqiregnated with calcite and pyrite. In the foot wall there are also onlinarily from one to several feet of soft, black, mislicd, shity tnaterial, derived from the somewhat caibunac-eous, contact-metaniorphosed schists. The quartz shows no ocnnb stntctnre, but very olearly a ribbon stmctare chiefly due to deposition of the snlphnrets in large, inegnlar, roughly parallel masses.

The quarts divides easily in plates from 1 to 2 inches wide, and a elose inspection will reveal a slight striation ou these sheets, indicating a sluM'tiiifT of file vein .siibseqneiit to its (le]>osii ion. 8iii;ill fractures, tilled with pyrite, 8onietinies cross the veiu.. The vein iu this pay shoot is clearly and nnqnestionably a once open space filled with qnartz and snlphurots. Near the l,2ri()-faot level the vein throws out flutter stringers in the foot wall, with good ore. The ''slate vein" Ibnnd on the 600-foot level is nndoabtedly a continuation of one of theae stringers. The percentage of snlplnm'ts varies from 5 to 8 per cent: occasionally very heavy masses are found, eontniiiing and above iier ton. Tlie sulphurets found are pyrite iu predominant itnantity, galeaa, xincblende, and ehaloopyrito; there is very little

arsetiopyrite.

A cousiderable mass of altatte, or tellurido of silver and lead, wtis firand in 1804, and was accompanied by free, comtte gold, not otherwise usual in this ore. A little niolylidenite also occurs. Theoonoentrated sulphurets contain more silver than gold, the relation being 3.5 ounces of silver to 1 onnce of gold, but in the whole ontpnt of the mine the gold predominates by weight as well as by value. The gold obtained by nmalpiiiiation is S.'!l' tine. Heavily snipliureted OTO waS fottud to contain 5 ounces of and 1( ounces of silver.

In the Champion mine the character of the ore is very similar to that just described. The sulpliurets average per cent and coiitain from 4 to 7 ounces of gold and 10 to 13 ounces silver per tou.' There are

Nevada Citt Dibtbict.

S15.

Beveral pay shootR of lower grade north of the shaft, and one richer to the south of it; the shoots in general dip north on the vein at steep

aiiplfs. Tlie pfriulp of tlie snliilmrffs ore is about; similar to that jast described. A little luolybdeuitc haa bwu i'uuud iu the vein herealmk

The heaviest body of quartz known in the mine lies in that peculiar sharp bend iu the veia to the Kouth of the shaft. In this place were noted 10 feet of massive quart/., with much sulphurets iu irregular diatribiition, not ribboned.

The rhiimpiiiii mine lieiiijr closed on aeeoimt of legal injuiictiiin during tiie time of tlie cxumiuutiou, the opportunities lor examiualiou were not so good as might have been desired. Along the shaft and in the several levels in the vieinityof tlie sli;ift the I'l al vein certainly lies on the contact between slate and };runodiorite, and it is stated by all conversant with the character of the vein that the whole deposit, us far as known, lies o!i this contact. In s]>eeial cast's it may not always be easy to decide, bnt in {rencral there is nu (liflU nlty in distinguishing the crushed slate from the grauitic material. On the whole, the vein is very mneh like the Merrifleld and the Ural in Providence ground. There is always a ''formation" of crushed, more or less schistose material from 8 to 10 feet thick; the pay — that is, the quartz — may vary from a mere seam u]) to 10 feet in thickness.

A continued strong tendency to throw out branches in the foot-wall slate Tinted in the Ural vein. iinrtli of the creek lies the Wyoming vein, a branch worked many yejirs ago. This vein has a more northwesterly strike than the Ural, dips about 25° E., and distinctly joins the Tral along a line running east-west in horizontal projection. 8ome distance north another " slate vein," also called the 'j'oming, and which may or may not be the same as the one just mentioned, appears, and can be easily traced ui> to a point at the South Nevada City shaft, where it joins tlie main I'lal vein. On this vein, which dips tiatter than the L'ral and will eventually join it, a shaft has been sank to a depth of 900 feet on the ineline; the principal work was done between ISSO and IStM). The vein lies entirely in brownish, somewhat flinty, contact-meta mo slate, often filled with pyrrhotite. The width is irregular, avera;;ing 2 feet; the sulphurets amount to per cent; the pay slionts are very irregular, but a large aOMMUlt of ground on both sides of the shaft has been stoped.

lu the Xrrada City mine {Hold Hill Miuiny Company) the Ural vein has been extensively worked since 1870, and after a short interval of inactivity work has recently been resumed on it with excellent success. The uiiuu is opened near the southern end of the claim by a shaft 1,000 feet deep on the incline; bnt no work is being done at that place at present. The new shaft is located 1. 100 feet nortli iioi thwest of the old one, and is at present 3UU feet deep. IM. XXI hows the extent of the wois. The mine is said to have prodoeed IWOQOO. (STevada County Mining Review.)

216 OOLDKIUABTZ TEim OF NBVADA CITT AND 01U8B YALLBT.

The slate vein and the main Ural vttii, uniting at the southern shaft, eontimM iKMrtliwardj the spoeures ou tbe surface at first being nnsabisfactory: it iH said, bowevwT, that the vein followed the contact Ibr

some distuDce.

Seven hundred lioet north of the fihaft the Tein forks. Ono branch continues northward in the gmiimlioritu and ia known as the Mailer

and Walliu;; a small incline sliuft has beiMi sunk on a branch of this vein a short distance south of the uiaiu road. Though the outcrops are vnaatlsfiMstoryf it Is probable that the Mailer and Walling malceea bend and continues to connect with the mine" indicated on the map, northwest of the Spanish mine.

Another and smaller branch mns ont in the granodiorite, makes a bend, and soon returns to the main vein both on the strike and dip. The main branch also leaves the contact and makes a sharp bend to the northwest, soon changing to west-northwest, and continues running a short distance away ftom the conta(;t and nearly parallel to itk III the old slmft the vein diiis 1'. The kin<,'s arc not accessiblCi hat it is stated on good authority that the whole vein here lies on the contact In the new shaft* beyond the bend the vein dips 20° B., tlic ]art of it bcinfj still llaftcr, for the outcrops lie a blc distance back of the shaft. At the new shaft the vein lies entirely in granodiorite, excejit at one place in a croescat a short distance south of the shaft in the third level, where a projecting mass of fresh, hard, juartzose schist rciKhcs the foot wnll. A sliiir|)ly tlikc of granodiorite is contained in this schist. The hanging and foot walls are generally well developed, the space between them, several ftet

wide, bein<; by a crnsluMl and altered In many parts of the mine there are several seams, accompanied by emshing, back of the front vein. Going sonth in the drain tunnel, one finds the contact between and the schist or slute at the point indicated on the map, at the llrst shoot of the old workings. The further extension was nut accessible at the time of the investigation.

The vein is ordinarily from 1 to 2 feet wide. One body of qnarts, with a width of 12 feet, wius found on tlie (ifth level, very soon, however, shutting down again. Immediately on the foot wall there usually lies a soft clay 1 or 2 inches thick and made up of finely ground np material. The ore is in general a massive quartz, with sulphurets in entirely irrejrular tlistribution. Only rarely is a ribbon structure met vrith. Small druses and vugs with quartz crystals are common. Coarse gold is seldom seen. The fineness of the gold averages 810. Tlie per- 'enta},'e of snljdiurcts, varying! {jrcatly. ntay nvenipc per cent. The suliihurets, consisting of prevailing pyrite with chalcopyrite and less gnlena and blende, are Hob, containing an average of 7.5 ounces of gold and ounces of silver. Hessite or tellnride of silver, and molybdeuite have also Immmi found.

Nearly all of the quarts in the Nevada City mine is ]>ay ore, ranging

VETADA CITT DIBTRtCT.

from $10 to $3U, so tbat tho stopcd areas itructicaily iiuUculc uli iiupurtant qnartx bodies on the vtAn. In tb southern part of the mine these an* four ore slifMt.-< up to feet wide iitid soiiicwlmt to the north on the plume uf the vein. lit the northern pait tho pay shoot liM to the north of the shaft and, though more irregnlar, still shows an indication uf a northward trend.

Beyond the Nevada City the Fral vein can bo followwl jktoss the hill to Chapman's ranch, whore it said tu have l*eeu exposed by a man shaft It is probably eonttnaoas to the Coan mine, where the vein ("irries considerable chalcopyrite, and hns Ix-cii ojiein-d by an iucliued prospect shalt. It here eaters the aplite area and its outcrops are not satisllurtorily exposed.

It is thus certain that a large part of this rein trom the Providence to the Nevada City follows the cDiituct. and it i.s probable, according to the iut'onnation available, that pra<-tically the whole vein between the points indicated ibilowa it. Considering that the whole character of the vein in;licatcs violent disturbance, tho only reasuuaMe exjilaiiation of this fact is tbat au overthrut fault has taken place along tlie vein, rranlting in a displacement of at1ea8tl,300 ftet,measttred along its dip. In other words, the hanging wall has moved up relatively, pushing the granodiorite over the slate and jnoducing a wide /one of crushing and schistosity. This movement has chiedy beencoutined between the Nevada Oiiy mine and tiie Providenec It appears ttiat near the former niinetlie iiii>\ fnient lias been on the branching seams and gradually decreased. A similar distribution of the movement has taken place in the Providence mine, and it is probable tliat the aliarp bend in tlie granodiorite contact between the Providence and Champion is due to movement on one of the cmss seams. Tf is certainly a remarkable tiling to flud a large fault ending so suddenly. The rocks in the anthem part of the Providence ground bear evidence of having been (" a <,'n at wrench. If these coiiclnsiuiis are correct, the Ural vein will soon bu luund to leave the contact and continue in granodiorite, for the fault can hardly have been mnch over l,2001bet. This overthrust movement alnnf; the Merrifleld and tlie I'ral veins has evi* dently, between the Trovidence and tlie Nevada City mine, had tho etl'ect of pushing the contact westward a distance of from 800 to 1,000 feet While it is reasonably certain that an overthnist has ooenmd on both veins, the evidence in the case of the Meirlildd veill ismoveoonclnsive than tbat from the Ural vein.

The first two of these veins lie to the north of ('(tan's .shaft, crossing Kush Creek. Some good ore is rajwrted Iroin a saiull ]iay shoot on the Beven'Siz, while much low-grade ore is said to be ibnnd on John BnlL

A KM) foot tunnel was run on this vein in ISfifi. Tlie Kirkhain has a very unusual northeasterly strike and a northwesterly dip of 00. A

.inns nvtx, Sivsjm'-six, and xirkham vkixs.

218 QOLD-QUARTZ VEIWS OF VEVAXUl. CTTY AKD OBA88 VALLEY.

pay loot was (li8covnU on this vein iu 18U5. The country rock is dtorftet eontaf ning many little pegneatltto dikes. The mine is located

near the lino wlierr that rock changes and more quartzose granodiorito. In Iho pay shoot, wliich appears to about feet long, the vein shows 2 to 3 feet of somewhat dccoinpu.seil quart/, with haps 2 per cent of sulphurcts. The qaartz contains some chah-edonite. The walls lire very distirirf ; few indies of t iny with ]iolislir (l ami stnuted 8urtu4-.e lie8 next to the vein. Oa account deep Kurt'acu decomposition, the Kfarkham can not be traced fhr eonthweBt* bot traces of gold ai e said to be found all through the red soil on the southwest slope of the hill.

TIIK SKAM llf I T.

Fnim iJeer Creek up lowanl iiMiiaa I'hU. TOO to l,ilK) luet to the west of the Ural vein, extends a belt along which the rock— contact-metamorphosed schist. and diorite — is extensively sheeted by S system of Joints generally dijiping west at an augle of 2U or less. This join tin may be seen near the slate ledge in the 600-foot level in the e, and iu theblnff on which the Home shaft is located. At this latter phu e it is very distinct, especially in the schist on the east side. A dike of diabase appears to iia\ e been vaulted by tliese Joints, the hanging wall having moved upward relatively. There is

also a less well indicatcil system of fissures dipping east. Afram, in the hydraulic west of the 2'evada City south shatt, the Jointing is well shown in the iierikendienlar wall of softened micaceous schist, and another system of joints is nearly horizontal.

On these seams a little quartz witli very large amounts of coarse gold is often found. Tiie hill to the west of the Nevada ('ity mine, called Bed Hill, from the deep, red, residual soil covering it. is honeycombed by little shafts and drifts on these little scams. W hile a diji to the west is most common, yet tlat seams or seuus dipping east are also met with. On the west side of the hill, near the contact of ampbibolite and micaceous schist, the surface decomposition is very intense; it takes a practiced eye to follow the seams, scarcely marked in the soft red mtuHs of dccomimsed rock, and often containing concretions of limunite. Along many seams gold is found in largo pie<-es and plates; in 18115 two men are saitl to have ]>nnncil out ft.?.(MK) in ten days from one of tbcseseams. In the above-ntentiuned hydraulic pit aaui:cessful attempt has been made to wash by the hydraulic process the whole deoomposed mass. There is an opinion current that these seams will in depth unite to a larger vein, but no good reasuu can be found to suppwtsach view.

The Slack Lege is a hard bench of luieitceous schist on the westem side of Itcil Hill, carrying a little pyrite, the decomposed cnqqiings of whi< h ar< saidtocontaiuaUttlegold,irobably,however,derivedfiom narrow scams.

The seams are found again on the hill west of the Wyoming mill, and in the continuation of this bdt south of Deer Oreek the Some and

tnnwMBt.l NEVADA CITY DISTRICT. 219

the CadmuM mines are located. In the former several small veius have been find, dipping nortiivest, stmtheast, and east at angles of jNK> to 40°, and Rome of them carrying coarse gold. At flie Cadmas, tlie

works of which were starteiriii 18!t5. there are also spvornl voinR. one of theui up tu 1 foot wide and dipping west. Suuiu coarse gold has been Ibnnd on them.

Tboogh the freat Ural vein ean not be traced nmeh fiuther than to . the limits of the siiccial sheets, there an to the west northwest of the Coaii shaft several veins, usually cast and extending down toward the river. None of them follow the contacts, and, as the sketch, flg. 20, shows, they are ineloaed In different kinds of rodESi The Oro

no. Xap at On FIm ani otkar dahM t mflet wMtanrtfcwert af Vcvada Cttf.

Fino is the most important, and is develoMHl by a shaft 300 feet deefk on the indine. 1%e vein dips from 46° to 32°, and strikes north-north' wcat. TIk' width is said to he about '2\ feet, aiul thoi c are three pay shoots, uue north of the shaft, one at the sliuft and KM) feet wide, and finally one narrow bnt rich shoot south of the shaft. The north part of the vein lies in granodiorite, while at the shaft it is in a granular rock closely allied to a There is a small amount of snlphurcta. The Yellow Diamond has a northwest strike and lies chiefly in amphibolitie schists, with serpentine not Iter away in the foot wall. Several smaller sho itsof ore have IxMMi foiuid on th<' Yellow Diairtdiiil, In one place the vein is cut and faulted by a steep cross fracture, striking I'ast-northeast. The Jnlia is a heavy, perpendicular, thus Ihr barren Tein; it lies in gabbio and curies some copper pyrite. The Fmeat

220 Oold-Quartz Veins Of Nevada City And Gbas8 Vallet.

vein dips steeply to the sotithwest, lies also in palibro. but near the pyroxeoite, aad lias produced some quite bigh grade ore coutaining considenbto aznrite and malachite. The Dement and Btna uee heavy veins, not developed to aoy ezteut, and lie'in diorite or gabbro uear the granwliorite. They also carry elialcopyrite. The Dement can be traced a few huiidrel i'eet beyond the limits of the 8ket4jli,down ou the Steep slope toward the Taba Biver, bat hs not been found as far down as tlie river.

The iUount George lies on the headwaters of the main branch of Bush Oreek, a short distance DOTth of the main road to Newtown, 8 miles out from Nevada Oilgr. It is outside of the special Hlicet.s. On the property is a large vein of low-graxle ore, striking slightly north of east and dipping about 4i2° S. Norti> of the vein, two Hat seams have beeu Ainnd, containing a ferrnginona quarts, dipping in toward the main vein, and some very rich The shafts dcvcloiiinp the property are less than 100 feet deep.' The c-uuutry rock is gabbru, foruiiug the continuation of the Pleasant Flat diorite area.

Chapter Xvi.

DKTAILED DE8CRIFTIOK8-(CONTnmED). ORA8B VALUY DISTRICT.

The TeitM of the Otms Valley distrlet> tboajrh of great mcMj in

dip and strike, show in tlu'ir ores atnl Rtriictiiri' a general similarity. The veiDH are, as a rule, not wide, but the shoots carry high-gradA ore. There is very little Bilver, tbe Omaha system alone otrrying a notable quantity of that metal. Ex'ept in that same system, tiio amount of sulphurets is also below .'i per cent. Pyrite with a little galena, rhalco pyrite, aud ziiieblende form the tsulphurets. Only iu the Osborno Ilill system and in tbe Forest Spring veins is there any considerable qnan tity of arsenopyrite present. Goarse cold is very frequently met vith in the veius.

The Grass Valley veins may be clasiied in seFeral groups or Rystems.

TlIK lUAlKt SVSTKM.

The veins iu this system, ])antllel to the great Orleans veiu of Nevada City, have a strike ranging from east and west to and exist-northejist. The dip is usually steep, and may be either northerly or southerly ; iu certain of t he veins, however, flatter dips are observeil. The veins are often of greater width than those to the south of Grass Valley, and eany bnt a small percentage of snlphnrets.

nut AbPBA, KBHTOOKT, AHA millO HILL VBIK8.

The Alpha and Kentneky are two parallel veins one-lbnrth of a mile

northeast of the Maryland. The developments are slight, eonaistiiig of an incline shaft 300 feet deep; the Hhaft on the Alpha, which is higher up the hill to the west, is 200 feet deep on the incline. The dip is 90 to fiOo to the north,-and the vein strikes west-north west. The veins are in serjientine, Imt a dike of diabase appears near Creek in the haugiug wall of the Kentucky, la liuymoud's IveKirt for 1873 the Kmtncky is credited with a prodnetion of $5,000, the ore averaging $17 per ton.

The Spring Hill vein, about 1,500 feet north of the Miu-ylaud shaft, has been to only a slight extent by two incline;* 'JOO and 300 ftetdeep. It is strong, continuous vein, striking east west, or in the western end west-sonthwest, so that if ext'aided it would intersect tbe Eureka. The dip is GO N. at its eosteru end, chaugiug tu on the samniit of the hilL The vein lies chiefly in serpentine bnt in its

282 GOLD-UABn VSnrS of HSVADA OITT AMD ORAfiS TALLBT.

western part there Is in the foot wall ratlier hmwj dike-like aiaas of

an extremely oliloritic and altered diabase. The Spriii;r TTill is from to 5 feet wide aud coutains a Boiall amount of sulphureU) iu lino diatrilmtiaiii. The ore is generally low-grade; though aeTeral smaller Iota of high-grade ore were milled iu 1870!.* Some work was done on it in 1882 with euoonragiug reaolta.

Tu COB van.

This deposit is oa the west side of the road from Graaa Valley to Nevada City, about one-half mile from the former. It has been idle for many years past, but was exttiUiiiviy worked twenty years ago. It ia to hsTe yielded $500,000. It ia developed by a ahaft 554 fiwt deep on tiieinidine) and three levela ran from tiieaame. TheveiD}

sr.JOHN

aSW. SHAFT. N.N.E

no. SlywilBal HUM UWHghai, JfltaahiA.

which lies in serpentine, can be traced fur only 1,U0U feet west of the road. The strike i.s parallel to that of the Idaho-Maryland, but the dip ia 00° It is not, as oihtu asserted, au extension of the vein just mentioned. The ooteropa are remarkftUy atrtmg, ahowing 8 ftet or more of wdid (juartz. On the west it is said to cnntiiiue up to the St. John, but tliere is not ttoflicieat evidence to aupport this view. 8omo croppings show at the head of the gnleh In which the Goe is located, but it i.s nut beyond doubt the same vein. The ore is said to contain only ! ]>er <-ent of pyrite and 'aleiia. extent of the pay ShOOt iS not known; it is reported to jiitcii the wt st.'

' Eiglith Ann. Stat<- Miu: nli'Ut.

'X<'vad ('ijunty MhiiU;.: ICi s n w .

' Tentli Aim. liepL SUto llasnlugisl.

XBTAOA Cmr DIBICT. 228

TBS AT* jonx mnt.

This property, which lies tliree-fourtbs of u mile north of Gmss Valley, was actively prospected iu 1HU3 aud 1894, but is at present flu.sed down. The geological features shown iu the wurlciugs are of great interest At the point where fhe Aait la aonk some quartz appmni oil the siirfjMU', bnt uo coDttDuous vein conldbetraeed. The shaft goes down to a depth of 220 ftett dipping aoath at 70o, iid from tlicro on to the bottom at a depth of 500 ftet it is nearly perpendicular. Tlie serpentine of the sur- Ihceisfimnd to be

MIklml, IN Dm* Mitrif aloft.

replaced by porphyritp, traversed, by seams of (fig. 21). In tilie bottom of the shaft tbe oontaet with the blade clay-slate WM nnoKpeetedly stmek, end on this oontaet a qnarte vein, in one place nearly 10 feet thick. Drift in eiist the heavy body of quartz soon aud tlie relations at the tare of the drift are illustrated by fig. 22. Between the slate in the foot wall aud the seqientine in the

banging wall lie

Smooth

ft'

feet of

VkkB.— Veto

slaty serpentine with stringers of quartz, the lat- SMAur. ter containing some galena and free gold. West of the shaft the vein, or at least a branch of it,

goes in the clay-slate, but in a little crosscut in the foot wall it shows again the relations illustrated iu Vi. 23, the serpentine resting on the clay-slate and separated from it by a polished seam and a small quartz vein. All these fiMsts point strongly to tbe existence of an overthrust foalt along the contact of slate scrjHjntine. In alonjr crosscut, shown in lig. 21, a number of seams wore met with, almost forming a sheeting of the porphyrite, and most of these earry a little free guM, as shown by proqeeting the emshed matter In the pan.

224 QOLD'uAirrz tsihs of hetada citt and obabb yallbt.

The ore shoot uf tliia iiitvreHtiiig vein liaH been worked iii the Kureka and the Idaho, and la at present exploited in tbe Hafylaod. The Enrt'ka, <ni the western end of the vein, was located in 1851. The vein is intU'i'd here conspicuous lv heavy outcrops on the surface; these outcrops were, however, very and from 1857 to lUdS the ledge was worked only to a depth of 48 ftet, much qnartz, of loir grades being taken Finnlly. in 1H('4, the vertical shaft was sunk to 100 feet and the luaiu ore shoot eucouutered. Ou tbe Eureka ground the ore shoot traa then mcoeaaftally worlced until 1873, when the yield began to decrease, and iu 1877 the mine shut down after vain efforts to find the continuation of the shoot to the west. The adjoining veins of Alobile and Itoannaise were also prospected toward the end, without success. Tbe Eureka mine prodnoed a total of #5,700,000. Several years the mine from lO.OdO to IL'.dOO tOUSOf ore ])er nionfli, niiining from itf23 to $(K) per ton, and averaging #28i, at a cost of mining and milling of $10 to 115 per ton.

