Prospecting for gold and silver [microform]

Lakes, Arthur, b. 1844 · 1895 · Historical

Includes index

Public-domain full text preserved in the Mountain Man Mining Library. Original source: archive.org.

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Prospecting

For

Gold And Silver.

By

ARTHUR LaKEs,

Late Professor of Geology at the State School of Mines, Golden City, Colorado,

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Author of ''GrOLOGY OF COLORADO AND WESTERN ORE DEPOSITS, '*GEOLOGY OF COLORADO COAL Deposits," Etc.

Scranton, Pa. The Colliery Engineer Co —

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Entered according to the Act of Congress in the Year 1895, By THE CoLutery ENGINEER Co.,

In the Office of the Librarian of Congress, at Washington

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Preface.

In preparing this little work the author has felt the difficulty which arises in a theoretical dissertation on so eminently practical a subject as prospecting. It seems like giving rules and prescriptions for hunting or fishing or any other natural or practical pursuit. Though theory and practice are not at variance when happily combined, yet. either without the other proves very unsatisfactory. Thus. the reader of this book, should he start out armed only with its theory, will find himself for some time pretty much 'at sea" when he comes to actual practice in the field. As, however, he gradually obtains some practical experience, he may find this little work of use to him. So, also, the seasoned prospector, who has hitherto trusted to luck, keenness of observation, intuition and experience, may find himself in the future much better equipped by acquiring a little of the theory.

Whilst we have endeavored to give the prospector all assistance in our power, as to the best means of educating himself, describing his outfit, etc. we have devoted special attention to the description of such geological and other phenomena as he is likely to meet with in connection with his work, so that he may have an intelligent idea of them when he encounters them.

We have selected just as much material as we think would be most interesting and useful to him, saving him the time and trouble of wading through heavy tomes and laboriously picking out from a vast amount of, for his purpose, superfluous matter, that which he will most require.

The work is intended to be a popular one, addressed to the average student, prospector and miner and to the generai public. The illustrations are largely drawn by the author from Colorado mines and Rocky Mountain subjects which are most familiar to him.

ARTHUR LAKES, State School of Mines, Golcen City, Colorado. JANUARY 1, 1