Thei Idaho mine, located in ISC't, adjoining the Eureka on the east, was worked but little until 1865; At that time a shaft was started, striking the vein at a depth of 120 feet, but finding no good ore. In 1867 the shaft was annk to 300 Heet, at which depth the great pay shit was found. From 1807 the same shoot was worked continuously until 1894, when the eastern limit of the Idaho ground was reached. The total ontpnt waa 91 1,(38,000, the tenor of the ore ranging from $12. 7G to $.15 ]>er ton, probably averaging $20. The cost of extraction and treatment Wivs from $H to $10. in successive years ranged from a minimum of $1S.'{,4.'>0 in 1871 to $1,010,600 in 1873. From 1889 to 1802 it ranged from $480,000 down to $226,000. The combined prodootion of the Eureka and Idaho ia $17,338,000 in twenty-eight yeai-s.

Dewlojmmta. — Tbe Eureka waa devdoped by a ahaffc which in 1871 had attained a depth of 725 feet on the incline, and which in the last years of was sunk to a depth of 1,200 feet. Below 600 feet, however, no good ore was found. Tbe shaft was ]perpendicular to a depth of 317 feet, and then followed the pitch of the vein. The drifts extended across the width of the claim, a distance of l.."t50 feet. Tlie Idaho is developed by a shaft inclined about 70 from the horizontal, and which attains a perpendienlar depth of 076 feet A short drift extends to the east on that level to the collar of an underproniid incline, running obliquely on tbe plane of the vein at an angle of about 40' from tbe horizontal and attaining a total vertical depth of 2,180 feet, or an elevation of 360 feet the .sea level. From this incline shaft the levels extend eastward to the end of the claim. The Maryland mine is working at pr(\sent on the same pay shoot continuing eastward, using tiieold Idaho shaft for the exitloltation.

Oirtoropf ami eountrjf rodk.— Ike vein first appears in serpentine on

Kbvaoa City Di8Tbict.

the Eonks groand us very strouj; croppinga of whit<>. ina88ive qimrtz. Toward the east, in tli vicinity of tlie old Eureka shaft, indications of a cldoritic decomposed diabase appear in the hanging wall the outcrops are vciy much less prominent, and are not seen at all eaRt of the Idaho-Maryhind shaft. A diabase dike outcrops in Wolf Creek, in serpentine, about where the vein would be At the Idaho haft a coarM'gniined nralite-gabbro appears in the hanging wall, bnt a sliort distance east of tlie sliaft the vein must <inter()] in serjH'ntiiie. It probably continues in serpentine all the way up to beyond the Masliu haft, bnt nntH near that pointno onterope are Tisible; nothing definite

can be seen on the hillside, vhicli is enviTed by dei p, red soil; it is possible that a diabase dike follows the vein here, too. At the Masliu haft, however, the oroppings of white qnartz in serpentine are distinct, and there can be little doubt that these represent tlie vein in question. A short distance beyond the Masliu shaft the line of the vein, if continuing straight, wmdd enter coarse, white gabbro, or it may bend ft little southward and IbUow the line between sarpeatine and gabbxa The old Maryland abaft, 300 feet deep, was sunk southwest of the Masliu shaft to intercept the vein, bot enoonntered nothing! but serjwntine. Three thousand feet southeast of the Maalln shaft the Chevanne shaft is now being sunk iu 'the serpentine to find the continnatioQ of the vein; nothing but serpentine has thus far been met with, at a depth of a few hundred feet. A quarter of a mile fiurther southeast, near the Brnoswlclcniin, the Chevanne tnnnel, 1,200 Itaet long, was driven in a northeasterly direction, but without result; the tonnel is in pabbro and serpentine. Small croppiugs, which may possibly represent the croppiugs of the Idaho-Maryland vein, have been found 050 feet north-northwest of the Chevanne shafl, near the contact of serpentine and gabbro. Underground, the vein lies, in many places at least, on the contact of diabase and serpentine, but sometimes the detcruiiuatiou of formations is not easy without crosscuttiug iu hanging and foot walls. Tlie average strike is N. 77 W.. and the dip iS abOttt 70° 8., occasionally, however, llatteuing out to oO.

In the Enreka groond there are, aecording to Proftesor SflUman, two veins. by a mass or dike of <reeusfotie "'.O feet tliiek. Tlu smaller of these veins, ou the south, has never been worked. The main vein lies, as indicated bj flg. 27,* between a serpentine foot wall and

of esM ud SUsr,

226 Gold-Quartz Vkins Of Nevada City And Grass Valley,

(liko like mass of diabase in tlic liniiRiiip wall. The vein is heavy, varying Irom u few iaohes to 6 feet, aud averaging 3 or 4 feet of BoKd qmvfak. On Ibe a004wtaBdM*-M leireli hi tbeBunkiifthorfteor deoomp— dMNu* vas tMt vlCh, dlvMiof the veto to two, m llfan-

Fia. S5.— CroM Miction of Marj laad Tciu In ttopcs above the l.MO-fuut Icvvl,

tntod in tg. 24.' The dip for tlie flnt 900 feet is 780, which below

decreases to d't' to 70'>. This htirae varies in thickoeH from a few

inches to fVi t . and i.s often filled with qnartz stringers, bo that the whole itxsum may be mined, in a few localities both layers uf quartz

Fn. 20.— (Yom M<!tioo of Marxteod rehi in irtitDM abotre lb Irwl.

come together iu the width of the vein, withoot having the horse he-tween

. In. these OMet there is a line of quarts crjrstals visible which

fill the namnr cavity sometimeB left* On the hanging wall thera is a

OoyM from MelTlUe in UmXIMIi Am. Jtopl. State MlMnhglat.

Gbam Valley District.

distinet obky selvage. the westerD extension. Professor Silliman niakt-s the following statement (Beau's Directory, p. 23): "The Eureka vein, going west, faults in the Wliitiug groaud, aud, bavpiwviooalj become almost tertieal, hu to tbe west of tlie ftnlt nortlu'rly dip.''

lu tlio Idubo aod Maryland miueti tbu vutn is e(|ually well detiiied; tbe dip is Ikem TStoSS 8., end tbe strike very regular; tbe width of the ore — that is, of the qnartz — probably averages feet. The series ofr n well exposed in the foot wall, but tlio diabaae is not always distiuct. Flaky, eUloritic, or seriieutiuoid soft rock, Idled with caleite end cubes of njrrite oAea Ibrms tbe hanging wall; oompftmtively fre.sh jliabasc was uoted at the shaft in the seventh and fifteenth lerels and n Ibw other places. A lotig crosscut, stiurtiug froui the seventh level and extending 800 feet in tbo hanging wall, gina in diabase ; 25 feet from tbe vein eoarse gabbfo begins to appear and continues for 200 feet, mixed with what arepiobablydikesofdiaba.se; then .smitliwaid to tho face the crosscut is diabase, eat by seams in many diraotlons, but not showing any distinct veins or uiiueralization. On the whole, the vein wasvery regular ill width ftnd character; in a few places it showed signs of splitting up, but soon in creased in strength again. Sach places were found iu 1875 below tbe SOO fbot level, when tbe banging wl went down flat and tbe ledge broke up in stringers; a;:ain in lsS2 and 1SS.'l tlic (iri hrcatuo poor on the 1,100-foot level and the vein irregular; some distance eiist of the MaiJland line, on tbe l,500foot level, tbe vein splits in two parts, bnt it baa in every case been found strong and reunited. The vein i.s freqnentiy accompanied in the foot wail by a characteristic gangae of dolomitte rock, sometimes colored green by mariposite, wUdi Is to be regarded as a altere4l serjM'ntine. These and other rocks frolh tbe Idaho- .Maryland arc described in detail in Chapter XL Mr. Attwood states that this dolomite carries a little gold.

228 OOLD-iUAHTZ VEINS OF NEVADA CITY AND GKASS VALLEY.

The ore. — Tlip ore coiisista exclusive<'Iy of the solid quartz in tlie Bbuot, except when the acyoiuiug couutxy rock is impregnated with <inarts Btringera, m sometiiiMS hapiMiis. The ebtof value In the oie ie in tlie fr'(> jxoh\, which aa a rule is in fine distribution. Sometiiufs, however, rich ''specimen rock" is met with ehowiag aboudaut coarse gold. luM varied, as stated, from #60 down to tlO and $13 per ton, bat an vecnce wonid probably be about §20. It would appear as If the western part of the pay shoot were somewhat richer than the extension toward the east. The gold is 818 line; the amount of sulpbureta is small, bavlDg varied from 1( per eent in the Enreiw to three-fbnrtbs of 1 per cent and 2 per cent in tlie Idaho and Maryland. Tlie value of tbe coDceotrated sulpburete is about f 100, sometimes reaching §400. Hie MBoniitof saverintliesalplrareto is maUilwiiigstatedtobiLS

Flo. SR Approslmat* ontlinn of th Ksnltt-UihparahMC 2b hhImMwi an the plan* of tk*

Ttii. OtpoT vafaitvvahl UMobaenrwr.

eents silver to §1 gold. The sulphnrets consist of pyrite, chalcopyrite, and galena, with very little arsenopyritc and hardly any blende. They contain a strong admixture of tellurides, not observed, however, as separate minerals. The sulphnrets are diiUonlt to oonoeDtrate and to

work.

Structure of ore. — Tbe ore is very frequently banded or ribboned. Silliman remarks on this banded stmetnre in -the Bnreka and says tiiat

tlie joint snrfaees are often coated with gold. A banded structure by arrangement of the iiyi'ite iu parallel streaks is also noted. Pis. XI and XII' show the stmetnre of the Maryland vein. In PI. XI the riblmn stnictnic is illastrated, due without much doubt to the sheeting of the vein subsequent to its fiwmation. In Fl. XII the vein consistoof

'FiMiptalognphstur Victor Pwwy, wmtoiMitot of tbt Mtyteia, wbo— notMydMib to im in* taa MSni aUb gf tto tiMdiKww hwgtog vaU in Ua Bin.

Grass Valley District.

solid white quart/ with no indication of ribbouinjj by sheeting or deposition. Fig. 25 shows on smaller scale the locality of which PU XII is a part. Fig. 36 ahowa tbe Btraetme of fhe vein at a plaee in the slope not far distant from tlio (Ifteonth lovel.

Pay thooL — The pay shoot of the Eureka-Idaho vein is one of the most remarkable known in Tetn geology. Ita extent and character are shown iilllg.28. Over the whole shaded area it in safe to say that the veilL averaged 2A feet of solid quartz. Outside of these limit.s the vein grew poor rapidly, and frequeuUy closed down to a were seam. A vein 2 and 8 feet thiok ia, however, fimnd in many plaeea oataide of the pay shoot, ami the pliysieal cliaracteristics of the vein remain the same. Of the eighth level iu the Eureka the snperiuteudeat stated that the walls were good and regular and 4 ftet t, bat the tcId was small and very poor. A small pay shoot was found in the deepest part of the Idaho shaft; it was followed for MToe distauoe, bat eveutiiaUy proved too small for successful exploitation.

13ie principal pay shoot has thus been fonowed for almost a mile with an average dip of K. on the vein and an average Avidtli of fiOO feet. There is no reason why it should not continue for a loug distance eastward, provided the veia does not enter the serpentine; if it does fliat the probability is that tibe wia will be found to split up in stringers. The fact that over a largo area the vein lie.s in the 8er|)entine in the foot wall and lu diabaau iu the hanging wall would lend some strength to the viewtiiata oonriderable ovMrthmst had taken jdaee along it| for eonfaets between different rocks are as a rule far from regular* While this is likely, it can not be said to be proved.

Located 2,000 feet south of the Idaho and parallel with it in strike and dip. this vein is deviIoi)>d by a tanned on the east end and a riiaft 100 feet deep on the WSOt. The vein lies in a |>eculiar mixture of dark* green diabase with coarse nralite-gabbro, in places share4l and serpentinized. the tbrmer probably forming a network of dikes iu the latter. The zone of thermal alteration is wide, as evldeaeed by the bleached country greatly impregiiut<'(I with caleite and pyrite, and sometimes colored green by mariposite; seams with large cleavage pieces of reddish ealcite also oooar. In one case gold haa been noted inclosed in caleite. On the foot wall was a distinct aud riclt stringer quartz with coarse gold, galena, bleudo, and At a deptli of (!() feet this stringer extended out in the hanging wall and splintered uji, the ▼einiets being rioh in eoane gold, while the foot wall eontlnaed down.

To the southeast of the Idaho-Maryland b a group of parallel veina

which evidently to the Idaho system, thonrh the strike has turned uiore northwesterly. The Brauswic-k (also known as the Englisbf or CyOonnor), with a strike of S0 W. and a soathwesterl dip

mr. soi'TH IDAHO vkiv.

raa oaooF or vsun.

230 Gold-Quartz Veins Of Nevada City And Grass Valley.

which down to 400 feet is tbeu 60'=>, and finally at (UK) feet wan located early and has been worked with varying huc8.s for a long tfane) the upper levels oontainiDg amne good ore boots. For the last spvt'ii years the mine has been extensively t<'(l. some good bunches of ore have revetitly been found in the lowest leveL The mine ia developed by a shaft 700 feefe deep on Che incline, and drifts extending 300 feet toward the west. The vein is eontainetl in a chloritic schist derived by (lynanio nietamorpliic proccsHes from a jwrphyritebreccia, and iutersects the strike of the schist at an acute angle. There are usually two well define*! walls, 2 to 4 feet apart. The epoch between tlie walls !s only locally wholly filled with massive quart/, beinj; peneraliy occupied by soft chloritic schists, extensively altered by hydrofliermal iwooesMs; Una acluats are either parallel to the walls or, aa is ItoqiMiidj the case, broken and inegnlar; tlieiy contain streaks and

ramified veins of massive quartz (fig. SB), trhiuh sometimes increase in thickness and oeenpy the whole space between fhewalls. East of the shaft the vein eloiOl down to a mere seam. Free gold is rarely yisiUe in the quartz, and the Mulphnrets,

▼hich generally are rich, consist of pyrite, and galena.

The Oold Point ia a rein parallel witli and 8outh of the Bmnswiek. The heavy 70'' S., ran bo traced for over 2,000 feet. It is by a tunnel irum Wolf Creek connecting witli iucliues t'rum above. To the west of the tunnel the vein is very heavy and eontaina hirfje nia.sses of low -trade ore. The eonntry rock is a schistose parpbyritic breccia, less chloritic, than that of the Brunswick.

The Uniom vein, the of which are visible in places on the north bank ot Wolf Creek, i.s one of the earliest-located veins in Hrass Vallej-, The ore was worked with an arra.stra np to 18.'4. In 18<!."> mill and hoisting works were and the mine was worked with profit until 1870. The total prodoct is given as 2SO,000. FronJaanary Ito AnjTUst 1, ISCn, the mine tons, yielding or about $1U iH-r ton. The vein, which is continued in schistose porphyritic breoein, dips 50° 8. and has been devebpcd by a shaft 268 feet deep on the incline. The width is said to be considerable, averaging feet The extent of the stopee is shown on fig. SO, taken from

Ora8B Tallet Dihtsict.

Baymond'ta Beport for 18tiO-70. The gold is 822 line. Oalena ia said to predominate tn th BulpliaTetiB*

The Cnmhi hlge vein is located on tbe sontli tide of Wolf Creek. The Lacky and tbe Cambridge mineH were on this vein and worked extensively about 1865 to 1868. The Lncky mine, on the went, had a IS-stamp mill and was exploited by a shaft 400 ftet deep on tlio incline, 10.(XiO tons of ore being extracted from 1805 to isr.7. Tlio adjuiuing ou the east, was opened by a shaft 20U feet deep, and a 10-tamp mill was erected on tbe proportgr; 70 tons of oie per week irere crnnhed for a long time, averaging $90per Ion (Bean's Directory]. Hie vein lies in ehloritic schist, di]>R 30° SW., and is generally wide, averaging 2 to 3 feet. According to Professor Sillinian, free gold is tarely visible in the ore. If these are correct, this vein, ns well as tlH< Tnion, may be ittudflied prodootive again. Ibe gold ie ftom 817 to duiO Hue.

Th Francfort vtim, About SOU feet south of the Oambridge, nud to have prodnoed ome good ore Arom tbe oniaga.

ram cMvwi* ronnc rmm,

Tliis deixsslt, locattxl on the south side of Wolf Greek, half a mile east of the center of the city, has been worked at Intervals sinoe 1886. The production is stated to have been tl. (0,000, of wbicb $80,000 was found in one bunch of ore with ninth coarse gold. The ahoA is 400 feet deep on the incline, with levels extending east and west, on!}' the upper two levels being accessible in 18Ui. The vein, which strikes northwest and dips 1V> to 80o N., lies in serpentine or serpentiniMd porphyrites, the width of quartz and vein matter varying ft"oni a few inches to 4 feet. There are considerable amounts of magnesic and calcic carbonates produced ftom the serjientiue by thermal alteration. A thin sheet of quartz, still adhering to tbe foot wall near the shaft in the drift, shows beaatiful polish, with newly horisontal striation; ia

232 GOLD-QUAimS TEim OP NRVADA CITY AND GRASS VALLET.

other places tbe striatiou in the foot wall is parallel with the dip. The aerpentine of the banging vail is iUIed with carbonatea and pjrrito; th6 ore earrit'H fears( gold and jmt cent of Kulplinn-ts.

The New Eareka shaft, 5U0 feet deep, was siiuk about 1888, 9IM) feet northwest of the Grown Point shaft, to And the extension of the Crown Point vein. The Shaft is inclined 80' X. down to 121 feet, and fi-om that depth is vertical. The upper part uf the shaft was in black slate and sandstonck, changing at a depth of ISO feet to chloritiu and serpentinoid rooks derived from porphyrite and diabase Highly mineralised zones, ricli in and with some quartz, were met with at a depth of about feet, but uu well dehned vein.

A 20-foot crosicnt to the north ftom the 200-foot level on the Grown Point has intersected a mineralized zone along a fissure dipping in part north, in part sontb, at steep angles. Along tiiis fissure the country rock is chiefly serpentine, bat black silioeoas slates are also met with, usually highly iiu{>i-egnated with pjrrrhotite. The ore is most nnusnal in character, diflering frreatly fnuii tbe ordinary |uartz veins, and consisting chiefly of calcite, pyrrhotite, chaluupyrite, with some ordinary pyrite; the snlphnrets ooonr as heavy masses 5 to 6 inches thick along tbe vein, and a sjitnple assayed by Prof. Cliarles E. Munroc contained 17.5 ounces of gold ancl 12 ounces of silver per ton, no free gold being visible. Pyrrhotite impregnates the country rock in the vicinity, and slickensides of it are seen along the vein.

Trb Baoobk Hill Vww.

The Badger Hill vein, on the South Fork of Wolf Greek, 2,000 foot SOnthwestof the Crown loint, (lot s not crop plainly on the surfat c; it is said to dip to the north under the railroad; no work has been done on it for a long time. The shaft la said to be fiOO Ibet deep, with extensive drifts; the vein spotted, but in places oanying very rich specimens.

Within this area occupietl by the veins of the Idaliu system there are very few veins with a north-sonth strike. The Morehouse, 2,000 feet -vvcst of tlic Marj'land, dips E. 30; if has not been shown to contain much of value. The Wasbiugtoo vein, 14 miles above the Maryland, on Wolf Greek, haa been opened to a deptJi of about 300 ftet, and is said to show wen in snlphnrets and contaiik 3 to 4 foot of qnarts."*

ram iKrsaua vsiira.

About 2 miles north-northwest of Orass Valley, on both sides of

Deer freak. llicre is a series of stroiifj veins witli a west northwest strike, and closely parallel to the Idaho and Ork-ans veins. The veins are inclosed in gabbro or in serpentine. The principal one is the Imperial, crop])in in light-<'adored OOanW gabbro on tlie north bank of Deer Cieek. Work ou this mine was proaeonted in 1883 and 1884

Oram Valley District.

when a shaft 280 feet deep on the incline was sank and dritta extended Mit nd treat 8S0 ftei. The Tein ia htm 8 to 8 ftetwide, ataowing aome galena and free gold. This vein contuiiMa, with a alightly moie norCbwcaterly atrike, toward Newtown.

TRB YKDfS OF OOU> HILL, XAB8AOHUSETTB HILL, AHD TIOINITY.

The veins in this locality, within tlie city limits of Grass Valley or a short distance to the sonthwest of tliem, were the earliest worked in this district) though but little work has been dune on them in recent years. They ara, in general, characterized by amall width bnt rich ore, with frcqni'iitly coarse gold. Tlic sulphnrcts aro suborrliiKitc both in quantity and quality. The strike is to the north, with variations to the east and weat; the dip at anglea of 20° to 40 either to the east or to the weit. The veins lie either in grauodiorite, porphyrito, or diiv base, the latter two rocks being connected by transition. A Ktrong sheeting of the country rock is sometimes apparent, as, for instance, in the weatera part of Main street, where the Joints of the grauodiorite dip to the west at .30; this is illustrated in PI. III. ji. 104, Near the lioriuier mine, on Wolf Creek, a strung sheeting, dipping 10' E., is developed In tiie diabeae. The flaanrea of the veina are witboat donbi eloflaly related to tliia abeeting and ptodoeed by tiie aame fbroe.

Ths Oolu Bilubockt Bar Vkk.

Located earliest of all veina in this district, this vein has been worked extensively, though to no great deptli. alonf; a distance> <if .1.(H0 feet. The northern jiart has been opened by a number of vertical ahafta to a depth of 100 to 200 fiset. Thia northwn part of the vein was nearly cnntiiiiionsly from 18.50 up to 1807, and is thoulit to have yielded during that time. Between 1890 and 1U3 the mine was opened again the Gohl Hill shaft, 550 feet deep on the incline, the vein 2S° E. Levels are turned at 2!M) and 540 Tfet, the lower extending 350 twt nnrtli and 600 feet aoatii. It is expected that the mine will soon be reopened.

The vein europa in diabaae, bnt all the lower workings are aaid to be in Thi-strike of the vein, tliouu'h very irrepiilar, is north and south, and the dip EL The imrtion, near the crop> pings, is, however, in places mneh flatter, and the whole hill slope is eompletely Imueycombed by drifts and abafta. The Gold Ilill vein is very irre;;ular in widtli, varying from a mere seam nji to 6 feet, the average being said to be 2 feet. At 275 feet south of the shaft the vein is said to have been ont off a faalt flaanre, striking northwest t oTitainiiig no ore. The hanRin;; widl of the Gold Hill is strongly impregnated with pyrite. The vein is characterized by irregular pay ahoots, at plaoea bdng alnioat entirely barren, while in other plaoea large pockets of ooarae gold oecnr.> North of the Gold Hill abaft the

IMmie A.ttw—A, TcaUi Aan.

284 OOLD-QUARTZ VBtlW OF NBTADA CITT AND 0RA8 TALLOT.

vein iti miuI to split, one branch extending uorth aaU tiie otiier north- Mt. It to itnponlbitt to verify tbto at prMent tb oaterops not htAng

re<"<>giii/.abK. Tho pold is from 8.M> to S70 fine.

Tlie jMassacIiutietts Bill vein, worked by tlM aM liooky Bar deep abaft, 18, beyond ranch doubts on tbe same fiasnre as the Gold Hill. It wju* worked with short interruptions between 1850 and 1860. In 1864 and 1865 1,000 tou.s of ore per mouth were extrticted for a long time, and this part of tlie vein is reported to hiive yielded ,000,000, which, if tbe reportii are reliable, would make f 7,000,00 for the whole vein. Tba Rocky liiuhatt was sunk to strike t he and then followetl tbe dip of the latter; a total iwrpendiculiir of 300 feet was attain-d. An agrepato of li miles of drift ;s said to Lave been rnn from tlie shiift. In 1S95, after a long peril of <iuit'>( 'ii( the vein was again opened up by a shaft in the same locality. There is but little information airaflable aa to the character of the ore and pay ahoota. The latter are, however, reported to be more regular than on (lio Gohl Uill vein. The vein crops in diabase, and only that rock has been atmok In tbe deepest workinga, as attested by tbe dmnpa but eTentanj it will be fomid to enter the granodlorlte., Tbe gold is 855 fine.

The two Slinnjrhai veins lie from 200 to 400 feet wPHt of tho Rocky Bar, and have been on-ned by small perpendicular shafts. A consider-

aUeanioiintofiioh ore baa been taken ftomtheoD. Tlie gold is MO line.

TBI BtACK UCDOa.

This vein, tnMsable on the Hurface by shafts and prospect holes, begins a short distance south of tlie Shanghai vciun and dips to the west at angles from 50 . It has been worked only tu a small depth, but is said to bave produced $75,000 in the ciu ly days. Tho Hndqoa Ray shaft was sunk, iu 1802, to a pprpeudicular de[>tli of 1S5 feet to intercept tho vein. At 14U feet two liat stringers were found containing ooarse gold, and at the Junction of these strangers with tbe main vein the (innrtz was also rich. Some of thegoWocenrsas leaves inclosed in a brown opal. The main Ictlge is wavy and irregular in strike; the narrow pay sbooto dip to the aonth on the plane of the vein.

nt* atxaaaiAn mux, toom, amd TwiuofiT enAim.

The Oiuoinuati Hill ia also a parallel vein lyinir half a mila west of the

Gold Hill. It has lxn worked tn a small scale off and on since 18/50 and the priucii*al explorations were made at the north end. The Sootm shaft waa sunk in 1881 on a amall vein to a depth of SQOftet, bnt netting of v;ilnc was found. On the Twilight claim stneral small coins are found, dipping east, parallel to the liocky Bar. Thuiare also iu this Tidnity seyenl veina with a northerly to north*north0SBtorly strlksi and westerly dip.

THK rKABODY VEIW.

, Located just outside the city limits, this vein, whose outcrops can

not now be traced on the snrfhcei has been worked at various tiaiea

e

umomir.l

Grass Valley Dkstkict.

the last time from 180 to 1893. The northern ehntX, which is the deep8t, ha* been sank 4U0 feet on the IneHne; the upper leads are OOnnected with the old Bhaft. The vein, wh'n h (lips33 W., lies partly in gninodiorite, partly in uralitt' (liabase. The width is said to lie 18 inches ou the average. The iiuurtz o( the veiu ooutains extremely heavy and coarse gcAd in inegnlar boots.

Thk .Ikky Hlitb Ani&gt; Iikhmosa Vki.Vs.

These veius, located near the Watt Park, strike to the northeast and dip northwvat at ang lea fton 30f to SB, tbo country rode Mnf aniUt>

dialnise. The latter mine ia opened by u sliaft (KK) feet deep on thd iuuliue. The veiu is aaid to be from 2 to feet iti width, and the qiiarti oontati.8 aonw pyrfte and galena. The woA was cMefly done in 1808. In the following year the nine waa shut down, tbe oce riuoto not having come np to ezpeotationa.

TRs iHKHnak*T'-a*niira aui. vniib

Tliis long vein crnjis in grnnodiorite on tlio east side of Wolf Creek, ohietly within the city limits, and is nearly parallel to the Gold IliU veui, though dipping in an opposite direction. The two veins will clearly iuteraeot at no great depth. At its northerly end the vein forks, the western branch tiiniin north northweat through the city, and is here kuowu as tho hock Koche veiu; it is narrow, but some rich specimens are said to have been fbnnd in the eroppings. Boath of this it i.H known as the and has been worketl at various times. The vein was worked in the early fifties; again in 1863 good ore was taken out; from 1868 to 1873 It was worked with varying success by the Dromedary Companj', which erected immping and hoisting works and a 10 stamp mill. The M-in i-; said to ho from 1 to 1 feet wide, and has lurui.sUed considerable (quantities of ore containing coarse gold and mnniog firom $30 to #60 per ton. Tlie next claim is known as tlie Wyoming, on whirh in rectmt years ashafthaH been sunk 280 feet on the incline and some high-grade ore extracted. The snlphurets are said to be very rich, containing $300 per ton. South of the Wyoming Uievein is known as the OrandaOf and lias been worlced by means of tunnels from Wolf Creek.

of this again is the Granite Ilill mine, in all probability ou the same Tein. The Granite Sill is developed by a shaft 600 feet deep on the incline, with drifts extended on the third and fourth levels to a maximum distiince of feet. Rich ore wius found along the out:rops in ISTiO. In 1870 the mine was worked to some extent, and again o()ened in ]S<.I2 and 1803. The croppings are in granodiorito, but at the third level the vein rnt-< arro'is the contact into diabase witlunit any notalde change. The fourth level is entirely in diabase. A dike of graniteporphyiy waa noted aonth of the abaft on this level. Tbe vein, which dips from 150 to 30O W., la small, sometimes eloaing down to a mere

238 ooLD-QTTAims Tcnra op kevam cttt and ORABB TALLirr.

seam, us iu the tliird and fourtli levels soutb, tlieu again opening up and oontdiiiinff 1 or feet of qnmtK. The fbot wall is wpII deilned, the hanginff being; more irregular. Fresh country rock often comes close to the vein. The ore in the levels was of a generally poor character, but iu the fourth level uorth a pay shoot was struck, running up to a point between the fourth and third leveb. The ore is high-grade, ranging np to $50 per ton. nro very abundant, consisting ebiefljr of pyrite, yellow or bruwu zincbleude, and very little galena. The gold is fteqaently ooane, in leaven and mniwog adhering to the quart/, crystals, nnd often noted to be associated with tlieblcndc. The concentrated sulphurets are not of high grade, containing only about $60 per ton. The quartz is often cry staUized, comb stmcture beiu g very common, and the whole vein sometimes filled with loot bunches of milk-white cry.*it4il.s, orteii laiiiiiting from a fragment of country rock, partly replaced by pyrite. in the more compact parts of the vein dnteen with erystala are of common oocnmoee.

The DrotiHMlary GraniteBUlTeinappeantooontainnKKeaalphttreta than the diabase veins.

THE ROK HILL VRllf.

llieBose Uill vein adjoins the Dromedary on the east, but dips in the opposite dlnctiOD. This vein is reported to have yielded $100,000, and

a fesv years ago $7,000 in was taken out within a small space, liccently t he mine has been reopened. The shaft is 122 feet deep on the ineline. The vein is from 4 to Iff inches wide.

THK VEINS IN TUK VICI.MTY OF NKW VoKK HILL AND NOKTH STAR,

From the Hudson Bay shaft southward for a distance of 3,(MI0 feet the diabase is cut by an extensive system of flat veins. The outcrops fotm wavy, irregular lines, and some of the veins are practically hori* zoiital. In general the strike is east and west and the dip either to the north or, more rarely, toward the south. The veins are narrow, bat frequently very rich ; the pay shoots are extensive and ftlrly regalar. The jtcrcentage of sulphurets, consisting chiefly of pyiite and galena, is small, and the gold is of unusually high value.

The red soil is <leep all over this hill and the outcrops are, as a rule, only traceable by means of the old pits and shafts. On account of the flat dip of tlie veins verticil shafts have here been extensively used for exploitation.

THB BMIIBT Mm niBB AlOEBtCAll VBIMS.

The oroppings of these extend in curved lines a short distance sonth

of the Hudson liay shaft . The Emmet dips south at 45 and the Irish American to the iiorthea.t at .'5.'). The Granfjer shaft, snnk to a depth 200 feet intersects the Emmet iu the bottom, having penetrated the Irish Amecleaa above.

Gbabs Yalubt Di8Tbigt.

THB mw TORE HIIX TKDr.

This vein extends with irregnlar cratcrape aontheast from tiMGhevanne

Hliaft. passiiijf south of tlio New York ITill shaft, where the Burfaco cropping8 are strung, aud tUeuce, largely due to the steep slope of the hill, parades an easterly direction and is believed to extend down to Wolf Creek. The strike is ou the whole west-north westerly, aud the vein belonjrs without iiiurh to the North Star system of oast-west veius. The vein bu beeu worked from the Clievaiiue shaft 350 feet deep on the inidine, at ebown by PI. XXII, bat tiie prindpal work has been ihnw im the New York Ilill {jrotind. Located very early, the Kew York Uill is estimated tu have produced $jO0,UUU between 1852 and 188Sb In 1866 and 1867 tbe mine prodneed $106,490 2,189 tons, yielding #49 per ton. Themine was then closed fur several years, until 1S71, when it was opened by means of a tunnel from Wolf Creek. From September, 187i, to October, 1875, the mine produced tbe yield being at the rate of Ikom $S8 to $49 per ton. It is to be regretted no maps anavaihible illustrating the occurren<!e of these rich ore bodies. The mine was in sucoeseful operation up to 1883, at whtoh time ilie shaft was opened to a depth of 1,300 fSset on the inidine, and 13 levels turned, with drifts from to 1,000 feet long. The arornge of the ore in 1882 is given as $25 per ton. The mine shut down about 188.'i aud ha since remained idle.

The vein Is tnm 8 inches to 2 ftet wide encased in liard rock; the dip of the shaft is S.*?" NE. The percentage of varies from 2 to 3, aud the value between $80 and $100. Coarse specimen gold is of occaneiNe.

ram mw aooKT bak vanr.

The workings on tiiis interesting vein are AiUy shown on PL XXII,

tlie iiiine liaviii been in operation bftwciii I'SO and 1885. Tlie sections show the existeuoe of two Hat veius dipping north and south and meeting in a curved anticlinal. A better ilhistration of the contemporaneous chararti r of tlie two flseore systems could hanlly bo obtaiiHMl. Tlie New Itocky Bar produced large quantities of cxtrcTiicly course gold in 188U and 1882, much of it being sold for thu manufacture of Jewelry. ITo data are available as to the production. The very flat "toj) vein" shown in the section has been worked through numerous small perpendicular shafts, aud found iu places to be very productive in coarse gold.

Thk Boweky Vsix.

A shafY a few hundred feet deei) has been sunk on this vein, which is parallel to the North Star, and outcrops 000 feet north of it. The shaft is 900 ftet east-northeast of the Korth Star shaft. The vein is

credited with a production of in 18fi9 (Raymond's reiwrts), and about 18r6 300 tons were extracted, yielding $15 per ton. The vein averages 20 inches wide (Beanos Directory).

238 GOLD-QUABTZ VEIiNS OF NEVADA CITY AND GRA88 VALLEY.

not unniiiAir vbix.

Thia deposit, which exfeMidB a short dManoe aoatli of the North Star, is not iloveloi>(><l to any extent. It was opened in 18<)5 by a verticiil shaft 60 feet deep und a tunnel 400 feet lon; the vein, which ftTwagw 12 ioohes m widA, lias prddnoed soom bMotilkil qteeiinanB (BeMi'a Dtiatoiy).

TIIK LAMAKqCK VUN.

The Lamarque Ilea about 800 fleet south of the Vorth Star and dipa to the aoaih. The vein waa worked with profit for aoTeral years, bnt has been idle lately, until in the end of i wliea it waa opened again and yielded aoine ore avemrin' ]m- ton.'

TlllC NOHTIl BTAIt KIN.

Hiator. — The North Star vein, oue of the most celebrated of the Graaa Talley depositH, was discovered in 1851, and worked to some extent tip to 1S.">7, yielding $200,000, accordin<; to Bean's Directory. It was known in early days as the Helx otia and Lafayette, and Hlake describeH it under this name iu ISoi. lu 1860 tlie uume was changed to North Staf, and tt waa eztenstTely worked np to 1S74, when it waa shut down and believed to be worked out. During thi.H ])ei iod it produced a hirge umouut, frequently hoisting 000 tons month. In 1860 it yielded at the rate of 124,000 per month; in IMO it produoad t330,(>IM; in 1870, iu 1873,9100,000; and the total pcodnot, 18G0 to ]S74, is irobably not loss than After ten years of quiescence the niiue was reoiKJued, in 1884, and it ha beeu worked oonttnnonaly atnca. In tiie oontinnation of the ahoot richer ore waa met with tliaii in the upper levels, and the production for the last years has been as follows: $413,200; 1800, $196,300; 1891, $266,000; 1802, 1893, $3.'t5,700. The production for the last ten yejun amounts to between $2,000,000 and The total itrodncttOD of the vein is thus not less than *."i,(>on.O<)0. In ISOI, owiuj; to reasons exjtlaincd below, there was a great decrease iu the productiuu, and the nine haa in the laat year worked ohlefly remaining ore hodiee in the levels.

JbteelopmenUt. — The shaft, following the vein on the incline, has attained a length of 2,400 fiaet, with a vertioal depth of 840 fteL Tlia extent nt tlie levels, as well aa the direction of the ahaft, ia shown on PI. XX I II. There is a 40 stain mill on the pro]>erty.

Country rock. — The vein is inclosed in u dark-greeu, hne-graiued rock of often chloritic aspect. It is in plaoea porphyritio by the development of small feldspar crystals, and ranges in coinpositiou from a uralite-diabase to a nralite porphyrite, the ante being rarely proserved. Otaina of pyrite, iiyrrhutite, and pyrita oeottr in the lock. Only toward the west is there any indication of change in

uxDOHM.] 0BA9S VALLEY DI&TBICT. 239

fbo couiiti y mck, as more fully explained The ontcrops of the ▼eiu oaa traced meaus of tUe uuuerouii litUo sbafte ou the hill to the eMt tbe far distmee of one-fonrtli lit mfle. In tbe oasteru part of the ontcropa hero are iiidicatioiig o£ a vein, which is to join tlif main vein tvt a depth of a few hundred feet.

As own by the levebi, the general strike of the vein is from westiiordiiraat to MrtbwBt but with mmay local imgularitittk Tbe dip Rhown by the on the plate, nnd will avemc*' 20', varyiiif; from lo° to 40°. The tructuce of the vetu is well iliatitrated by tlie excellent photograitbs taken hj Mr. B. A. Abadie, miperintendent of the XIII and XIV). The vein usually shows well defined, smooth hanging; and foot walls, to 4 apart. The spaoe between these walls is rarely if ever completely tilled with quartz; a large part of it ia oceapiad byarnalMd nnd altered oouftry sadi, and a qaarts vein magr lie at the wall (as in PI. XIII), in the foot wall, or. in fact, at any place between the walls. The width of the quartz does not average mere than 1 tooL In fdaoaa, aa innatnvted bf F1* XIV, the apnea between the walls may be |iractically oecupied by a breccia of quartz and alU'red country rock. In many places within the shoot the walls close down to a mere tMMim, as for instance, oa the 2,000-foot level. OnlBlda of liia wnlli tiia diabaaa la but IHtla altarad by Taia soltttfon, and is often fish mul hard up to the vein. The crashed rork wifliiti the walls is greatly altered, as a rule being impreguatad with pyrite and to a reat astantraidaead byoarbonafees andaerieitoy aa shown by analjrsis and description on pages 140, 152. The rock below the (juarf / vein in I'l. XIII is entirely similar to the specimen and the great number of veinlots shown by the )photo'raph in the rock are all fined witfei earbonates, tiioafh no carbonate is contain in the main TBIb. a striation. liorizontal or dipjiinfr slijihtly wp.st, is noUeed on tbe walls, lauded structure of the quarts by arraugeoient of tbe sttlphnreta,' aa weH aa a abeetinf dne to aabaaqnent dialacation, is quite omnnon. Fre(|neiit!y, however, the quartz is massive and the sulphurets are irrearly distributed. Oomb atmotore is apparently

The ore. — The pay is almost exclusively oootained in the massive quartz with sulphurets. The altTed country rotk betwM*n the walls contains up to a few dollars' worth of gold and is occasionally milled. The eonoeatrated pyrito In the altered eoontry rode oeotaina only in gold. The quartz in the pay aboot, nearly all good nn>, coiitaius $15 to $50 per ton, with but v:y little silver. Coarse gold in leafs or in bands through tiie quarts paraOd to the watts oeeora in placea. The gold is unnsnally flue, reaching S50. The average yidd ]irevions to 1>>7.") was $20, a!id 188-1 and isui the (|uart seemS to have hud a liigher average grade. The quartz from the cropping waa Twy rich, and Profeasor Blake reooxda in 1853 that mtioh coane gold oecnnred, and that 190 tone of quarts milled $9S per ton. Tbe

240 GOLD-CjUARTZ VEINS OP NEVADA CITY AND GRASS VALLEY.

quartz t-ontaiiia cent of sulpbureta, consisting cliieHy of rite with a little galena and liardly anything else. ( For analysis, see p. 128.) The ooneeutratod salphnrats ran from $60 op to tl90 and contain .silvtr in the ratio of 0.10 ounce 1 ounce gold. Thft vallMOf the concentrates varies with the ricbaess of the ore.

Ore hooU — The extent of the ore shoot is well shown on PI. XXIII, and it will noticed tiuife it dips to thu west oa the plane of the veitu Of course the whole area cxplori'd lias not been tHpially jiroductive, the richest portion probably being (hat below the twelfth level, and some levels are entirely vnpradnotiTe, bat oonalderad as a whole ttie oie sboot is indicated by tli workings.

Fault/i. — According to Mr. Abadie, a cross seam, striking northeast and dipping stop toward the sontheast, fiinlts the vein the seventeenth level; above this the faulting is said not to be notice* able. fault continues, though with smaller throw, on the lower levels; on the twenty-hrst level it is very distinct, and the throw amounts to 16 to 18 fiset along the hade of the flmlt. The cross seam,

which does not carry any (in:utz, would iutersiH't the shaft a little below the twenty-fourth level. To the west of the shaft the pay shoot has been Ibnnd to end abruptly alonp a vertieal plane laid almost due north tlinnigh the collar of the Ahaft, and it has been that tiieyeia has been cut off by a fault, usually referred to as a crossing. There appears to be some difficulty about the proper interpretation of the facts at this place. In the eighteenth level there are, indeed, several planes, striking north and dipping about 50° W., which intersect the vein, and on the maiu one a horizontal striatiou apjiears. Before leadiing this plane the vein splits; immediately at the plane there is

no direct evidence, of any great fault. West of (he ''croasing'' tlic vein is replaced by a single seam without quartz this was followed some distance, and Unally cross eats started in hanging and foot walls. In the hanging more solid rock was met, but in the foot wall there was found a .series of seams all dipping north in the crushed and altered diabase. It appears very much jis if the vein along the line of the crossing had split up into a series of string aa4 seams.

On the surface a short distance west of the shaft the sedimentary rocks appear, the contact running north; these clay-slates and cherts had not, at the time of my visits to the mine, been enoonntered in the eighteenth level, fhnn wllich it follows that the contact must dip west parallel to the cross seam mentioned. Ti is very likely that the change in formation a short distance westward may, as .Mr. li. C. Hoover flanks,* hsTS caused the breaking op of the vebi. The vein may appear again to the west, though the sedimentary rocks are less favorable than the diabase for a well-defined fissure; or a continuation of the pay shoot may be found in depth, the latter altematiTe having more probability.

Utatag SdaatUe pNWb Marab. IM.

V. a. flwtMMM. Mmcv

mCHTCINTM AMMUM MMRT MIIT U PV lOOi

OBAM YALLBY DlffTRICT.

Tfllt CKSmiAI. MOmt BTAIL

Condderable piosptM tin' haa been donetnward the east to find the

OOntinaatioil of the North star wiu, nml two .shutts, indicated on the map, were sunk on tlie Central North Star claim. Tin* nppiT shalt, 2U0 I'eut deep, 8true at that depth a pretty large barreu veiu dipping north. The lower Bhaft is started at an angle of ft2o from the horizontal and in a direction N, W., followinfr <lo'n a crushed /.one with pyritic impregnatiou, but no <{nartz. At MK) feet a veiu was Btmek, dipping SSo NR, and strikuii; northwest The rock, a normal diabase, is hard and fresh clOBe to the Vein. This vein, which is up to 1 foot wide, shows in places pood prospects. It is of course ditticiilt to decide whether theae veins really are the coutinuatiuu of the North Star flssnre.

Beginning at the Omaha mine and extending down the west side of Wolf for over a luile is a series of parallel veins having many couiuion features. They all dip to the west at moderate angles; all of them are inclosed in granmliorite; and most, if not all of them, are distingiiislied by rather alxindant sulphurct.s and a percentage of sUver in the sulphuretj iu excess of the u.sual amount.

This vein is the most prominent in the system and is traceable for a distance of 4,500 feet, the most northerly outcrops apiiearing on the east aide of Wolf Creek a short distance north of the Omaha mineand the most southerly a short distance east of the Hm prism sliaft.

The Omaha and Lone Jack Hiinrg. — The Oniaha and l.one JjK-k mines, worked by the same company, have for many years been heavy producers. The Lone Jack, in IS.")."., had in 18G7 a shaft r>(H) feet deep on the incline and was reported to have produced $oUO,ouu. The chief work on these mines was begin about 1875, and in the last years the}' have been steady The total output is said to i-each and iu the mint reiwrts from IHSi* to 1H92 they are credited with from $105,000 to $118,000. The Omaha shaft has attained a depth 4rf 1,500 feet on the incline; the Lone Jack, located 700 feet farther south, feet; and they are connected by drifts on moat levels. There is a 2'Stamp mill on the

The vein, which on the snrfiMe has a regular strike, develops notable curves in the strike. The lip averages 33° W, The vein forms a narrow tis.sure iu hard graniHlioritc, occasionally shiK'ted iu the vicinity of the vein. To the north of the Omaha shaft all drifts soon run into diabase. On the tenth level the diabase contact lies 20 feet south of the shaft. Diabase also an]>ears at the shaft on the fourteenth level. Kear the contact small' i ilikcs of w liite or nay, compa<;t and flinty

Thb 0K4Ba 8T8Tbk.

Thk Om.Kha Vein.

242 OOLD-tiUAKTZ VEINS OF NKVADA CITY AND GRASS VALLEY.

((luarty, porphyry) are met with. The vein is said tu usually beooDie iKor when infused iu this rock. The tenth level extends 1,000 ftet nwtiivard, Mwie good ore oeeurring in it in Imnclies, trat fiirthi r in the vein is disturbed by crossings and shows signs of splitting up.

Tbe vein is nsiTow, probably averaging 1 foot, and lies between well-defined

1iiinKiC and foot walls without much inclosed altered t ouatiy rock. Outside of the shoots the vein K*'"i'''""y closes to a scitm, so that pnvetically all iiaartz 18 good ore. The grauodiorite next to the vein is imiirsgMted with pyrite, bat on the whole is nnnsnally fteA and hard. Talcite >ccurs to only a limited extent in the wall or in the vein. There is very little bunded or ribbon quartz, most of it being massive, with snlphnrets in irregular diatribotion. The ok is of liigh grade,

ranging turn $20 to with abundant fiee gold 825 to 845 fine sometimes eoarse, inclosed in ipiartK, galena, or pyritc; it contains I per cent of Bulphurets, chietly consisting of pyritc and galena, with very little blende or chidoopyrite. The assay value of the conoentrates varies gi'eatly, from $00 np fo $.15(). The of silver in the sulphuretH is great, being over 2 ounces of silver to 1 ounce of gold.

Some pay hns been found to the north of the Omaha shaft, but the principal pay shoot dips to the south, iH'inning at the upper i u l of the Omaha shaft and extending toward tiie bottom of the .Iaei. Very rich ore was extracted from this shoot in 1894 on the fourteenth level. Another pay shoot, also dipping south, has been found south of the Lone Jack. A St "crossing'* or barren fissure traverses tlie vein ahmg the principal pay shoot, with a steep dip to the south. It does not seein to afflfMst the tenor of tiie ore. On the twelfth level tbe vein is fiuilted

0Ra8B Vallbt District.

about I foot by this rnssing, ith a relative downtlirow of the south 8idf, and on the fnurtceiitli level the carious relation illustnitetl in iig. 32 obtains at the crossing, showing a differential uioveuiunt of the heeto oonsdtatinff the ironing. A Bimilr eroM seam, fhuMng and

drsijipint the vein, is found :it t!ie end of tlie tenfli level north.

The itumeicurd Uouiid mine lies to the south of the Lone Jack. Only superficial developments were made np to 1M7, tbe vein having been worked alon' the surface for 1*00 feet. The shaft at pnecnt on the property has Iweii sunk to a depth of .TiiO feet, the incasing rock boinf; very hard. Two levels are turned at 165 and feet from the surface, the drifts extendinip a mazimnm diatanoe of 350 ftet southward and "tTii) feet north wunl. four distinct shoots liavinfr been found. Tho vein is said to be large. The mine was worked in 188U-9i).'

The Sarterff mine has worked two paranel veins. The old shaft is sank on tha southern end of the Omaha vein to a depth of flOO ftet on

Tn. n LantitndlMt iIwwIdc Aah, OlMka mtah taMMtb larry.

the incline. "The vein, which was located in 1853, has been worked at intervals since that time, but not more than ten or twelve years of oon< tinnous work has been spent on the property. Over have been taken from the mine, some of the ore consisting of extremely rich specimens of coarse girdd.* The mine was in ISU:) and 1. Prodnotions ranging from $19,000 to 439,000 are credited to the mine in tho United States reports for TfiO. 1890, and 1801. -Three levels are turned, at 308, 008, and 000 leet, extending north a maximum distance of 300 fbet and sooth 400 fhet. A drain tnnnel ftom Wolf Creek, 1,200 feet lonjr. interseets the shaft 2.10 fe't from the collar."'

Tho vein dips 30 VV. and is inclosed in hard it averages somewhat over a foot in width. The ore is of high grade, probably averaging about per ton. The amount of sulphnrets is said to Ite small and their value 950 per ton. In the mint reports of 1880 and

Tkatk Am. Sift, state MtaMadogtrt.

244 QOLD-<UABTZ VEIK8 OF NKVADA CITY AND OKASS VAIjLBT.

1801 tilt' iiiinc is I'n'dited witli a considcrahh' amoiiiir of silver, the reltiou bciug for tbu tirst ymkr 1,035 ouucet> of gold aud 871 ounces of flyer.

The Hvtery Ootisolidated sluift is sunk to a iloptli of 500 feet on the incline, on a parallel vein n -sliort distance east of tlie Oiualia vuiu,bat com|>ai-a lively little developuicnt work beeu duuu from it. The inc—ing granodknite is reported to be very hard.

TUB wuoomni-iLuiioiB van.

TluB is paranel to the Omaha vefn, and rope a few hundred fhet to

the west. It \raa worked at it.n northern end ftmn 1804 to and again from to 1870, during which time it produced a considerable amount of high-grade ore. lu 18C9 the old shaft was sunk to a depth of 500 feet ou the iiicliue, and the exteut of the stopes is shown on flg. 33, copied from Baymond's report for 1800-70, page 47.

Scale!

lu 1890 a new shaft was sunk on the vein 000 feet Houth of the old one: in 181U a depth nf feet on the incline was attained, with levels turned at ll'u and 2.lo fet, extending from 2UU to .'iUO feet north and south. The Toin dips W. 3So, is indosed in hast grsnodiorite, sometimes sliowiiif: sheetiii},' next to the vein. Tlie witlth averar.'es 1 tout aud the ore is of high grade, siveniging over $;JU [wr ton. Tiie snliliufet8,of whi 4perclt are present, average $00 per ton, chill.v in gold, and consist of pjrrito, with a little galena. The gold is 8.54 fine. In the old shaft there was nn extensive pay shoot sujuiosed to dip to the soutli, and tlu! jireseut shaft is sunk to intercept that in depth. There are also two smaller pay shoots of high grade, one on each side of the new haft A crow seam cnts the new shaft without diatnibing the vein perceptibly.

THK HtmnCMlTA VBIM.

The MinneeotaTdn, npon whidi the Sarprise shaft was sunk long ago may represmt the southern oontlnuation of the Wisconsin Teio.

Q&amp;Am Valley Distbict.

Tiif. Imkksix-Mahy Axx Vkix.

This vein, locutetl :,(>00 It-c-t west of the Allium liuiic-h vein, dips west from 30° to 450. At its soathern end the Phoenix shaft has been sank

on it, from which in 1870 some ore j iehliiiji $20 per ton was extracted. The developments iu the uortbei'u eud of the vein are flight.

THX AUMOS KANCM VBUt.

The oro|>ping8 of this vein, hKatciI about 3 niiles southof Grass Yal' ley, on the west bank of Wolf an; quiti' in<'onspi-nons and rnn

not be traced either Houth ur nurth uf the shaft. The vein wa.H accidentally discovered in 1854 by sinidng on the eroppingt. From that time up to ISTif) tlio mine was worked ontiunously, protbiciiij: IC.OOrt iuus of ore. >'iehlin;,' $2,400,000. In 1803 the mine became poor, bat the lUIowing year ru h qnartz was again (band. The product the three years ending DecemJwr 30, 1865, was $1 '.000. und were produced in 1H(>(5; the o]>eraHons wore snspeiidetl in Se])f ember, l.%0, and the mine lias remained idle ever Muce. The shaft in sunk ou the vein to a depth of 500 ftet on tlie incline, the lowest level eztendini 220 feet north and 211 fei t sdutli. A portion of tliijinii t/. on this Icvrl was very rich, but the greater part wan barren. There seemti to have been no adequate reason for abandoning the mine without farther exploration. The vein strikes N. fio to 1.".' W., and dips 40 to -15 W. Pliillips es t!ie width as 2A feet, while Bean's Diieetory states it to have been from 14 to IS inches iu the lowest level, where the vein was in part considerably broken np. There is a clay parting on the hanging urall. while the foot wall is without any distinet clayey division team the (puirtz. Phillips states that tin* average yield ou the lowest level was as as that from the njtper start of the tnine. Near the surface the deeonipo.sed ore was extremely rii li; Mr. Melville Attwood milled 21 tons in 1855 which yiehbd ><,I70 per ton.' The average of the ore from the deepest levels was also high. The quartz was iu places eztmnety rich; between these tranches some qnarts was fimnd that wonld hardly pay expense.s. There was a oonsideralde percentage of Bulpburets, chietly pyrite, but also galena and chalcopyrite; rich silver minerals were found iu a specimen from the Allison Banoh vein (see p.ll9).

While the Allison Ranch can not be traced far on the surface, there appears uu the hill to the south several veins striking north-south and opened by small proepeiA holes. There is in plaoee oonaiderable aheeting (if tlie granodiorite, the sheets dipping west. Large ouUrops show on top of the hill south-southwest of the Allison Kaiich, and ou the steep .slope eastward are several small veins, showing some qoarti with mnch pyrite.

Eiglitl) Ann. Rrpt. SUto Mlnnilog1*. p. 777.

NolM chiefly fna Omb'* IMnotoiy, J. A. VhUUf'a Hiaiiig sad MeUllurxjr of OoU swi Silver, tmi San Bwwm' Npwt tarllN.

246 GOLU-(jL'AKTZ VEINS OP NKVAUA CITY AND URASS VALLEY.

Almost duo north of thv Allisciii I'aiirh shaft, a distance of l,r>(M fot, ia tbu i' l'aukliu vuiu, uit wLicU iu early days cuusideruble work wan doue Mid a large mill once erected.

The Alli.suii llaiicli Ford-IIorscslioc vein is hx-afed on the wegt bank of Wolf Creek aad probably ia a ouutiiiautiuu of the Fraukliu or an adjoining parallel vela. The Hofaeaiioe aliaft it 3,600 feet nortli of the Allison Hanch and 240 feet deep on the ioeliae. The vein is tcom 10 to 20 inches thick.

THX POBBST SPSmO QWOVT OP KINBS.

Four nnli s sonth of (Irass Valley and miles with of Allison Ranch there is, on the east side of Wolf Creek, a series of veins of some importanoe.' The ores are similar to those of Oshorue Hill.

The Norambaiaa was worketl extensively between 1855 and 18i7. Its total piodtictioii is said to amount to $1,000,000 (Beau's Directory).

In pHMlnetion was JO.O'IO. Tlic mine was reopened for a short time in i sui' and is credited with a production of $2,500 lu that year. DnrinK the principal period of exploitation the' cost of mining and milling was $30 per ton. This very hi;;h figure is -videntIy due to the narrow character of" tlie vein. 'I*lie incline i.s ,"jGT feet long down to the litth level, atlainini; a vertical depth of 120 feet at that level. The levelB extend 1,000 lieet south and fiOO feet north from the shaft, and a ilrain tnnnel joins the shaft 4!K) feet from the eroppinps. The Norambagua has a northerly strike and a dip of 15 E., thus belonging to another system than the Omaha. It m contained in a bloeky granodiorite and is very narrow, rarely over 10 inches wide and more frequently 4 or 5. The ore is a bluish quart/, seamcil and Iniiiilcil witli ]>v' ite and arseuopyrite arranged in parallel ones, prtMluciug a rdibon like strut tare. The gold is rarely visible to the naked eye. The tenor of the ore is teom $40 to $100 per ton, and frequently about per ton (Phillips).

Sm QMiiMito AdM ar tk* Vail SlatM. Mi* y. IB, 8aMlmlUi CiL

Grass Valley District.

TIhto arc 1..'5.'5 jmt cent of sul])linn'fs. aci onliiifr IMiillips. Hcan's Directory gives 3 jier cent. These uru rather luw grade, being suid to

The Bourbon ins lie .'101) feet west of the NonimlMgii% and the Shiuurock 1,2U0 feet southeast of it.

THs ruacf OB L&n ueoo* vinr.

For many years this vein has been worked intermittently has been a eonHiderablo prmlurer. In the it is creilited with *.'mXM) in 1809, $5,000 in 18iM), and $13,100 in 1891. It was actively worked in 1BB3 and 189-1. The vein is opened by an incline shaft started in the tnnnelfrom Wolf ('reok. tM(>ffit fnnii its iiioutli, tlu* total length of the tnnnel being 1,8U0 feet. The incline is .sunk 'MK) leetoa the vein, which Strikes east and west and dip 30° S. The country rock is chiefly diabase with some cbiy-Alate,bnt theyeiu the graiiodiorite contact IjOtMi feet from the mouth of the tunnel. The ore ranges from #15 to $'20 ix-r toil, the gohl rarely Ixiing coarse and averaging 74o fine. Tiie aalphnrets, of which there are 3 cent, consist eliieflyof arseiiopyrite and contain about .'1.2.'> ounces of gold to 2 ounces of silver per ton. On the tunnel level the pay slioot is continuous for 1,000 feet, and large qoanUtles of ore have been stoped above It. Below fhe tunnel level the shoot appears to split into several branches inoUnin tOtboWMti contrary to the usual rale for veins dipping south.

-VBnr BYSTBKS OF PK.W.kvlvama, w. v. o. akd vhs wbbtbbm

POOT OF OSBOBNE BlLlt.

OKNKRAL FKATl ItKS.

The hills to the southeast of Grass Valley, usually referred to as the Kate Uayes and Ophir hills, are in an nunsual degree shattered by jointing or sheeting, and numerous qnartc veins are found parallel these systeuis of dishtcatioii. The proniiiwiit vein .system dips west at moderate angles, but there is also ample evidence of the existence of another system dipping east at about the same inclina* tion, and there is excellent evidence of the contemporaneottS formation of the two systems. The veins dipping east are best repre.<euted in the continuation of the system to the aouth-sontheast near the sonthem limit of the sheet. The deposits lie chiefly in grauodiorite, near the contact, while some of thorn are contained in the ilialjase. The gold is geucruliy of high value, often coarse; the sulphurets are taoderate in qnantt; arsenopyrite is not generally present.

Kxceptioiial veins are the iieirly Ciolden Treaswcii striking north-northeast, and the Little IMamoud, which dips 8.

Located on the sammitof Kate iiayes Uill, 4,000 feet south of the Grass Valley poatyttoe, tills vein was worked considerably thirty years

248 OOLO-42UABTZ VBIMS OP NEVADA CITT AND OBAjBS VALLEY.

ago, as is indicated by the pit along the cropiiingit. The total pnxlaotion is 8aid to have been $125,0U0, uiul the ore contaiiied from $35 to $50 per ton.' On tin* snmniit of llic liill is ji shalt .ioo fVi-t deep on the inclhie, on which work was rcsuuietl in 16J'> under the naiuo of Heda mine. The vein dipe 45 W. and is inclosed in Iiard irranodiorite.

Tbb Cbbhckmt Vbut.

The Creecent vein is located 000 feet east of the Kate Day ets and dipe to the east.

A few hundred feet fartlier wet the i'euusylvaitia vein is met with. The vein has been exploited at varloos times and jtrodnced a large total amount. of development has going on for the last five years, and in ISOi-O.") a considerable amount wa.s produced.

The vein, which i.s iuchised in gruuodiorite, can be on the sur-

VlO. 39.— Vprtlnal Kprtion ninns Itaft. alitiw ini: \-i uml flKKiin In the mlue.

fiicefor fei-t north of tkie shall, while to the south tin' -oiitinuity of the surface crop))ing8 is donbtfbl. The shaft is sunk to a ilipt h of 600 feetou the incline, the vein dijiiing west at an averafje aiifjle of A jiartof tlii shaft, c ontinued down at a stei'per antrle. struck a Jel vein belii-ved to be the Telegrapli, though this would necessitnte a a very flat dip for the latter. The vein averaires a little less than 1 font ill widtli ; the ntc enrrios frequently rnarsr pold and a small ]>ercentiige of pyrite uud galena. The wall ruck is generally fresh, or at least not extensively altered. The sheeting and fknetoring are very extensive and n-nder the VOrk of oxploitatum very dtflleult; the voin frequently itin<'lu's to a mere scam, dilVu nli to follow. Tlit> systom of flasnres dipping east is very prominent j at feet on the incline the Creseent vieln intersects the PennsylTania, and throughout the mine tlii if is a con.stant tendency of the main vein to throw oat striiij,'er8 dipping These relations are illustrated in lig. 35. Besides, there

Konwlk Cguaty Mioiag Uevtow.

Grass Valley Distkict.

18 a systi'iii '(iossiiit;s" or barron scams strikiiifr iiortlH'ast. tisiially

dipping at sU'cp angles. Must of these crossings appear

8onth of the fft, and at leoHt one of them throws the vein on the

fourth level 90 feet (measnred ulnn;.- the drift) in tbe foot wall — that is,

prfxliHM's a Moriiial fault with a leliitivi' dowiithritw of the south side.

The crossings euutaiu no quart/, aiul atlurd excellent conduits ibr the

rabtemuieMi cinsatation of water.

The largest ore bodies were found north nf the shaft the first

and third levels. The ore liody then to be ent off, hut the

apex of a new shoot was found on the fourth level south of tbe shall.

On the whole, the ore shoot thus dips to the south on the plane of the

vein.

rtm w. T. n. Tanr.

Only in the last fisw years has this vein entered the ranlcs of the large

producers. Loii<; known on the surface as a small to (i inch vein, i€ rajiidiy developed depth was attained. Tlie ion for the four yeans from I.s'JO lo 1.SU3 wa.s, >!.">3,000, #106,700, and 1143,300. The shaft is at present 1,400 iiwt deep on the incline, drifts extending a maximum distance of 700 ftet sooth and 000 feet north. '

The vein, which dips 32° W., can he traced in the granodiorite up to the Tele'frnph mine, where a small sliaft feet deep on the incline was sunk on it in ISOL'. Smith of the W. V. (). I), it enters tin' diabase and turns more soutliea-sterly, the vein at the same time altjuuing a steeper dip. In Little Wolf Oreek are not satisikctory. the vein cropping on the r'uluc to the south of it and opened by a tunnel 7U0 feet long, indicated on the map on the south side of the ridge feet south of W. Y. O. D. mine, may be the continuation of this vein. In the tunnel this vein is nearly |)erpeudicnlar and 2 feet wide. Tin' relation of the fjranodiorite ronf ict mi the siir- Dace and on the plane of the vein is shown in tig. 30, accentuating the wholly irregular snriteoe separating the two formations. On the eleventh level the I ontact was OKMsed, and partsof the mine are now in granoilitu ite. The contact is generally shari>; places liglit-colored granite-iKirphyry (quartz porphyry) is met with near the contact.

The vein is generally narrow, occasionally reaching 2 feet in width, ami sotnetiines cl tsing down to a scam. .V little calcite souietiines occurs clo.se to the vein in the country rock, which is much fractured ami imprefniated with pyrite Cavities filled with quarts crystals are coninnin on the veln. Theore consists of (juartz with finely distributed gold, SiHj to 8.12 fine. The sulphurets, of which there are - per cent, consist of pyrite, galena, and blende, with a little arseuopyrite in places. The sulphurets contain from 2.5 to 4.5 ounces of gold and ff to 8 ounces of silver ton, the richest being the galena fnim the fine slimes. The sulphurets from the altered country rock adjoining the Tsiu contain only from ftf to f 13 per Urn. The general tenor of theore

250 Ooi.D-Quartz Veinr Of Nevada City And Grass Valley.

is bigb, raogiugfrom $20 to $50 per ton. The ore sboot, wliicli was ttarroir in the upper part of tbe mine, widened between the sixtli and ninth levels, attaiuin a maximum length of 850 fleet; hdow tliis it showed a lower crradeof ore fnr some distance, and then iiiipoived again greatly. The slioot, though very irregular in it detailH, dips uu the whole to the oath on tbe plane of the vein. Thne far tbe largest ore bodies have been found in the diabase. Then arc a ininiber of seams dipping east, as in tbe Pennsylvania, and there is a tendency of the vein to fall back in tbe fbot wall on these seams. A great number of **onw8ings,' or barren seams, follow the ore Blioot down, with a general southwesterly strike ami stee] or vertical dip; thqr do not appear to throw the vein to any noticeable e.Ktent.

Scar*

Fw. W — HfttoBtol pfictlao cwtfattU cm atfaee ot> lAtMt et th t1ii, W. T. O, 1).miM>.

OTHSS vsiim.

Gloeely parallel to the W. Y. O. D., In strike and dip, are the Parr, Gassidy, and veins, on which only a small amount of development work has Im imi done.

Tbe (fohlen Treasure haft was sunk IfK) feet iwrpcndicuhirly to cut the W. Y. O. D., which, however, it failed to do, the vein here having assumed a steep dip. A cross vein 2 feet wide, and nearly perpendicular, outcrops just west of the shaft.

IMF lU I.I ION, ANO ALASKA VKINS.

Following the western foot of Osborne UUl, there are a number of veins with an easterly dip of about 45. It la very likely that tbey may in reality be one oontinnous vein with a general north-northwest

Grass Vallky District.

strike, but tlic outcrops can not be continuously fnlldwcd. The Big DiamoQtl vein outci-opH lor a few liuudred feet thot due east of the Omaha mine. It has been opened by a tunnel and small ebafl, nnd iu former years (1869 to 1872) a considerable auiount of ore, avcratnj; $i.'0 or more per ton, has been extracted from it. The vein is 8aid to be feet wide.

The Little Diamond is a erode vein dipping 48P 8. and ooataining a sliiMit of ore dipping to tlie west on tiniiliino of th<- voin. It is opened by a shait 290 feet deep oa the incline, but uu work has beeu done on it in recent years.

The Galena and Bullion vein wa worked at its northern end, known as the lone or Cialena, in 1865, hy a vertical shaft 140 feet deep. The vein is 1 to 4 feet thick, the ore averaging $2U (Beau's Direi;tory). The gold is 815 fine. On the southern part the Bullion shaft (formerly known as the I'nion .Tjick'') has been sunk to feet iMTiicndicnlarly, with drifts aggregating 500 or 600 feet. The production is reported to be $500,000, tbe width 1 to 4 ftet, and the ore to contain $8 to $60 per ton. It has been idle for a long time.'

South of tlie Bullion lies the Alaska shaft, sunk lUO feet perpendicularly, then for 400 feet following the vein. South of the Alaska the vein bends to the southeast and enters the diabase area. The Leber, or Presqu'isle, l,.5O0 feet south of tlie Aliiska, lu'loiigs tO the Same system, and has yielded some jiowl ore I'loni a Moot vein.

The Franklin is located east of the Alaska, higher up on the hill; it has been worked intermittently by means of tunnels and a small incline, and yielded a considerable aggregate sum. The vein lies chiefly in decomposed diabase. Imt its nortliern end cuts into the grantsliorite. The dip is 33" W. The ore is of -high grade and is rich iu sulphurets, the gold being 808 fine.

In the lower part of the niviue into Wolf Creek due esvst of the Wisconsin mine, called Little Diamond Itavine, two veins are found — the Snowpoint, opened by a tunnel feet long, and the Portland, a strong vein outcropping on tbe side hill east of the ravine. The riirtland is said to !u> 4 feet thick and rich in salphurets, and has proilucetl some ore ot medium grade.

This complex of veins, exteudiuf; for nearly miles with a general direction of 2f. 17 W., forms an excellent example of a "Gangzug," or qrstem of linked veins." The veins lie throughout in diabase, diabnseporphyrite, or poridiyrite-breceia. Tlie dip is always to the west, avenigiug 35. iu spite of this general similarity the ores are not identical thronghouL Frmn the Orleans mine southward the eastern

TIIK KKANKLIN AXI> ilTIIKit VEINS.

The Bmimrk O8B0Rnk Hill Vein System.

Vanta Cmniy Hininc BoTiew.

252 Oold-Quartz Vetn8 Op Nevada City And Grass Vai-I.Ky.

part of the system contaius a lower grade of gold and is particularly diatinguisbcil -by a eoDsiderable percentage of arsenopyrite. There are two main branches — tlio Wu h Hill and the Ophir Hill, the latter being the nmro exti'iisivc. iSotli join at tlie Maut'iita mino. ami beyond this point appear tu break up into stringers. The Mageuta shaft is annk on the vein just north of the Jnnotlon to a depth of a few hundred feet on the incline. Tho mine was worked a small scale at (liflVrciit times up to about ten years ago. " Between the hei ond and third levels a vein known as the Mohawk interseeta it right angles." '

The Kmpikk Mink.

The Etupiie enjoys the distinction of having been worked more netirly eontinnoiidy than any other mine in the diatrict, having been in operatioii

wifh but short from its discovery in IfCH) to the present time, iietweeu lSo2 and it is reported to have produced $1,00U,U00, and from 1864 to the close of 1866 the oatpnt was tdOO,000. In 1866 it KL'IK) tons per month. In 1800 the output was A.">ll,(KMt; in 1870, $'_MO,<MMt; in ls7;i, in 1874. 9il.S7,()(>(; in 187."., )?23l',O()0; in 1803, tlKSSOO. le total prodaetion is probably in the vidnity of

The Empire haa a shaft J,10U feet deep on the incline on the Ophir Hill vein, as well as a smaller shaft on the Rich Hill vein. The drifts

on the main vein extend to a maximum length north l,.5O0 feet and south 700 feet. A 10. stamp mill reduces the ore. The vein t arries a large amount of water, the cross seiims carrying it down from the whole hill. The ontcroppings of the vein lie entirely in a fine-grained diabase, but at iir near the elcvciifh level vein cuts across the contact into the These upper workings are not iiccessible now. Smaller dikes of granodiorite were noted on the fifth and seventh levels.

Tlie vein has a northerly strike. cliMiifjiti}! in (he Kouthern of the mine to north-northwest, with many curves and local irregularities, the dip, which is MtIj regular, averaging 24P W. The vein is narrow, nsnally from 10 to 18 in<'he< wide, in structure is very similar to the >'orth Star vein. There are usually two distinct walls, 3 to 4 feet apart, with quartz vein in the lumging or foot, or Itoth, and seams also traversing the altered oiintry rock separating the walls. (Si-e PI. XV.) Outside of the (issnred zone (he diabase is fresh and liard, while within it is usually e.\tusively altered by curbouati/ition aud traversed by seams of calcite. Occasionally smidl open flssores are found in it coated with calt ite crystals. It is also usnallj' iinprernated with and this replaced country rock, when Ibuud near rich quartz, may contain two or three dollars in gold ton. Gold has been observed to oecnr occasionally inclosed in the deoompoeed ooantry rook. The ore

coii-i-ts of qiiartz with ofJt-n coarse. fnH field 805 fliio. Tlic quartz is partly partly loaive, and ooutaiiis3 jier cent of sulphurebi, chiefly pyrite, with little galena and occasionally blende and ohalconrrite. Arseiiopyrite is The concentrated sulphurete contain from 3.." nj) to ounces of ifolil and about 2 onncos of silver. Large parUsuf the shoot have averaged 930 to per ton. The main pay boot extends on both sides of the shaft and is somewhat ineftnlar in s1ia]>i'. lion<?li it is stattHl that the richest ores arc from shoots south on the plane of the vein. The great'CSt length of Htoped ground is 2,000 feet. On the thirteenth level the van is split into three pa i the division extending,' several hundred feet north and MOth. Tiiis break. fM-cnrring in the inaiii shoot, made the cvjiloitation very lif1cult and diminished the tenor of gukl in the veiuH. l;.\cellent ore 18 inches wide waa, however, atoped on the twentieth level north in 18M. The distance iH twecn the brandies makes it doabtftil whether tiiegrwill join again iu depth. Several strong cross seauiR run through the iiortliern part of the mine, and have been observed to

fault the vein a little. , ,,

The relations illus- QuartTMSmmLiJ trated in fig. 37 were shown in the stopes a little below the twentieth level.

The Bieh Hill vein, w.— iiMgHnaiim .H.-tion. nbowinK rauit. opWrBiiiTCto.4 dippingaOOM ., and

approaching the Ophir Uill iu deptli, han been opened to a less extent by an incline shaft and by means of a cro8.scut fVom the sixth level on the Ophir ilill sliaft. (iood ore was 8to|)ed from this vein in 1894 on the so-called Kii-h and Laton shoot, which is said to be feet lonjr. For some distance above the sixth level the vein is divided in two, joining again above the fifth level. The hanging vein is the better, showing about 12 inches of massive quartz with ]>yrite galena, and is inclosed in diabase, hard and fresh close up to the vein. This complete absence of emshed or altered wall rock is mmewhat nnnsnal. Brown opul containing coarse gold has been noted from this shoot.

Tlie I'icli Hill continues southward tlirtnigli New ()]tliir and Daisy iiill claims, on which the developmentji are not ext-usive. A shaft| 300 feet on the incline, was snnk on the latter many years ago, and the mitir is re|(orted to liiive been rcojyeiicd in 1895. A branch VCln iS Sftid to connect with the OpUiiliili vein at the Prescott shaft

254 Oold-Quabtz Tbins Of Nevada City Akd Qbab8 Valley.

THK OELKAXS lUHK.

TheOphirllill voiii doubtless (rontinnessOHtlnvuKi lowiinl the OrlejuiB miue, tliuugh tLo cioppiugs du nut how quite contiuuuiisly mi the arface. The old Orleans shaft was sunk to a parpsndienlar depth of 100

fci't ; the new sliaft. st;irtf'(! ;i fi-w years af;f>, inclines .I'lO W., the cruppiiigti lying 8omo distunco cast of the shaft. The dcptU is 325 feet with drifts at 200 and 280 feet A considerable amount of ore has been produced by the Orleans. The gold is 790 fine. There are 3 per cent of 8ulphuret, avcrapinp 3.5 onnces of gold and 0.7 otuiop of silver. The vein continues southward by I'rescott, Betney, and King Dill shafts, all worked to some extent many years ago. King Hill and I'rescntt shafts were sunk to a deptli of feet on the ineline. The long Orleans tunnel drained the surface workings as fur auutU as the Betaey mine. This nanow vein appears to have been charaeteriwd by a strong percentage of araenopyiite and rioh ore.

Lying with the Ophir Hill yein and several hundred feet east

of it is the Heuston. which can traced only l,5()fl feet on the siirfaee. The deep explorations un this vein begun in 18UI and were continued ' until aboat 1870, since when the mine has been idle. The shaft is 300 feet on the ineline, dipping 2.'P W., tind the .neverul levels extend north and Houth. The veiu is very narrow, averaging 8 inches, inclosed in hard diabase, but very rich. It yielded $500,000 between June, 18G4, and April) 1867. Some ore containing $IC0 per ton was mined in 1867. The expttiies were estimated to have been $45 per ton in 1867.'

At a distujieo of 600 to 700 feet east of the SOOth end of the Ophir Hill lies the iSebastopol, also dipping weat at SS. The :Se))asto])ol shaft was worked 180 ftet on the incline between 1856 and 18-~>s, yielding 200,000, and was a'ain opened fbr a short time in ISSO.

The southern end of the vein has recently been openetl by the Elctric shaft, sunk to a depth of 400 feet, dipping 30 W., and with drifts extending 150 feet north and south. South of the shaft the vein turns to the southwest. The ecuintry rock is a diabase-lireecia; the veiu is 1 to 2 feet while, and the ore Ciu-ries finely divided gold with pyrite and some arsenopyrite and galena. On this and adjoining veins the pay shoots trend rapidly to the south on the plane of the vein. Two smaller veins, whieli have been worked to extent and proved to well, lie between the King ilill and the Electric, the Sanders on the east and the Payday on the west

Okass Valley Distkict.

THE oenoims hill tux.

General featurea. — Hegiuuiug a short diKtuiicc west of King nfll sliiift, tlie Osbonio Hill voiu ran be traced lialf a mile south southeast to beyuiid the Centeuuial sUalY. Ou the east side of Usbornu Li ill there are no ontooppingB fbr 3,000 itot, when again a vein appears wliidi possibly may represent the extension of the Osborne TTill, having tlitt same directiou of strike aud dip aud the same cbaractedstiGa of ne. Very little wwic has been done on this aontherly extension.

The 0$bom Hill mine. — Tbe principal developineiits are found at the Oslmrne TTill mine. T-Vom IH/ili to the vein yieldeil lure returns from the hurlace ore, the slopes extending KM) to 180 feet ou the iucliue for SSOO feet sonth of the shaft and 800 itofe north. Between 1865 and 1>?T() the main shaft was sunk to feet and inaeh ore was extracted. The luiue was idle from 1870 to 1894, when it was opeueti agaiu, the shaft snnlc to 600 feet on the incline, the drifts extended, and a 20stamp mill erected.

The ehara<'ter of the wall rmrk varies somewhat; it is in part a very Hue grained urulite-diabase, in part a ii()rubleude-pur]>hyrite or a breccia of porphyrite and brownish argillite or sandstone.

The vein strikes north northwest with many local curves aud irregularities, aud the dip varies irom 29° in the upper levels to iu depth. In some parts, as on the fifth level north, the vein mns down to a seam, which, though containing rich ore, is too small to work. The main ore bmly was exposed on tlie tifth level north, whicii shows excellent ore to 4 feet wide and suui to average $30 to $40. The foot wail is well defined, the hanging lees so. The makes less the impression of a continuous open space with ipiartz than of a zone of crushed rock 1 to 3 feet wide, coutaiuiug many smaller open lissures and spaces subsequently filled with qnarts. Comb straotuTe and vngs filled witii crystals are very abundant. Banded stmotore by deposition and ribbon structure by subsequent sheeting oi-cnr. The country rock between aud ajoiuiug the walls is very much decomiiosed and converted into seridte, there being bat little earbonates. It is, besides, filled with in small crystals. In the ([uarfz free gold is rarely visible. The ore curtains arsenopyrite, with some pyrite and a little xincblende, galena, and oocaaionidly ohaloopyrite, in all per cent sniphnrets. The brown blende occasionally contAins coarser gokl. The gold is 767 fine; the salpburets contain very little silver.

In a few places there are indications of a system of joints dipping 30' 1".. Several crossings cut the vein without faulting it. and have an easterly strike aud a steep dip north or south. OccasiouaJly the cross seams carry some quarts, and in one instanee tetrshedrite was found on one of them.

A branch vein with steep dip, called the Shoody, lies to the west of the Osborne Hill mine.

866 ooLD-QUAirrz sims op mbvada city and grass vallbt;

The OemiennM mine. — South of the Osborne Hill mine probably the

Bute vein is workeil by the Centennial shafts. Tliis Tiiinr was worketl between ISTtlund 1883, producing a related tutal of 4UUU,000. lu 1803 work was resumed on the new shaft, bnt soon stopped again. There are two shatt.s; the ohl one is several hundred feet deep, and the extensive dumps iudieatw that a threat amount of worl; lias been it. The new shaft, 300 feet farther south, is HM leei deep on the incline. The vein dips W. 30°, and is contained chiefly in porphyrite-breccia with many brownish frajjments of tliiity rocks. The quartz, which averages 1 foot in width, contains likely divided gold and a considerable amount of sniphnrets, chiefly arsenopyrite, with mncll pyrite and a little galena. Galcite, in largo cleavage pie<'es, is frequently found in the altered country ro< k adjitininr the vein. The pay shout is sjiid to beloO feet long, rapully trending south on the plane <tf the One or two erosa seams ent the vein without foulting.

Thb Lavatbttk And Oukkt Yeox.

Extending diagvmally acnes Osborne Hill, with a strike a little west

of nortli, this strong vein can be traced for a distjincc of 1 J miles. Comparatively little work has been done ou it. At its northern end the Conlan shaft was snnk 190 fbet on the incline in 1802, disposing a vein of 20 inches and some ore. The vein dips W. and is ini'loscd in iKtrjihyritc lucrcia. Between the Conlan and the Lafayette tuuneLs the outcrops are not very distinct, but south of the latter mine they ean be traced easily. In the Oonlan thero are said to be two ore shoots pitch in; sonthwest.

The Lafayette tunnel strike the vein 4uO feet from the mouth, and drifts wre extras on the vein 80 ftrt north and MO feet south. The vein dips W.; the ore is ribboned qnartx with pyrite and galeaai and contains $i20 to ])er ton.'

The Comet tunnel, further south, cuts the letige 000 feet from the month, and a oonddrable amount of ore has been stoped at various times.

At the southern eud there are two strong veins on the Indiana claim; on the mre westerly of these a perpendicular shaft has been sunk 80 feet deep.

THK VBINS OP BOUGH AKD BSADT AUD DBADMAVS thAX.

In the vidni of Bough and fieady, milea west of Grass Yallcy, there are several smaller veins, usually rich in pyrite and other sulphides.

The Oaceola rein, inclosed in amphibolite, striking east-west and dipping 00° N., has been devebqied by two tunnels and a small shaft;. The

Trom liiil. in gabbro. miles west of Grass Valley, dips A't' W.. and is opened by a 200-foot inclined shaft. The ore is strongly sulphureted,

Steveotb Add. Urpt. SUkt Miiieralo||it.

Grass Valley District.

containiiitr uivjut 20 pr ton. The vein 18 said to be 2 feet vide and was worked to Home extent in 1881.' Flat is situated mitos to the vest-sontfaireet of Gnm

V.ill< , on tbe rolling; |ilat<';m extending in that direction. The surface gravels in tbe j'tiU hes of this vicinity were extremely rich in coarse gold, aud several promising quartz mines have been found there. The YeiaUf which are indicated on the Smartsvilie sheet,' lie in the mostly massive, rarely sehistose, ani])liih()lite area hefween two masses of gabbro. The grain of the rock, which is chietly of dark color, varies greatly, and in places unaltered diorite or gabbro is found. The whole area to be a partially dynamo metaniorpliosed diorite and gabby. The veins form three groups, with a generally northerly strike, and generally dii> west. On the north lie the South Star claims, followed southward by the Calilornia niine, alsoknownoAthe Pittsburg. This vein, wliieh (liis ti."), has been worked at intervals, aud at times has been a considerable producer. The shaft is 280 feet deep. The ore oontidns coarse gold, 0 to 10 per cent of sulphurets, and a total of from $40 to *7" per ton. Tlio vein is said to average 1 foot in width. It is credited with 250 tons of ore iu 1875, producing $20,000, and with 116,000 in 1891. The total production is not known.

The Sccen-thirty rein, one-half mile south of the Califoniia and dipping W., extends through two hx ations. It has been worked at various times by two incline shafts 200 feet deep. The vein is 18 to 24 inches wide, aud has produced a notable amount of one. The aorfhce ore lia.s for several hundred feet. The ore is white quartz with but little sulxthurets, aud is said to average $20 per tou iu the shoots. The superintendent states tail the flneness of the bullion exceeds UOO, which certainly is most nnUBOal. The mine is credited with $ll,2<)o in ISC)'.). In 1893, .300 tons were crushed, yielding

The Xoniianilic veins are located 1 mile cast of the Seven-thirty, strilie a little west of south, and dip 40° W. The shaft is 120 feet deep. The two veins, 40 feet apart, average G inches in width, but contain very high grade ore. A cross vein, called the West Hormaudie,

; , oinclo AtlM of tlM Uattud aubm, MltoKo. U, S—ifwmiib Ori.

Ohaptbb Xvii.

Introduction.

The milling districts of City iviid Orass Valley are situated in Nevada County, 135 miles northeast horn iSau Francisco, ou the weatem slope of the Sierra Kevada, at an elevation of about 2,500 flaeb

A great number of important gold dtposits. coiisistiiif of qnarts veins and gold-bearing gravels, are concentrated in this vicinity.

The districts were discovered in 1849 and the minea have been worked eontinuouMly since ttiat tirno. At ])re.4ent the qnartz-mining interests are by far tlio more itiijxntanl. The. districts ar' estimated to have produced a total of about 9ll3,(KH),UUU. During the la8t years the Grass Valley district Ins Mumally pimduaed an average of 1860,000 and tho Nevada <'ity district t400,00( all in gold; the silver prodnotion is oouiparatively iugoidoant.

Geology.

is made between the Tertiary and lieceut rocks, called the tupetjfawnt series, and the pre-Tertiary rocks, called the M-rodb series. The latter contains the quartz veins, tlie former the placer deposits resulting from the disintegration of the veins. The districts lieatflie border line between the fiiothills of igneons roeiks and the m-ddle slopes of sedimentary formations of Jurassic or older age. The rcM-ks prevailing in the vicinity are chiefly of igneous character. Only a lew ureas are of Ncdimeutary origin, and consist of siliceous argillite, slate, sandstones, and sohists of partly Jonissio, partly GarbonifBrans age. They are generally altered, but rarely so much that their origin can not be recognized. The igneous rocks consist of granodiorite, diorits gabbro, pyroxenite, diabase, and By metamorphic iiroce.sses nmphibolites Imve in pla(>es been formed from the diorite, gabhrtt. diabase, and while the in roxenitc and jieridotite often have been ciianged to The igneous rocks are of Jaratriaa or lter age, with the possible exception of the diorites, gabbros, ami peridot itcs. T'eginnfng with the latter, the eruptions were continued by the diabases and porphyrites and closed by the great intnisions of granodiorite of probably early Oretaoeons age. The period of maximum intensity of volcanic activity appears to be contempora* neons vith or a little later than the dose of the Jorassie. tf8

'1

The oldest sedimentary nraka wwe folded and oompreaaed before tlw

igiieons activity had commenced. After the close of the Jurassic a Becond folding and compression took place, which metamorphosed many of the igneoas rocks jast erupted. SnbMquently to the intrasioa of the granodiorite the metamorphoauiK inflnenoea bare been slight, bat the range was subjwted to great oomptpssivc stifsa. prodnoitig systems of joints and fissures on which the quartz vein were formed.

Indiaettssing the metamorphic prooeases, distinetion Is made between dynamo inetamorphism, dynamo-chemical nietainorphisin, coiiuuon hydro metamor]>hism, hydro-thennal metamorphism, contact metamorphism, and weathering, all of which are shown in this vicinity. The different waya in which pyrite and pyrrhotite may form are described; also tin* course of tho in th' feldspars, vvliicli cliiefly are converted to micaceous products, and possibly scapolite, but not extensively to kaolin.

Thb Fu8Urb 8Y8Tbm8.

The eompresslve stresses to which the range was subjected after the intmslonsof granodiorit<- jikmIikimI joint systems in different directions, trayersing all rooks of tlio 1k (1 rock series. Sometimes the joint plates ate thiu and a liheutiug of the rock is pixHluced; at other places the spacing was much laser and a series of parallel flasnres was prodneed. The fissure systems may be ilivided into north south veins dijtping either east or west at moderate angles, averaging 35° or and the several groups of east-west veins dipping either north or south at high or low aiijles. Kach direction of strike has its two directions of symmetrically opposite dip, which are referred to as conjugated systems. The faults on the veins are in general small, but on the Merritield and Ural veins great movement has taken place, resulting in a throw of probably over feet measured along the <Iip of the vein. Xearly all faults recognized are overthrnsts. The north-south veins are older than most of the east-west vdns and are foalted by them. It ts further shown that the fissures cross the contact.s without being influenced by them, except as the susceptibility to deformation and breaking of different rocks is concerned.

The origin of the fissure systems is shown to be MHnpressive atreasea, vll;1l will, as indicated by experiments, pradoca anch ooiyagated fractures a-s are observed here.

Products Of Vbin Formation.

The products of the vein-forming agencies are:

1. Quartz with native gold and metallic sulphides. This is formed by deiwsition in open spaces along the fissure and constitutes the ridheat and generally the only kind of ore; and

2. Country riKik, altereri by metasomatio ooesses. This aa a nilo contains very little, if any, gold.

260 OOLD-QUABTZ TEim OF NEVADA CITY AKD OBABS VALIAY.

The gold is genmdly iu a finely dividtnl stnte, tbongh in inauy mines ooarso gold also occurs. The fret' tx-rnrs in Hitnihir quantities at all deptbH and is generally atcsociiited witli Kulpbide. Tlic value of the free gold geDerally flur ezeeeds that of the gold Mid eilver in the OlpbideM, tlioufrh in a few initK's the latter may equal tlie former. The flnenesB of the gold bullion varies from 700 to 850, and averages about 800. Th Bolpharets, oonsleting of predcnniiiaiit pyrtte with galena) blade, eloopyrite, sometimes arsenopyrite, and small quantities of tellarides. generally inake from 2 to .S jkt 'iitof the ore, ranging fronj one balf to 7 per cent. Tlie value of the sulphuret varies from $W to #400 per toDf the quantity of silver by weight frequently exceeding that of tti<' Small <|iiaiitities of and ciulmiiim have been fntiml. The value of the ores ranges from 90 upward. The average value is probably between $15 and 020 per ton. The Qiass Valley Mid Banner Bill veins oirry somewhat richer ore than the UTevada Olty mines. I n Htruetnre tlie ore maybe: (1) MsisHivo, carrying massive quartz witli irregularly distributed sulphurets. (2) landed by de[>0!iitiou. Both these fitmna show transitions to oomb stmctnTe and dmay stroetnre. (8) Ribbon stnictiire by movement on the vein. This is explained and illustrated iu detail. The quartz under the shows all phenomena of emshing, and tiie salphurets are pressed out. The gold is often concentrated on the planes of sheeting by a conoen* tration to the movement. (4) Banded structore by reopen* iug or successive openings and flllings of a lissure.

The qnarts is shown to contain soluble sulphates and chlorides.

The rocks nvxf to the walN and frank iits inebuled in the quartz sbow extensive alteration to carbonates, sericite, and pyrite by metasomatio processes; the pyrite contains very little gold, and very rarely is there any free gold in the wall nxk. The chemistry of the itrocess is explaiuiMl: Silica and soda are removed; potassa, lime, and sulphur are introduced. All ordinary minerals in the rocks are attacked by vein solution. A silicificatiou of the wall rocks is not recognized.

Along certain veins there is also an extrusive meelianical alteration of the rock, consisting in the production of schistose structure and emshing of the individual minerals.

The simplest of structure is produced by filling of open siKices along a dnge Assure, the open spaces being caused by movement along the pkme of the Homewhat irregular break. Mere OMipUeateil structure may result where tliere are two or more (Issnres, nearly paralielf the space between which is largely with country rock, usually breooiated or crushed. Then the quarts will depoeit in the open spaces between the rock fragOients, forming more or less irregular and winding veins between the ]arallel fissures.

The width of the quarts along the fissure varies greatly, and places

Structure.

Summary.

where the vein pitches out to a mere seam occur abundantly in raost veins. The average width of the larger veins may be from 2 to 3 feet, while by far the liirgest number are very much narrower. Some of the most productive veins average but little over a foot in width.

No distinct relation between country rock and the contents of the veins can be rec4igMized. Veins o<!cur in practically all rocks of the district. The nictasoinatic processes are alnioHt identical in all rocks. The character of the tilling — the qnartz — varies greatly, but is not constant for the same rock. It even varies in different ]arts of the same vein in the same ro4-k. Some veins in granodiorite and argillite ar6 rich in silver and carry abundant sulphides.

The influence of is very prominent; generally veins from the same vicinity carry similar ores. On the whole, the great concentration of deposits ill and about the granodiorites of Nevada City and (irass Valley indicates that the veins are genetically connected with this large intrusion of acid magma.

Pay Shoots.

The riidi ore usually occurs in fairly well-defined bodies, or pay shoots. Tliey are, as a rule, long drawn bodies with their maximum extension in the general direction of the dip, but with an ordinarily well defined pitch on the plane of the vein. The rule in this vicinity is that the ore shoot di)>s to the left of an observer standing on the and looking down in the direction of the dip.

The pay shoots vary in length from a few feet — those generally being called pockets — up to several thousand feet. On each larger vein there are usually several pay It is very common for one shoot to cease in depth or be subject to local impoverishment, but thorough exploration will usually result in finding new shoots or a continuation of the old one. There is no gnulual impoverishment of the ore in depth, while frequent changes in value occur. The depth at which gold quartz is no longer has not been reached in our present explorations.

Genesis.

The veins were formed by arpieous dejwsition and by thermal waters containing carlxmates, silica, alkaline sulphides and sidphates, gold and metallic sulphides, the latter ]>robably in a stitte of solution. The heavy metals were probably leiu-hcd from the rocks traversed by the solutions at a great depth. It is shown that the heavy metals in the veins have probably not been derived from fhe immediately adjoining wall rock, though gold and heavy metals nuiy, and in fact do, occur in them.

The solubility of minerals at different temperatures and pressures is investigated, with the result that there is generally not an indefinite increase in suliihility by rising iciiipciatiiro and pressure, but a certain whii ii can not bo cxcecdcil. From this it appears probable

262 Gold-Quartz Veins Of Nevada City And Grass Valley.

that decrease of teinpi'rature and pressure iu waters approaching the surface Is not an entire!}' dominant factor in the formation of mineral deposits. Considerable split-a and sodinm salt have been oonstautly Riibtrarted from the wall rock diiriti' the vein-forming proccSB, and a part of the quartz in tlie vein 18 derived from this silicA. It is suggested that the deposition might be due to a distnrtmace of the eqnilibriaminthe concentrated solution by material constantly aided from the wall rock. The gold and the sulphides were probably largely' deposited mechanically with the silica. The country rock to have had no speoial pcedpitatiDg ioflaenoe on tb aolntiona.

The Superjacent Formation.

The auriferous gravels of Xeocene age are briedy described, and it is shown that they had not aconmnlated to any considerable depth at tha beginning of the volcanio period.

The bed nx'k surface upon which tliey is restored and shown by contour lines. This Neocene topography is discussed in detail, and ft is shown how ths inoongnioas features of the map in ngard to the grade of the streams are made harmonious by the supposition of a tilting of the Sierra Nevada along its eastern edge. The rocks of the Tolcanio period, inehidlng rhyolite and andesttle tnih, are briefly described, and it is shown that much of the heavy gravel bodies ot Nevada City was due to tlie diinimiiijr of the channel by the first rhyolitic (lows. The last andesitic mud tlows covered the whole country here described, Banner Hill and Osborne Hill akme pntfeeting above the level of the lava field.

Addendum.

Aocording to data Icindly ftamiehed by Mr. Oharlcs G. Yafo, statistician T'nited States Mint, San Francisco, the jtrodiiction of the Nevada City and Grass Valley mining districts in recent years, including all quarts and placer mines, to as fMlows:

Im.

IMi.

aT,43S.ss

Un.

NtradaCily, including Willow Viilirr . Ohmm Vallay, laeladlag Bangh aiul

Total

MS, moo

IMM,Me.M

i,B.as.n

l,2aa,8l3L47

Index.

AbenlMn, S. Dak artesian welli at .

Iso.

ua

lft.t71.07A

lulyila of artealui water from well at . 977 Adella Hia Silver CHIT. Colo.. dewripUon

and history of. 417

Alaaka vein. Graiw Valley, Cat., dMrriptian

of au

AlratT, 8. nak..arteaiali wellnmr 072

Alexandria. S. Dak., artesian wells at and

near MO, 071

Allison Ranch rrin, (irass Vallvr. Cal.. d- srriplioo of

Alliiriiim of Kevada City and Grasa Valley dintrlcU. California, description of . . .

Alliivliiin of SlWer Cliff and Rosita nilla,

Colorado, description of 333

Alpha vein, Orasa Valley district, Callforuia

. deacriptionof 221

Attaile uf quarti Tcina of Kerada City and Oraas Valley districto, California, ocoarrence of

Alumiuom hydrous sulpliate of Nevada City and Grass Valley districts. California, occurrence of

Alunlt4> pseudoniorphii, Kosita Hilts, Colorado, description and analysis of 318

AmpbilMllte KTonp nf mcks, Nevada City and Grass Valley districts, California, deerriplinn of 713,

Analyses, chemical 38,4i3,lS.ifi.lLM.

Si. 82, eg. ff7, em. 71, 75, TR. BI, 90. 121. 122, 123, m-lZ?. 131. 149 150. 151, IMi m, 155, ISe, 157, 27g. Ml. 2ia, S15, mil, 317, 318, 320, 321. 322, 324, 43S, 4.11, 454, 457, 458. 450, 401. 462, 471, 402, 49a, 50e, 53S, 588-588. T7. 819-828.

Aitdeaiteof KoallaHUls, Colorado, dpseriptiunof

285- 291, 303-30&.3TI>-382, 384-385

analysea of 331

Andcaltlc tuffs of Nevada County, Cal.,

description of IHLIIU

Andovfr. S. Dak., artesian well at 020, 021

analyses uf artesian water fmin well at. 077

Aplahspa formaiioD, eastern Colorado, description of 507

Aplile of Nevada City and Orasa Valley districts, California, ocoorrenoe and characters of 14-4

Appalachian nml Arid, correlation work

in 471M80

Arcentita of quarts veins of Nevada City and Graas Vallrydislriru. ('aliramia,

occurrence of 119

Arkansas Valley in caste Colorado, paper by G. K. O illMrt on nnderground water

of .%Sl-fl01

topofcraphy of. 558- SOg

geology of S0O-58U

Jurstrios rucks of SW-.W

Cretaceous rocks of .'Mil -574

sections acrom <I'I. I.X VIII) 574

upland sands and gravels of 574-577

terrace sands and gravels of 577 -57V

dune sands of 579-580

artesian water of 580-5116

Kmund water of 001

Armour, .S. Dak., artesian writs at 048

analysis of artesian waters fkxnn well at 077 Araeuopyrile of quarts veins of Nevada City and Graas Valley districts. Call

forala, oocumnce of im-iia

Artesian. S. Dak., artesian welts at and

near 834-035

Artesian basin in the Dakotaa, Hmirof. . 070-070 Artesian irrigation In South Dakota, account of OHi-ogo

Arteaian water of a portion of the Dakotaa,

report of N. IL Uarton on OuS-OM

chemical analyst of 070-078

origin of 079-080

amount of OM-OBl

use for power of 830-091

Artesian water of Itliaoia, account of 785-818

geologic sections showing course of 787,

702. 797, 811 geographic and slratigrapUo diatribationof

mi-ao3

anatysca of r27-838

Artesian water of the Arkanaas Valley. In eastern Colorado, uccurrance and char-ants

of 880-5a5

chemicjil analysesof &88-.580

Artesisn water of the Dakota sandstone,

preasore sad bead of 086-070

Artesisn wells, mode of ooastruction and

management of 091-004

Artesisn wells of nilaois, seconntof 785-818

geologle aectlons showing course of

water supply of 7K7, 792. 797. 830, 831

geographic distribution of 801-.Ma

S52

Index.

of MXt-'OM

Ittliiilalwl alata nini-iTuInK HUi-KlH

iif wa't'rn of K27-828

Artt-nluD tkcllaof South Dakola, IrriKallon

frtiui Ml -aw I

fur wattT poMi r of III0-6DI

Aalituu, S. Dak. art en lull wrIU at 91':;

lnuf 228

Angitt hornWrmlr gneliin, Silver Cllir ami U'Mit* Hill*, l/olurailo, doHTiptluii

of g77-TK

i, aiuilyiuHiof 18

Augite j<-nlU' of South Wolf t'ri-rk. CSrars Vnltpx , Cal., lUwriiilion ami anolyaia

of flfuu

Aurifrninn (rrarrU of lh Clly and Ursait iliatriru. California. At-

ft7,Hlfl

Anrorn Couuty. S. artralan wvlUio. 042-043

rt<-*iati irr isatlou In 082

All Saliln SpriOK". Itlinoiii,acoiraBt of TOO

llaciililM comprvoana, flipire of (PI. LXII) . SM Balgrr Hill vein. Uroa* Vallry, Col., d*-

rriptloD of 222

Balil Mountaiu. Colorado. goloKy of 34$-34S

llald Mounlalo darltt-. Culonulo, oecarrinr<>

ami rharocterof . 286-2WI

ami <'I<*viiilim of 14

diaiMaeand areaof atMll

Calavera* formal ion iiMr

Vfinaof

Ilanl. S. Ilak., arteaian arlN uniir

Ilaaalt of t'oluraaltt, cnrrvnce and charac-

t. rof 3I£<31S

Roaita HilU, Colonwlo. by 413

Baoairk aKKhinivrate of Koaita HUla, Colorwlo, cbanu'tcrand grologiral poaition

of 307-111

liamli'k HUl. Colorado, rock* of 3iiS-3Sg

Uaiutick lalop, lEooila lillln. Coloriulo, draeription

of rockaof MyaOd, 430-43fl

cruaa Mllon of or* boily In 434

aaalyala of ore from 43.1

grnMla of orr of 43&-i:bi

Bradh-County. .S. Dak.. art*ian wrlU in. (KS-d'M

iiLrt4alan Irniiatiou In 6g3-atU

clean. E. F., riteil 16

lU-i'ker.Q. F.,clli!<l IM

Hrd rork aerifii of Nevada City and tiraaa Valley dialrieta, California. clMcrlp-

Ifraeoiia roika of. :Ci 7H

Ktdlnieiitary rmks of 7H h'.i

Kfiulijciriil hintiiry iif lIKi-liii

nellefoiiutaiu vein. Nevada County. Cal..

dearrlption of IM

Ilepton cnjiip of eaaterii Colnrailo. ilearripli

..Dof Mt-tM

Pace.

itlc Mnddy Kivi-r, Itlinoiii. ileacriplion of.. 717

Hinuarrk. N. Dak . armenian wellal 063

Dlat'k L4'<l|:e vriim. <;raiia Valley, Cal., work

on 2U

niark pboapliatea of Teonaaoee, cbararter

ami oivurrenre of .'>23-i.13

origin of iM

nUke, W. P., cltrd m

Bliio MounbLiua. gikeiaa and

granite iirraaof 336-337

giwIriKy of 430

llonhoinnw County, S. Dak., artesian wrIU

Ui-Sm

irrigation in SA4..4US

Bonllla, S. Dak., arteaian ni-IU at 63}

Bowlder and UufliJo Hunter Mill, Silver

CUlf, Colo , vhani lcr anil hUlory of 417 Itowlilerminn, -SJIvor Cliff Colo., deocriplion

of 4S2

Bowery vein, Uma Valley, Cal., dcacrip

Uon of gl

Bon bier clny of llliniilK, aci ouotof 766-767

rtowliler lone. Silver Cliff, Colo., drwrtpof

2M 'J9. 403-403

nrercia, diabaae. and |Mirphyr1te araa of Hill, (iroaa Valley. Col. decrlption

of 73-74

Ureoela phoaphate of Tenneaxer, occurrence

Britton, S. Dnk . arteaian well at. 630

Brown Cuanly. S. arteaian wella lu 617-61!)

artexian IrrlKnllnn 10 685

Hroiirn Valley, Minn., arteaian well al . ... 673 Bnile Connly, S. Dak . urteaUn nrella In. 643-645

artenlan irrigation in 88S-6M

Col., deacrlption of a-.n-OTi

Bmnawli k niim-, KevaiLi County. Cal.. ana

of achlatooo near. . Ji Brtuiawlck vein. GrOMi Valley Cal.,dearrlp

tion of rm-Tan

flKiire alionrini: vrnaa aerlion of 230

Burkeye vein, Nevoila County, Cal.. de

arription of

BiiU-DominKo mine, Bine MountalDa, Col

orado, biatory of 414

ronwnlralion plant of. 440

of 441

dla-rani allowing plan of 441

mode of oct um nee of ore 441-443

rhanu-'trr nt' ore of 443-444

funu of ore iHidy of 414 415

Kulliou vein, tinuiK Valley, Cal.. denerip

tion of. , 2il

Banker nudralte. Roaita Hill*. Culonulo, de-

Kriptiou nf

Hunker HilL Colorado, rorka of 371 373

CailmuA mine. Nevada City, Cal., work on 21£ Calaveiiia fumiiitiun, Nevada City and tirnaa Valley ilialriita, California, dlabaae and iHtrpbyrlie dikca of. 00-70

Index.

dctH-riptloD of ISmlia

fuMiU of 71

CaU-itar gnlitinarla vWnaof and (iraiui Talk'}', CaU occumoce of 1 It-US

Caledonia rrin, Xnvaila Cimnty. Cal., doarription

of US

Califurnia. iinMlu<-tiun of M

California mine. NVvatU City. Cal..dK-rtp-lion

of 3m

('amhridisp rdln. Cnu* Vallrr, Cul.. dntcrlplion

of m

Campbell, M. 11.. nut] Mniilvtihall. \V. C.. paper on M't tiun aIniiK tli Kew and Kanaw ha rivers. Wot Virglflla,bv 473-411

Canada Hill area. Kxroda Counly . Cal.. Cal

arrraa funnalion In 83

Cana4ia Bill vein. Xovada County, Cal.. de-vertical

Ion at lltt

diagram nlioinns faolta on 107

Carbon Cliff. III., rwoni of well borioK at . . 849

Carlile Klial> of viil<-ru Colurwlo, foaaiU

drwription of SfiS-SM

Crntrnnialmiue, Oraaa Cal.. dearrip-

North Star rein. Urao* Valley Cal..

deMTiptinn of HI

Cbaliniile of Nrrada City and Urans Valley dislricta. California, or'iim'nm of US

Cbalordonitr of Kold qiiartz vein* of Nevada City and (inua Valley, Cal. ocourronceof 114

Cbalropyrite of <|uar1i vein* of Nevada City and Oraaii Valley diatricta. Call fornlii, ficcurrvni e of Hi

ChamlM'rlain, S oella at nod

near 844-84$, aW

aoalyaU arteiau waUT from well at STT

Chamlwrn'ft Hinelting fnmare, Silver Cliff.

Colo., chararler and liistnry of 417

Champion mine. Nevaila City, Cal.. dew'rip'

tion of 2U=215

Charles Mix Cunnty, H. Dak..arteaian wells

in '. 845-847

artesian irrigutiou In 088

Charleatuwn sandstone. Wnsi Vlrxinia. dc

eriplion nf Sott-.VW

Cbarannat vi in. Nevada County, Cal.,dearriplion

of 110-198

Cheink'alalleratiuu of rurkaof Nevada City and Umss alley diatricta, Colorado, description uf 148-157

6Z i, 68, 67. 68, 71. 7S. 7H t-l IW. l-'l. 11-J. rj3.

iw-irr. 131. i4i>, Iji'. loi, 1-Vt. m. i5.

43.'>. 4ol . 4St, 417. 45S. 400, 461 . 482. 483. 471 , 4S2. 4M, am. S3a Si4x.jW. 877. 7*fi. 8 io. Blg-TOjl Chtrao outlet uf Luke di-rip

lionof 711-712

CUorlnatloo proeesa of milling ore*, de-ai

?riptlou of Si

work on 234

Cinnabar of <iiiartz veins of Nevada City and (grass Volley districts, Callfor.

nia, on-nrrrnce of lift

Clark County, .S, arlexian wrlU In. 823-824

Clandet, K.,rheniiral analyses by l'Ji>-127

Clay County, S. Dak , nrtesinn well, in . . . 6j7-*80 Clay (sllloeous). Silver ('110' and Ibmlta

Hills, Colorado, descriptiuu of 310-320

Clays uf Nevaila County, Cal., analyses of . liS Coal In-ds of Appalw lilac region, work on

com-lsUon of 479-480

Measiin-s of Illinois, alilludw uf 791

Coe vein, (iraas Valley, Cel., di-MCrlption uf . 222 Odonwlo, pii|>er on Keoluy of Silver Cliff

and K'Miln Mills of 283-403

paper by .S K. Kinniiin'i ii mines of. . 44t3-47S Culorailu (eaatrnii. by (i. K. liilltert

on iinderproiiml water of

topngrnphy of j.>8-680

Cvuloi:yof .lOO-SM

Jurat has rocks of 560-581

Crrlaceous rocks of .'<81-574

upland aanda and gravels nf '>74-577

terrace sands and Kfavelaof 577-S79

done aanda of 579-iaO

artesian walrrof &W-j8i$

KMUud water of Ml

Columbia. S. Unk., arleaian well at 818

Ciui'unl IliU. ColnnMlo. rocks 378-3T0

S. Itak., arU'sian well at 623

Cuni;lonierallc phosphate uf description of $2A-S37

(Jonstitution claim. Nei-wia County, Cal.,

vein of Iffl

Cooley. L. E. , citeil 738. 737. 738, 742

of Nevada City and truss Valley

diatrlels, Cnlifomia. iscurrenre' of IM

Creaceut vein, Urass Valley, Cal.. bastion

of 218

(*retaceoua forrnationa nf eastern Colorado,

desHrrtptlon of M1.A74

diagrammatic aecliou nf i7t

diagram slowing formations of 571

descripl ion of Ml-fi74

Cripple Creek. Colo., ore dt-pfisits nf Silver Cliff, Colo.. couiMtri-il with

of 489-470

Cioas, Whitman on E<'loi;y of .Silver

Cliff and the Kosila llilU by iKUVa

serpen tlneiiri'aof g£

Crown point vein, Crass Valley, Cal„ de-of

231-238

Cunnluishiira, A. A., chemical nnslynisby tH-ISl!lO Custer County, Colo,, ,S, K. Kmniuns

uu uiinex of 4u73

l.

Uaclte of Itoslta Hills, Colorado, deaeriptloti

of 2DS-2g6

iM-currence ami oliararter uf 344

Index.

Diikote (rmip of eMtarn Colorado, daacrlptluuof

iet-txt

Uakotk aaadittuue of eutarn Colorado,

water of M2-M6

barton. X. H.. prcltmlnarjr report on artlas watera of a porllon of t ho UakoUu

by ata-m

Paubrtc, A., elted li

Daranport, Iowa, record of drIlUnca from

wrlljiat S4S-84S

IHtTiaon CooDtjr, 8. DaV art<-alun well* in 6I1-4U2

Darla'a McUnrology, cited T23

Day County. 8. Dak., artaatan well* in tU

Doadman'aFlat, Nevada Couoty. Cal., vein*

of aai

Dradwood rein, NVrada CouDly, Cal., da-

DvoompoaitioD of rocka. Silver OliT and Ro-

QOU of .tllUTM

tionof li=li

flirore abowiDK nbnitcd in

IWr Crwk bain, NVrada County, Cal.,

gold-qoartx vrinaof IHiV-iai

Dogrool. citri 22

Dplmant, 8. Dak.. artnUn well at 648

Democrat Hill, Colorado, quarla-aliialtc

of 314-315

rocka of 377-378

Denvrrand RloUraade llallruad, hiatory of

HmeU 8. Dak., artmlan well at 427. 071

Dca IMaiiK'K IlUDoia. diorlptiaD of.. 713

mfaaurvfiK-ntii of 740-742

DevlU Lake. X. Dak., arteaian well at SOS

Dovoniaii limfatou under Rock laland. 111.,

and vicinity, arcount of

of Xeyada County, Cal,. character

of ao-cs. i;.2-i:.3

aoaly Mw of 4, M, 87, 153

DIabaae'of SUvcr ClUTand Roaiu Hilla, Colorado, occurrenoe and character of. 382-283 Dialuwe and {torpbyrlte rock* of Neratla

County, Cel.. da<'ripUoD of BAsJS

Diamond vein, Orau Valley, Cel., deacriptinn

of J51

DicklnaoD, X. Dak., artralati well at . . 862. 883. 654 Dike rocka of Siln-r Cliff and Roalta UIIIji,

Colorado, of 280-284, 382-383

Dike* of Nerada County, Cel., deacnptiona

of S8-80. 04 65. 08 '0.74-75

Diorite of Xovwla City and Graaa Valley

diatricta, California, oooumince aud

cbaraotcrof iSi=Al

Dinrite of KoaiU Hilla, Colorado, dMirlp.

tion of 291-296

Diorite-gabbro-peridotitn group uf rovka of

the Sierra Nerada, oocnrreDi-<< and

character of

Diorite-porphyrite of the Nerada City and

(raaa Valley diatricta. Califoniia, oo.

currence and rbantcter of iZ

Dotaad, S. Dak., artaalaa well at (33

analyaaa of artealan water tmm well at . 677

Doracj, Victor, aeknowIedfnBeata to m

Dmiclaa, E.M., triaugalaUooby 11

Doaglaa County, &. Dak,, artalan wella

artaoUn Irrigatlun in 6M

Drift of lUlDoU. walla in 776-781

topographic eihct of TOTU

tbiokncaa of 707

Drift mining, proceaa of B

Dramedary -Granite Hill vein, Grsw Valley.

Cal., dearription of 23.S-a36

Done Minda of caatrn Colorado, deaeriptloD

of t74m

water of SM

Dunnlngtoo. A, F,, topofpraphic mapa pre.

Dury-e furnace. Silver Cliff, Colo., cfaaracter

and biitory of 418

Dutch Flat. Colorado, rock* of 356

E.

Eagle rein. Kerada City, Cal,, deeeription

of aa

Kaklna, L, work of. IB

analyaea by

3S1. 31S. 316, 317, 318. 330, 321, 323, 334. 4M. 471 Earlvill, 111 . (lowing-well district near - . 77-780 EaatUoline, III,, record of well boring at .. 848 Eaat Pierre, S. artemaB well at — 629-630 Ebangh vein, Nevada County. Cel., detcription

of IM

Edgeley. N. Dak.,artaiiin well at 662

Edmnnda County, K. Dak., arti-alan well*

Elk Point ,S. Dak., artecian wella at 673

Ellendaie, N. Dak., arteaian well* at 661

tion of Si

Emmona. 8. F., work of aog

Empiric mine, Valley, Cal., rnioa of,. IM

of 3a2s2Sa

flgiired allowing fault at 253

Kmpire-Oaborce Hill vein yates, OritaK

Valley, Cal.. deacriptlon of 2Uz2&2

Eoglebright. W. F., acknowlodgmontA to. . . 12 Eureka mine, Graaa Valley. Cel., d-arriptionof

221221

figure ahowlng aections in SiSiZZZ

Eureka, Idalao Maryland rein. Graaa Valley.

Cel., deacriptlon of 221=23

Excelaior Ridge. Colorado, rocka of 173

Fablers of qoarts vein* of Nevada City and Oraa* Valley diotrlcu. California, ocoorrena-e of Hi

Fair Ground, Nerada tnty, Cal.. diorite

of -W-Sl

Fairriew dIoriU'. Koaila Hill*. Colorado.

deacripdonof 291-29lk

Fanner City. 111., flowing well* at

Index.

rHUkCiBty,&IMt..artcaiaiiwdl*iii.. a24-3

tU.

analyaU of aiteaiao water frm wM at. 677 VanlU Id Nevada City and Oraaa Valley

dUtrleU, California, oeenmMoa of. . IflO-U" Fajretto aaadatoDC, Wvat Virg inia, dMcrip-

Federal Loan mine, Nevada Couaty, Ckl.,

dikealnargilUteaof M-flO

Calavaraa fommtioo at 80=82

anaJyaia of wall rook fhaa fil

mineral waters of 121

rein of .. I8.|ir7

vertical uction at 187

Feldspar, bydro-rbMnieal proeeaaee of alteration of 88

Flrnuao. Poter.cbeoitcalaBalyala made by. 13,

Fiasan.-*, ore bearing, of Roalta mine*, Coloiwlo

, description of 423-138

FlMnree and vrina, cbaagea in Sierra Nevada rockK doe fanaatloD of VSL

Tiaaare yatema of Nevada City and Oraaa Vall<*y distrirte, Califomia, relatiooto

Keologir. iitractarti of IW-IM

origin of UBaHl

drMrljitliin of 14.171.4> l

Fleoebarg. .S. Iak.. arteeian wella at M '

Koiilaine,W. M..i 482. 4M i

Fureat spring group of minv*, Grai Val-

Iv.r, Cal., deurlptlun of ?lft.'j47

Fort Dak . artealan well at. . WO.472

FortSnlly.a Dak., artesian wella In 831

Fos IlilU group of eaatem Colorado, description of 68D

Fox Klver, Illinois. description of 713

measuvmrnU of 743

Frankfort, S. Dak., arteaian wella at 822

Franklin HuMiry vrin, Nevada County,

Cal .dearriptloD of im

Franklin vein, Oram* Valley. Cal., dearrlptlon

of 261

Frederick. & Dak., artcaian well a 1 818

Falton,& Dak., artesian well at 871

O.

Gabbro of Nevada City and Oraaa Talley

diatricta, occarreoco and charactera

of &i-a

Galena of qnarts vrina of Nevada City and

Graiix Valley diatricta, California, oc.

eurrence 118

Galmia limeatone under Rock Island, 111.,

and vicinity, account of 836-838

Uamet of NrvBila City and Oraas Valley

diatricta, Califoroia, occurrence of. . . 121

Came lUdge, Colorado, rtM-ksof 3SI-3S5

(tame KMgo MUl, .Sliver Clill; Colo., deacrlp

tioD and hlalury of 410

Gangue minerals of Nevada City and Oraas

Valley diatricta, California, syntkeals

of 178.1711

Geikia. A . ritcd SiMil

Geyser nine. Silver CIliT, Colo., descriptkm

of 3Wk39K

rage.

Oej-aer mine. Sliver Cliif, Colo., deep

country rocka of . 4M-4M

orabodleaof iS<

vein materials of 498-438

analyses of ore from 457

aoalyaea of earthy vein msKrial fram.. 4S8

water course* of 4S4

analyaea of siutera of 490

analyaea of waters of 480-4A1

Geyser Mining and Hilling Company, Silver

CUff. Colo., work of 490

Gilbert, O. K., paper on niMlergTunnd water of the Arkansas Valley in eaatem

Colorado by UI-801

Glacial drift of Illinois, topograpbio elTect

of 708-711

of. 707

wella In 7M-7t

Gleooee Gracle vein, Nevada County. Cal.,

deacription of

Gneiss and granite of Silver Clilf and RoaiU

llllla, Colorado, description of 'J7S-

2W, 333-338, 384. 398-399

Oold, California production of 2ft

Nevada County, Cal., production of

from orca of Nevada City and Graas

Valley districta.Callfornla U&-IH 134

solubility of la

Gold of Nevada City and Grass Valley dla. trirta, California, mode of precipitation, depoeitloD, and occurrence of. . . 181-

Gold and silver production of Custer County,

Culo., table showing . ... 430

Oold Flat vein, Nevaala City. Cal.. deocription

of sub

Gold HIU Kocky Kur relo, Grasa Valley.

Cal., description of 23:i-284

Gold Hill, and Maaaachuaetis Hill, Craaa

Valley, Cal., description of veins of. ro-M

Oold Point vein, G raas Valley, Cal., deaerlptlon

of 2Sfi

OoM-quarta veins of Nevada City and Graaa Valley districta, California, paper by WaMemar Lindgren on... 1-381

character and occurrence of iis-iia

nlneralogy of lli=12ll

mineral waters of

Gold Tunnel vein, Nevada City, Cal., dascriptlon

of 287

Graneroa formation, Colondo, deacrlption

of 984

Granite and gneissofSllrerCliir and Boaita Hiila, Colomdo, ehamcter and exposures of I70!!5.iK-''M.M

Granite Bill-Dromedary vein, Crasa Val

ley. Cal., deacrlption of 23S-238

Oraaltaporphyry of the Nevada City and Graas Valley districts, California, oi'-

curreoce and character of

analyala of

Oraaodlorlte of Nevada City and Graaa Valley districts, California, occurrence

and character of 38-44

chemical analyais of 39. M

Index.

Gnmodlolira (altcml) of KrvaHa VMy Mill UnuM ilialrirU, California, dnniptian

of latJil

analjrMa of 141

Grant rein. Nrvada ConBtv, CWl., dracrip-

GraiMi VallK.raodKrTadaCitj'diiitri'-ta.Ciilifornia, paper by WaMi-iiiar Lindgrvn

on 1-302

location of 18, 2M

topography of UU

vegetation of U

litrrntarr conrrmiDg 1&-17

history of 17-18

mining ami milling In 18-2S

colli nnil ilrerpnxtiictlonin 228

jtfncrnl Keo'ogjof 89-3i

edlmentnrr Ixxl nxrka of . 7l>-HB

njclamorphioin in iSLSi.

fomationa of <W-im

geological litiitorjr of

arm of 112=li4

rock rhanice* ilii to AMuro ami rrio

formation iu 1I&-157

win atructnre and paj aiioota in liftiffi

tluara ayatema in ifti-iTi

temperature in mlnca of , iTft-iTi

geneata of Teiaa of ITlftt

detailed dcacrlption of llCi-257

anmmary of goologjof

pay ahoota of JSl

Oravel* caatcm Colorado, doarription of S77-S7I>

Orarela and sanda (upland) of eoatcm Colorado, drarript ion of (>74~57T

water of MKJ-JB8

Oroenhom formation, Colorado, deorription

of WW-S6S

Grpcnman vein. Nevada County, Cal., doacrlptlon

of lifi

Greenwood. S. Dak., artenlan writ at <ue

Orotoli, S. art'aian wclU at 618

tirunnd water of tlio Arkunnaa Vallry iu eaalem Colurudo, ocmm'ni'e and character of 50&-401

H.

Hague, Arnold, cited 2QS

Hamiuoud.J. H .i ilnd SI

Hand County, !4. Duk.. arteHlan wella in 837-

artealan irrigation In

nauwiu County, S. urti'alan wella in . 6.18-040

Harold. S. Dak., artesian well at KM

aualysia of artoitian water from well at. 677 Hartery mine. C, raiu Valley. Cal.. vein!) of . 2az2il HaMell anti llyi-r farm, Spink County, 8.

Dak., artesian Irrigation on GM,

Hayea, C. W., on Tenneajiee pfaoaphateiihy

Sll-StS

HermuMi vein, Gruaa Valley, Cal., dcM-rlp-

t ion of laa

IletcnM-eraa nrliraiH-rnae, flguru of (I'l.

Pagoi

Heaaton vein, Graaa Vallry, Cal., deacription

of m

Ilighmore. 8. Dak., artesian well at ttt

HUlebraod, W. V., cliemical aiuklysn made

by 13.W.42.8I,12L122.H3.

126-127. Iso. 4W, 4S0, 461. 463, 44B, Mi8-Sw

cited 122. SW

Hlnton formation. West Virginia, description of 487-48B

Hitchcock, 8. Dak., artesian wells at and

near 825, 971

analysis of artealan water from well at 677 Home mine, Nevada Oiuut}', Cal., section at SI

velnaof 21g-21

Homeward Bound mine, Graas Valley. Cal.,

work at 211

Hudaon River abate under ItiH'k Island, III.,

and vielnlty, aoiiiint of fCI4-KI3

Hnghes County, 8. Dak., artesian wells in 62S-630 Humboldt mine. Boaita HiUa, Colorado, deacriptlonof

424-428

Humboldt-Pocahontas vein. RoelU nUla.

Colorado, devaJopment of 412

deserlption of 423

figure showing elevatlcm of 426

figure showing cross section of 427

Hunter farm, Spink County.S. Dak.,artelitn

irrigation on 6iW. 889

Huron. & Dak., artealan wella at 625-028

niialyalaof artealaii water from well at . 877 Holrhina4in County, S. Dak., artesian wella

In 64IMU0

Hyde County, ,S. Dak., artealan wells in ... . 629 llydrnulic mining urar Nevada City, Cal.,

hiatorj-of U

propMa of 2X

Idaho mine. Grass Valley, Cal., deacriptlon

of 224-229

Idaho system of vrtos, Gisss Valley. Cal,.

deerription of 991.1X1

Igneous rocks of tho bed-rock series of Ibo Nevada City and Graas Valley districts, California, description of 3S-76

nUnoia, pa]>cr by Frank I.everrtl on water

reaonro'sof 606-849

pbyalcal features of 703-717

rainfall of 718-729

run off of 730-743

narigablo watere of 744-74S

water power of 746-747

water supplies for relies and villages

of 7*H-764

water supplies fur rural diatrlrls of. . 76&-7M

artesian wells of 785-818

analy<'s of waters of 811828

Paloozoic rock* of 839-849

lUiuola River, description of 7I2-71S

meaaiirentents iif 7I&-742

Illinois Vermilion River, description of. . 713-714 ImiM-rial veins. Graaa Valley, Cal.. description of

Index.

Indiao Flat. Kevada Conatr. Cal-, Mrpen-

On*- ure* of

anaof 7*-77

lukeniuinn vein. Grmw Vsllvr. Col., deaerlp-

t ion of 234

Inocrrmroin Jfi'iTnU, flpirr* of (PI LX) SM iQuceramnii UbiatiM. flfnrea (I'l. LVII). &AS tiMKvramnx wusruiiiii. flKtirv nf LXVIi . 572 lutnertinn of vrliia in Kerada Clly and

Oraaa Vally dlatricts, Califarnia. occarrr

Di-rof IMt-lBT

Ipawicb. S. Dak., artMlan well at 619

analysis of artraliui water from well at. flTT Iiiah- American vrln Oraaa Valley, Cal., d-

arriptinn of 33fi

Iran Hill, Colorado, rocka of 175

Iron aulphidea, nt-rurreDcvand formation of. iiasit& InKjuols, 8. Dak., analvais of artealan water

from well at 7

Irnqiiola County. Ill . flowinB wella of. .. 773-77 Initiation (artesian) In South Dakota, ac

<:ount of 09I-89O

lUlkau vein. Nevada City, Cal.. deseriptiou

of 2""

J.

Janie* Cupola Fumwe, Roslta. Colo., desrriplinn

and liinlory of

Jamestonn N. Dak .. artesian well at M2

analysis of artesian water from well iit 077 Jerauld County. S. Dak. .arU'siaii wells In. <t31-<Kt3

arleisn irrigation in

Jersey Blue rolo. t'.rasa Valley, Cal., description of 235

Bull vein. Nevaila City. Cal.. work on. 211

Jolltt, III., record of well boring at

Juratriaa rocks of eastern Colorado, de-

M-riptionof MO-Sei

Kanawha and New river. West Virginia.

IMiptT on jceuliitsic Hectlun aloOK 473-filI

Kanawha furioatiun. West Virginia, dascrlp'

lower I'oal croup of 501-505

Anstel ruia ijf 501-i02

KukIs <'oal of 502

Uas or Coal Valley coal of 502

I'oerlrwi coal of

Ilrnwnslown rual of 501

CampltvU's Creek coal of. 505

UpjM-r group of 305-407

Kanawha l.la k Hint of 07-l!08

Kankakee Ilill, Colorado, rw ka of 370-71

Kaukakw Kivrr. Illinois, deaeription of 713

nii-unuremi-nta 7'I0

Kaskiukla River. Illinoii. description of. . . 717 Kale lUycs vein, Valley, Cal., de-

M-riptlonor 212=2111

Kentucky vein. Gnus Valley. Cal., description of 221

Kinilwll. link., analysis of artesian water

from well at 077

I'age.

Kingabnry Oonnty, K. Dak., art4MUn wells

Tnlns, Nevaila Cnunty, Cal.,

description of IXl

King of the Valley mine. Silver Clllf, Coki.,

description of 451

Kirkbam vein, Nevadn City, Cal., work on. 212

KnlckerlKK'ker Hill. Coloral", nicks of !r75

Knight, F, C. chrmkal analysis by 4SS

Lafayette and Cmnet vein. Grass Valley,

Cal.. di-acription of SSS

Lake beds of Silver CliflT, Colo., description

of 337 -.138

Lake Uichigan, Chicago outlet nf 711-713

I.,aniarqiui vein. Grass Valley. Cal., description of 238

Lamellar phosphate of Tennnaee, occurrence and cliaractrrof &40-MI

Laogfonl.S. Dnk.. nrtMlun wi-ll at BJ!0

Lawmn. A. C. nrknowlnlgments to lU

I-avenwortli niiiu-. Knsita Hills, ColoriMlo,

di-scripting nf 428

Leaonipton vein. Nevada County. Cal., de

scrlptiun of IBT-llM

I,es<|urreui, L., California Neuri-ne flora

examined liy Ufl

Letcher, S. Dak., artesian wells at and

near *33, C34

Li!vant claim, Nevada County. Cal. .rein of. lH

L-everett. Frank, on water reaoiirccs

of Illinulsby e05-4S

I.kuburglte of Colorado, occurrence and

character of 3lt-3U

Limoniteof Nevada City and Grass Valley

districts. Call furo la. occurrence of lift

Litidjpren. Woldemar, pa|>er on gold'<)marta veina of Nevada City and Grasa Valley districts. California, by 1-MS

Little Deer Creek iHisio, Nevada County.

Col., description of UUIS

Loew, O.. rlieniical analyse* by IbW-MO

Imoc Juek mine, Grass Valley, Cal., work

at UUtt

I-uokoul Uountulu. Colorado. r<!ks of 374-375

lAiwer Magnesian tlrarslone under Rock

Island, HI., and vjrinity.accnuiit of.. 839

M.

>lBcklnaw RiTer, Illinois, desrriptlon of T14

Macoupin Creek, Illinois, description of 715

qnencr and liflrrnntiatiou of 33K-331

Magnesite of vrinn of Nevaila City and ttraos Valley, (.'al., occurrence of 11&

Magnctiteof Nevaila City and Graas Valley

districts. Califoniu. occorrcnre of . .. 12ft Mallet Lixiviation Works, Kootta, Colo.,

descrijilinn and liUtury uf 416

Mandan, N. Dnk.. artesian well at Wi. Mi

Msngsnese ore uf Nevada City and Grass Viillrvdlslrirls I 'olil'arnis. iH ciirrcncf nf...'. 12a

Index.

XMihatUB Tela, NeraiU City. Cal., daacrlptton

of am

IlaoauiiU mhkf. NeTada City. Cal., Melkm

of funnationii at

llarraait of qiurti of Xerada Clly

and Gnwa VaUj diatrirta, CalitafBla,

oc<-nrTMicof in.iia

MarraaWB farnatioo. Colorado,

oocuiTfiDce of MS

Maripoaa formation. Nerada City aiul Oraaa

Valley diatricU. Callforela. deacrip-

Uonof

If arlpmitc of Kold-quartx Trio* of Nevada

Ctly aod Gnua Vallt-y. Cal.. oocorreoce

of 11&

Marahall, J. W., dlocovery of gold in tba

Sierra Nevada by 12

IfarntiBli. R. B., topoinpliic maps ptvparcd

by IS

tine area of fa-iA

dialiaae dikea In erpenilue of AS

diabane of BMW

dewrriplinn of Tli Tft

fiiriirm Khowliig cnuw aertlon In

MaMaclmaetta nUI. Valley. Cal., drcription

of veina of . gft-gMt

Mayliuwer compli'X uf vrluii, Nevada

CiMiDty, ( 'al.. dtwcrlptlou of IBA-IM

Haydower mine, Nevada County, Cal., vrr

Heal aectlona at UB

HeCook County, S. Ilak.. artMian vrelU

Mead, D. W.. acknowlrdgmento to 702

Medora, N. arteitiaD well at ... . M2, 063, 6M

Meek and Hayden, cited 6W

Mellette, S. Oak., arteatan well* at 8ZI

Melville. W. H.. chemical analyse* hy

rryntallocraphlo dotermlnatlona by ... . 317

Mcnito, K. Dak , arteaian well at 872, S7A

Mcsdenhall. W. C . and Campbell, M. K.,

paper tin Kmliidle aertlon aluns the

Mew and Kanawha rivero, Weat Virginia, by 473-SIl

Merrilield rein, NevwIaClly, CaU.,drMrl|>-

tionof aoa-aig

Merrill. P.. eltad Jfi

Merrimac vein, Nevada City, Cal., di-acrip-

I Ion of Mft-aw

Metallk' uiinerala of Colorado ulnea. aoiirce

of 4T0-47J

Metal* of Nevada City and Craaa Valley

dintricln. Callfmula. origin of 174-17S

Mctaniorphian in Nevada City and Uraaa

Vall<-y dlatrlcla, CalifornU. driptlonuf

SfLM

Micadarite of Colorado, occuireocc and

character of 311-113

Midnight vein, Nevada City. Ual.. work

on SQftJllZ

Milan. 111., raoord of well boring at S46

Millbaok. & Dak., arteaian well M. 671

.Ulllrr.a.

aualyala of artaaian water from well at. S77

MllllDgofaM*, .i 'i

Miawr Comity. S. Ilak.. artaaiaa woUa in m-tn arteaian Irrigation In W7-M8

Mining and railllng In Nevada City and Graaii Valley diatricU. Caafomla, proccaaeaof XUft

Mining clalroi In Nevada City and Onaa Valley dlatrlrU. California, detcrmlnation of extent of M.M

Mine* of Cnater County. Colo., paper by

S. V. Emmnoit on

Mluea of Nevada City and Graaii Valley diatrirta. Califonila. in. . . 170.171

MiMianippI River, njraaun-menta uf 7SS

Mitchell. S. Dak., artenlan well* al MS

Mohawk Tfin, Nevada City. Cal., dewriptiiin

of 2m

Mobigan vein. Nevada City. Cal.. dmerip.

tlon of 2!&

Molina. III., record of well boring at iU7-M(

Molybdenite of quart! vein* of Nevada City and Uraaa Valley dUlricta. Callfumia, occnrrenc* of m

Monroe, C. K. , chemical aualyaea by SM

Montana vein. Nevada County, Cal., douriplinnof

laa

Monntainerr mine. Nevada City. Cal., mineral walcrB of Hl-IM

Monntaincer win. Nevada City. Cal., de.

acription of aiMUTna

Meant Auburn mine. Nevaiia City. Cal.,deacription

of 213.

Monnt Falrvlew Colaradii mckx of 37g

Mount George Claim. Nevada County, t.'al.,

deacriptton of 2U

Mount Robtnaon. Colorado, quart! ainnite

rock* of 3IJ-317

rockaof 3M-3ao

Mount Tyndall. Colorado, rocka at 3aZ-M8

Mnrchie veina, Nevada County, Cal., decriptlon

of mi

Muacovltiied rock*. RoalU Hllla, Colorado,

deacription of 3tt-32S

N.

Neocene bed-rock anrface of Nevada City and Uraaa Valley diatriola. dearript Ion

of lOft-lOa

Nevada City. Cal., Hgore of aection of b nil

at

Nevada City mi nr. deacription of al&.2l7

Nevada City and <;raiia Valley diatrirta. Callfiirala. paper by Waldrmar Liudloeatlonuf

IX 2U

topography of H.1S

vegetation of 14

Ularatureroncemlng 1&.17

hiatory of 17.111

mining and nlUlng In 1-M

gold and allver pnidnctlnn in M-M

geoeral geology of.

Index.

Vvrada CHy and Graaa Valley dtitiieU,

Calirornka, iKneooa bed rorkaof a&sZft

MllmeuUry bMl rock* of Oja.

Culavcnu fonuaUon in isi

iDttUmorplilaui in

Stiperlaceot formatioDs of 97-101. 2fi2

CcoluKlcallilitoryor "n*-"'

tork changM du to flaanra and rvin

fomuitlonln M&-157

Tela utrneliiro and pay thoota in 158-13

llaaure yafa-ma in 184-171 ZM

temperature iu mlnea of 170-171

gpDcaiK of Telna of 172- IM.

delallMl dracriplion of 1X&-257

anmniary of gcolngy of 25-aM

pay ahoota of 241

Nevada County vpln, Nevada City, Cal., deaeriptlo

D of 2Itt

Ifever Sweat vein, Nevada County, Cal., deacriptionof

U8jfie

vortli.-al seel Ion along in

Nevada County. Cal., gold prodovtion of 2ft=2£

ITewark. Dak., arteaiau at 6IB-83D

aiialyaia arlealan water frotn well at 077

Newell. F. H . ac knom lwlgmrnta lo flOl

New ami Kanawha river*. Weal Tirfinia,

paper on Eeolosir aecliuu along 473-Sll

New Itocky liar vein. Craax Valley. Cal.,

dearription nf 231

New Tork Hill Graaa Valley. Cal.. deerrlptuna

of veina near 2:i6-'.'41

Niagara under Itock lalaod, III.,

and vi. inlty. account of 834

Niobrara group rnatem formationa

and foaaila of SM-MT

Korambagna rrin. Graaa Valley, Cal., deacrip

Uon of 248-247

llgurr ahowing vrrtiral aerlioo along . . 248 NaiinaiHli veina. Nevaila County, Cal., derription

of JSI

North lianni-r veioa. Nevada County, Cal.,

dearriptinn nf 19iUliK>

North Uakota, arU-aian walera of. <loa-l7, MI-MS

arteelan well* In MI-MS

aecliun M3

North ,Star mine. Graaa Valley, Cal., dialaue

and porphyrite area of 70-72

Calaveraa fomiatiun near tg

Teina of Itt

dracrlptloD of veina near 238-141

North Star vein. Graaa Valley. Cal., dw:rip-

Uonof lU-tW

Nortbvllle. 8. well at 621

analyala of artMaD walsh fhnn well at. 677

O.

Oakea. N. Dak ., arleaian well at

Odio drift mine, Nevada County. Cal,, aectloo

at lai

Okaw River, Illlnola, deecrlpt Ion of 717

Omaha mine. Graaa Valli-y. Cal.. work at . 141-143

arctioD at 243

Omaha ayatrm of veina, Oraaa Valley. Cal..

deecriplion of 41->I6

I'flaw

vein, Oraaa Valley, Cal., deaeription

flgnre ahvwjnK aectlon along ahaft in . . 212 Omega vein, Nevada Cautjr, Cal., deai-riptionof

iMulgg

Oolitic phoapbate of Tenneaaee. deaeription

of sz-sat

of gold-qoartt veiua of Nevada City

and Oraaa Valley, Cal., occurrence of. 11

Ophir Hill vein. GnuM Valley, Cal., deaeription of

Ore-bearing flaaurea of Roaitamlnea. Colodeaeription

of 422-42S

Ore niinrrala uf quarti-veina of Nevada City and Graaa Valley diatricia, Callfumia, deaeription of li.'i-llQ

Orca of Nevada City and Graaa Valley dU trieta. Caliromla, character and occurrence of un.iu.

gold of m

value of H7.IM

atroctnre of 12iCl44

Orlaua mine, Graaa Valley. Cal.. quartxporphyrlte

dikea of 74-7*

deaeription of 2S4

(Irleana vein, Nevada City, <°ai.. deM-riplinn

of am

Orient. S, Dak ., arteaiau well at 624

Uro Fino claim. Nevada Clly. Cal.. map and

deaeription of 214

Oahnm Uill. Graaa Valley. Cal., diabaae. imrphyrite. and brec-ia area of

Osborn Hill vein. Gnu* Valley, Cal.. de-

MTiptian of 2SS-2S6

OaceoU veJn. Nevada County, Cal . de-

Ottawa, III., record of well Imringat

P.

r. ii O. mine. Colorado, dearriptinn of rocka

of

Palatine, til . flowing wella near 781

Paleosoic rorka of IlUimla, account of 7M-

Paria Hill. Colorado, rorkaof 376-377

Parltaton, S. Dak., arteaian wclla at and

near Mt.tM

artealan wella at 672.676

Potadain rocka under Rock laland. III..

and vicinity, account of 8-M0

Pay nf Nevada City and Graaa Valley

dialricta, Califoniia, deacriplion of. . ISV-

Peabody vein, Graaa Valley, Cal., deaerip

tionof 234-238

Pennaylvania Hill. Colorado, geology of 349

Peunaylvanla mine, Nevada City, Cal., d-

acriptlonol J07

Pennaylvaiila Rolaetion Worka. Roaita,

Colo., deaeription and hiatoryof 416-417

Pennaylvania vein. Graaa Valley, Cal., deaeription nf 243-249

figure abusing ooorae of 2tf

Index.

of 283

ual.VM-of S04

of 241

Perry Counly. Tmo.. phnsphali* dvpmilit,

dnwription of S31-

Pbwuix-Uary Ann rrin. Grau Vallcr, Ca).,

work on 2ii

Pboapliatcs of TcnoMorf, paioT b.v CW.

Uayraoo

clawiification of SIH-SW

gimcral relattoiu of MO KJ

black M-S-W

white 538-S48

Pterre raalvm Colomilo. bnl* aiul

foailmf 507-,'.

Plrrrw. S. Oak., arllian wrll nt 629

analyaUof artnliin ntrr from wril at. 6T7 PiotM-rr mine, KiMita llilln, Colorado, d-

M-riplinniif 429

PilcbatoiKof .-ilrcr Clitf nnil Itooltu IlilU.

(y'olorwlo, docuftipOMllion product of Sit-XSD

ilMrrlplion of area of 400-401 :

orctirrrnrn and t'baraoler of 396

Pitmliiiri; iiiine, Kovada County, Cal.. dla-

PilUburii vein, N'nvadu City, Cal .dnwriptioii

of 2SS=iS&

flgurm abovrinK rrrtieal MctioBa at.. gWi T*lacenllrera plac-vnta. flKur of <PI.

L.Xiiii 506

Placer nilulUK near Nevada City, Cal., hlR-

fory of IK-IB

Plankluluii, S. wdUal 643

artcniaii well at 671

tiiiii and liitory of 418

PleBMinl Flat, odaCoiinty. Cal.. dearrlp- i

tlon of diorite area of

nralite dlaluiMdiWex of i-6li

Pleinlra-ene deiHMiitii of Silver Cliff aod I Hill*. Colorado. deiH-rlplloD of. 323-

Plyimnith Hill, Colonulo, gwlogy of 344-345

i'oruboiilaa Hill, Columdo, rocks of 35I-3U

Pui'iihuDtttM minp, Itoitita Hilla. Colorado.

dfurriptinn of 4Z;i-424.425

Poiica, Nobr., arti'nian nell nt 672,678

Porpliyrile of llannrr Hill arva. Nevada

rharaclerof 60-61

Porphyrile and dinlMiM Kroiip of rurka of Nevada City and Groo* Valley din.

Iricta, Callfumla, devrripti'in of 5ft. 76

Potoai vein, Nemda Cily. Col., dracriptlon

of ans

of Cniili-r County.

Colo., tal'b* ahiiw Inj; 420

Prlnorlon rale, Wmt Virginia,

desrripliiiii iif 489-48U

I'ringle audealle. Colorado, iHrurreDrn and

rliariK li r iif 303-305. 3HU-3H'.:

l*rkiKle llill. oloradu, ruck* of . . 37l>-363

Page.

IVionnrjrrlna vyomioKeDal*. flgnrea of (Pi.

Lviiu Sm

Providrnrr mine. Nevada City, Cal,, minrral

vatera of iw-im

veUiKtkf. Ui

dtHirriptiott of aW-ZlO. ZU,

Pkiloinelano. aaalyaiit nf 451

P.vrarcyrltcof qnarli vein* of NevailaCily

and Clrao* Valley dlnlrtcta, California,

orcurrviue of

Pyrile and pvrrotite. tiKurc ahofrloK inter

BTowth w ith tllanic Iron ore of

I'yrite of (|narti veioa of Neva4la City and

Oraoa Valley diatricU. California,

oeriirrenco nf IIT

Pyrolualie of Nevada City and Oraait Val.

ley diitrirta. California. o<'currDeef. IM

Pyrrhollie in uuKile. lipnre nhoo lui; S

vada County, Cal-. deiirrlpiion of fd

Pyrrlintlle nf quart t veins of Nevada City

and Graaa Valley dlatrlcta California,

occnrrence of m

Q

Qaarti of veins of Navada City and Graaa

Valley, Cal,. cbarai-leroy II4

anal y iien of m

Ugiire* of thin nerlloiia of. UtlM

Qiiartz-alunite rocks, Roalta Ililla. Colonuln

. dcacripllon of 314-31t

unalyw* of 31S. 316

rot k. aoalyaia of 317

(jiiartz mining in the Nevada City and Grans

Valli-y dislrirta. Calilornia. bixtory ol . iB-?3 dike* of Orlpaos mine.

Grans Valley, Cal., dracriptiou of 74-7S

Qnerida CuKirado. trni byte an-a of 360.361

Qutunimont-FIre Creek euol. West Viripnla,

dearription of

K.

Raa, E. C, cited TtJ.734

Rainfall of Illinois, detaili-d acronni of. . 71-729 Italeigh sandstone. West Virginia, daacrip.

tion of 4B3-4M

Rattloanake Hill, Colorado, dike at 3WI-38T

rocka In vicinity nf 3g7-3M

Kaymond, S. Dak., artesian well near 6X3,671

KedDeld, S Oak., arieaian well at 622

analysis of artesian water fmni well at. VTl Redaction jilanta of Kiwila Hills nod Silver CIIIT, Colorailn, nnnnieration and de.

acriptlon of 416-110

Reward mine. Nevaila Cily, Cel.. descripthin

of 267

Kb.polite of .illver Clilf and Rnsita Hilla. Colorado, occurrence and character

of 296-303,

a4l-:CpO, -.tie. 31*3-384 .THU-.TOI, TIM. 402

mines in 44-i6

anal> sen of diN-mniMKiiljnu prtiduetnof tU Ubyolitic lulls nl the Nevada Cii.\ and Valley diatrii ls Callforuiji. description aud aiialvsia of ag-M

Index.

Kbyoliitc tuff or SilTcT CHIT and the llMlu

tliiU, (.'oIotimIo, orutTeocK of 385-

3M. 391. 308-. RJchardii, K. D.. iu-titan irrl|{alion in IIiim1I>

Countv.S. Dmk.. by wa.mt

Rich Hill veto, C.nt VaUey. Cal.. dnicri|>'

Rivern ami orrrku of nwtrrn Coloniilo, un-

d*rdow of 508-flPI

Btibbln* aud Uyrr Mill, Stivrr 4'Urr. Colo.,

rluirartor Hnd liUlury of 410

ItobiuMin rialrau, <Vlonido, rorka of

Surk Uland. III., and vicinity, account of

I'aleutoic rurku at fl2SMl4e

map abdwInK ItM-atloiia of derp wi-IU at. 829

Nlanra UiDMluur under.

Uudaiiu KIrrr kIuiIp iiodrr 834-H35

(ialena llnutaUuir nmlor SSS~S3&

Tn-nton limalone under 83IMI3T

St. Prtcr Minditonn under 8ai-838

Potadani rix ka under

tabl<> abiiwinK thirkuraa of fomuitiona

under 841

griwraliteil Ktvlaitir Mtion for 843

exauiinstlon of wril drilling* from... 842-849

Bock Rirrr, lUinuin, deacrlptlun of 715-718

nit-aaamncnu nf TSS-Tll

Rogrra. W. B., cltrd 4K7

Rowor. S. Dak.. rK alan well at 019

Kowbiid lodUn KoMsrTation. 8. Dkk., arte-alan

well on 600

Roae Hill veln.OraMi Valley, Cal.. deaeriptloo

of SI

Kofllta andt'aite. Colorado, orvarrenre and

character of 28-388, 34A. 3n>-380

KoaiU UilU. Colorado. ReoloKy of 3-391

aadeaila emption of 339-340

Banker andeaita emptioo of MO

Kald Mountain dacitv eruption of 340-:m1

rhyolitic outbarat of 341-342

rrlOKlo andritib* tlow of 342-343

trai'hytc of 343

BaNMIrk rolranir nm-k of 343

drlailrd dnarriplioo of 344-391

RoalUi Hilla and .Silver Clitf mining diatrlct*. Colomdo. juiprr by XVhltoiau

Cruaa un itmloKy of 3S3-408

blatory of 413-418

rrdnrliun planlaof 416-419

pmdnctiun of 419-430

fona oi on! Uidira of 407-409

Roslta mlnea i.'uluradn, blatory and dearrlpion

of 421-429

Ruaita Retliirtinn Worka, Colorado, character and hintory of 416

fi-renllatJon nf niagniuaol .13ft-331

Ruugb antl tt<-aily, Nrrada County, Cal,,

Tnin of Mft-gj?

Kounil Colnrado, doacriptlonof . 394-38S Royal formation, Went Virginia, dearriptioD

of 489-490

Kun-offof IlllBoia, account uf 730-743

S. Taga.

.Saekett, S. G., aid by 41

SU John mine. Oraaa Valley, Cal., fiacurm

afauwing Tclna in TVi'i'T

deacription of 221

St. Jonepli It -Smt'ltcr. Silver CHIT, Colo..

charai-ter and biatxry of 417

8t. Lawrrnov. S. Dak., artvaian wella at ffiH

St- I.oma vriu. Nevada County, Cal., deicriptiun

of io"nn

St. Petoraandslonein Illinola. altlludeof. 794-7W

acriiunt of B37-38

Sainn, .S. Dak., iirtrainn vrrllit at and near. . . 673 .Salt Illinoia. Hov-ine wella along .. 7iil-783 Sanboni Connly, S Dak . , artcaian wcUain G33-635

artraiao imgatiiin in 488

SauKamon Kiver, Illinoi*, drarription of. . 714-71S

nieanurrmenlji nf 742

Sanxre de Criatn Mountaina, Colorado, de

acription of yri-Wa

Sandfl (dnnvl of nastcm Colurmlo, deacrlptlmof

S79-S80

water of MM

of CM-im

rado, deiicriplion of 977 -J7

ami graTida (upland i of raatem Colorado, deacription of S74-&77

water nf HM-Me

iteodalone of Nerada County, Cal., analyaea

of 99

Scbeellle of )[uld veina of Nevada (;ity audUniaa Valley Cal.,accnmiioa of lit

Sootlaikd. S. Dak., artesian wella at SSS, ATI

Scotland'* volejuiir uecka <'nm|>ared with

thuae of 310-311

Securlly Geyaer mine. Silver CllfT, Coin.,

Security Mining Com iMiny, Silver Oil IT, Olo.,

Work of 449-490

Security mine, Silver CltlT. Colo., analyai* of

kaolin from 4M

S<'illni<'nlar,v rncka of Iho Iml-nirk wrioa, NerailaCily and I iinu Valley diatricta,

('aliforola. ilrai ription of 79-89

of alteration of 1.14-IM

Seririie uf gobl '<|iiartxTeinanf Nevada City

ami Uraaa Valley, CaJ., ortuirraare of lit

dlatrlcta, 52-

nnalyaea of m

Son ell <'oal, Wel Virginia, deacription nf . 496-4VT Scwell formation, WcHt Virginia. dearri|-

tinnof 494-497

Sebaatupol vein, Graoa Valley, Cal., deacrip

tlon of 2Si

Seven'thirty vein, Nevada County, Cal., deacription of 351

Shangbal vein.Uniao Vnlley. Cal . work on. 334 BiUceona rlay. .Silver Clitf and itoalto IlilU.

Colorado, deacription of 3I9-3M

Index

fUlliauui, BwiiamiiL rlud lu. 277

SUTr. BMay of rock* of Cuatar Cooatj,

Colo., for ill

gold prodnctlon of CuiiMr County,

Culo.. Ublr alioirlnic 430

Kllrrr Bur mlDe, SUrer ClilT. Colo., doMirip

tJonof m-tss

by Wliltmaii (.'rnon oa gMlogy of. . . 203-409

Ceopiiphtr ixnittion of 271>-Z72

of of TlT-TtS

geologic reUtlotiahliw of 273

dcsrriptloD* of rwk fonnatloD* of . . . 374-331

of 332-403

history of mlalDK districts of 41S-tl

miurtioii pUntitof 41S-419

produftionof 419-4S0

rliyolltn area of 44s

turin of on ImmUm of HH-itU

raotallic miDerala of 4TO-472

SUver Cliff mill*. Kilrrr Cliff. Colo., cbanir

Ifiranil hinttiry of 4I1MIB

Silver Cliff Mining Coropaoy. work ... 44V Silver Cliff Plataa, Colonulo. drarrip

tion of 305-103

Silver aiff luarry. Silver aiff. Colo., de

ichptioDof 450-4S1

Silver Cliff itmelter. Silver aifl. Colo , rhar

BCtrr and history of 417

SInii, N. Dak., artcaiao well at ac:.6a.6S4

Sinter* of Ueyicr mine. Silver CUff, Colo..

analymmor 4it-4flO

Sioux Cl'y. towa, artesian well at 472, S78

FalU, S. Uak.. artesian well at

Slate Ledge vein. Grass Valley, Cal.. deacriplion

of 211

Sueatb & Clay vein, Nerada City. Cal.. do

MTriptionof 201.102

Soutli Dakota, artesian waters of 003-481. StS-aB4

a<-etlunla M7

Soatli Idabu vein. Uraas Valley, CaJ., drscrlptlon

of. 2H

Soutli Wolf Cri'ek. Gmas Valley, Cal., description of 68-OB

Spanish mine. Nerada City, Cal.. deseriptiuu

of tn

Spect. Jonas, tlrst gold panned lu Nevada

Spencer, S. Dak , arlesiao well at 072

Sphalerite of veins of Nevada City and Gross Valley dlstrleU, California,

occurrence of m

Spbemlitos of Silver Cliff and Rosita Hills.

Colorado, description of 2II-ZM. 40S-40S

Spink Coonty, S. Itak.. artesian wells in. 021-623

artealan Irrigation in US-OOO

Spoon River, Illinois, dnrrlptlon of 714

SpringSeld. S. Ilak..artesisn wells at OK, 653

Spring Hill vein. Uraui Valley. Cal., description of. 2S1-I23

Stanton, T. W.. arknowMgnients to '. 001

Star Mine smelter. Silrer Cliff. Colo., character and history of , 410

Steiger. George, rbenilcal analyaca made

by 130, 140.825,826

Pana

Stephaalle tt quarts Telaa of Nerada City and Grmaa Valley dUtrteta. CalifomU.

oorarrenoe of

StllcM rein. Nerada City. Cal ., work on . . . MO-IOT Uokes. IL K.. cbonilral analyses made by . . H,

41 ML (EL lit 67, sa, IL IS. St Utt .Stoay phosphate of Tenoossee. orcnrrenoe

and character of S37-530

Streator. III., record of arteslsn well boring

Sogar Loaf, Cdo . . rocka o f 373

Sully County, 8. Dak., arlosiaa wells In 631

Sulphide minerals, solubility of I7B

synt heals of jj

Snlphurets of oresof Nevada City and Gtms Valley, Cal., occurrence and character

of IM.lTT

analyses of I2B-HT

Superjacent series the Nevada City and Graaa Valley districts. California, deoriptiooof

K-:n.:-toi

history of 105-111

Swan Creek district. Tennessee, phosphate

deposits of 928-631

Sycamore. 111., Iluwing wella at 7n

Kyeaito of Silver Clifl, Colo , draeriptlon

of jaitjia

aoal.Tsea of ,

T.

Teepeo bntte of eastern Colorado, genre of (PI LXVII,

TeUurinm minerals of qnsrtx veins of Nevada City and Graiu Valley districts. California, occurrence of 117

Temperature in mines of Nevada City and Graas Valley dislricU, Callfomla. range of 170-171

Teoneasee pbospbates, paper by C. W.

Hayeaon 613-519

classification of 519-520

general rrlalionsof S20-52S

black 523-536

wblto 536-549

Terraco sands and gravels of aastom Colorado, deacrlptlon of 577-571

Terrapin Creek (Tennessee) district of phosphate deposits. deMription of 541

Terrible mine. Use, Coin., production of . , . 430

Tertiary deposits of Illinois, scconnt of . . . 801

Tetradymite of quartx reins of Nerada City and Grass Vslley districts, California, occurrence of 117

Tetrahedriteof quarts relna of NevadaClty and Grasa Valley dlstrtila, California, ooenrrenc-eof na

Tezaa vein system. Nerada Coonty, Cal.,

description of 190-191

Thomaa rein. Nerada City, Cal.,

of MS

Thornton, Alex., early mining la Roalta

Hills, by 413

Tlmpasforinatioa. Colorado, description of 560-507 Titanic Iron ore. Hgnre showing intenwth

of pyrite and p,vn'hotlte with ZB

Index.

Page.

Todd CoootT, a. Dak., ulMlan wall In . . aoo-Ml Tmd* Creek (TeoDMaer) dlstiiot of phoptwt

deiMwltm deacription of. M4-&M

Tower City, N. Dak.. artMUa well Ml a6S

tlna area, dncrlptlon of U

Traehfte of Riialta HlUa, Coloiado, occurrence and rharacU-r of 806-307, 340-M3

Trachyte dikoa, Roeiu Hilia, Colorado, deacription of 3aS-3l

Trenton llmeatone under Rock Island, 111.,

and ricinity, acvoiint 836-837

Tripp, 8. Dak., artoian wtilla at and iii'ar. 649.660

aoriptionor 88=1111

Toffs (rliyolltlc) nf Nevada City and tiraaa Vallry dIalrlcU, Catifomla, deacription and analyai* of -W

of Silver Cliir ud the RuaiU HilU, Colorado, ocoum-nc and rbaractr of. . . SHV BM,3S1, 307-399

Tnnwr. H. W.. dtod 82

TumerCounty.&Dak.,arteaisn wells Id. 6S0-SM

TnrtoD, S. Dak., arteaian well at tS2

Twillgtil claim. Onus Valley, Cal.. work on 'JSi

TyiidaU, .S. Dak., arteaian wella at 682.672

analysia of artoaiao water trom well at. 677

account of I'alrozoio rocks of Uock Island. III., by (CB-MB

t'Ddorflow of riven a04l crerka of eaatvm

Colorado, account of 598-001

UndericrouDd water of tlie Arkansas Tal-

Ivy In eastern Culoradu. by

r,. K. Gllbfrt on 5SI-40I

r&ton Hill mine, Qrasa Valley, Cat, loogitndinal

section at 221

Union vein. Nevada County, Cel., deecrlp.

Uonof

rralile-dUbaiMdikea of Ph-asaut Flat, Ne.

vada County, Cel., deacription of lU=fi&

Uralvcin. Nevada Cily. Cal., description of 212-

Cns, K. C, acknowledxmonu to U

Vandarbilt mina. Silver CUff. Colo., daaorlption

of

Vein structuTe of rocka of Nevada City and Grass Valley distrirta. California, description of

Veins of Nevada City and Grass Valley die- '

trict, Callfoniia, description of 164- ,

l71.aiO-220 ,

intersection of IW-ifl?

relation to Keologlcal atmctnie of 1W7-168

generals of IIZ-IM

Teina and Hssares. rhangaa io rooka due to

formation of U.'i-li? I

VennlUon.S. Dak., arlesiaa wells at 6SB

Vermilion County. III., flowioc wells in 779 '

Vermilion River, Illinoia, deacription of., . 7U i

Volcanio flo wa of the Nerada City and Graaa

Valley diatricta, description of 110-111

Volcanic rocks of Silver Cliff and Roaita Uttla, Colorado, rbemical and mineralogical composition of 823-326

Volcanic skies of RcalU HiUa, Oolomdo,

deacription of 284-313

Voy, 0. 1)., California Neooene flora collected

by m

W.

W. T. O. D. Totn. Orasa Valley, Cal.. dew:riptiouof

aao

flgures showing course at 24-250

Wabash River, deacription of tlUnuis tribu-marina

of 717

Wad of Nevada City and Graaa Valley dla-trials

, California, otirurreoce of UQ

Waciconcr, W. W ., ai koowlcdKments to U

WaiU mill, .SitvrrClill, Colo., character and

hiatoryof 417

Wakefield Hill, Colorado, giwlogy of 346-349

Walcolt,C. D.. Calaveras fouils IdentlSed

by

Wall rui'ka of mines of Nevada City and

lirawi Valloy, OaL, analyaea of HI.

149. 1, M. 15.-. m Wall rocka of nituea of .SUver Clllf anil RualU Hills. Colorado. silver

Water of California mines, analyaea of 12L

analysis of deposila uf 122. 123

Water of Geyser mine. SUver CUflT, Colo.,

qiiautitira and obemioal character of. 458-

4S9. 460-4S3 Water of mines of Nevai'a City and Orasa Valley diatricts, Oilorado, character

of

analyses of 121. ITl. 123

Water (artesian) of the Arkaaaas Valley, In eaatem Colorado, and

rhsntc'ter of &80 !M

cheoiical analyaea of 688-S89

kotas, report of N. U. Darton on . . 603-694

rhrmical analyses of 676-678

origin of 679-680

amount of 640-681

Water (artesian) of lUlnoia account of. . . 78&-818 feologle sections showing coorso of . 787,

792. 797, 831 goojtraphic and stratigraphic distribution of

analyses of 827-829

Water (ground) of the Arkanaaa Valley in oaatani Colondo. occumncc and character of 6U6-601

Water (underground) of Arkansas Valley io eastern Colorado, paper by G. K.

Gilbert on &M-601

Water power of Ullnola atrsams, accoant

nf 746-747

Water reaoaroea of Illinoia, paper by Prank

Leveretl on

Water supply of Illinois citiea and villages,

Index.

Pace.

WrathoriiiK of rnok*, provauea of II6-B6

lialit anil clrnrriptiono uf ai7-M5

Wvllii (artmioD) of lUiDoix. account of. . . Ifpologic SMtioiiit rLowIdk ruunie of

water supply of 787. IK. T7. 31

f;graphic ilitribatioD of i

tralisrapliifdUtribationof mri-ms

drptliof m-tm

tabulated dat* SlM-IM

aualyHea of watf rn of 837-828

of T72-7ffi

Veil driUingi, Darenimrt, Iowa, rrcorda

of IM2-WS

WcU'Water aupply, IlllnoU cUira and vil

lagM 7M-7M

Illiuoia rural dUtrlrta

'Wnt Harmony drift mine. Xevadn County,

Cal., flguTM of aertioDa at Kio

Veat VirginiA, gmlogyof MMtion alongNew

and Kanawha rivera In

WeatiMirt B. Dak.. artMlan well at 618

analysis ot artcalan water fWim well at. 877 Wet Mountains, Colorado. . . STl, SZi Wi't Uuontain Valley, Colorado, demrlption

of. 2Bts2Zl

White, T. A., Bcadlo County. Dak., arteaiao

Irrigation by 083,684

White Lake, S. Dak., armenian wrils at. . (3. 071 Whit phoapbatrit of Teuumaw, charaotor

and iicrurrenoe of

Carbunlferou* ruck* aaaucialed with. S3S-&37

chemical rompiMiltian of. &3tf

utiUaation uf S4A-A4I>

Whlliiey.Milttin. citml 725

Paite,

Whitney, W. D., cited Ufl

Wide Wet vriu, Nevada County, Cal., de-

WiKbani vein, Nevada City, Cal.. dcarrip.

liun of an-j-ans

Willow Valley. Nevada County, Cal., gold

quart! vein of IM, lift- 181

WlaiblMlon. N . Dak . artesian well at lies

WlMunnin mine. Grass Valley. Cal.. flicure

loK ioDgit udinal station on 2ti

WlaouuHui Illiuoia vein. Grass Valley. Cal.,

drMTiption of 2*4

WoUantouite of Nevada City and Graaa Valley dljitrlrla, Cnlifomia, occurrencnof 12D

Wolaey.H.Dak.. artesian well at <BJ,2S.im

WoodTille Vein. ye\ aila County, Cal.. diagram of 1B8

Wooiuujrket. 8. Duk.. artesian welU at. . . 633. 634 analysia of artesian water fruni well at. 677

Yankton. S. Dak., artesian wells at and

near e&5-A57

analyses of artesian water from well at. 677 Vanktou County, S. Dak., arteaian wella

In aM-e57

artesian irrigation in 680

Tankton Indian Agency, S. Dak., arteaian

woUat 64.6i7

Tellow Diamond rUtm. Nevada City, Cal.,

deacrlpUon of — 21fi

Z

ZiiK' blende of quarts reins of Nevada City and (irass Valley diatricta, California, occurrence of Ut

To avoid fine. iUs book should be retinncd oa or before Idx date but (tamped bdow

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563.41 .L745 C.2 Th* gotd-quartz win* ol Ncvad

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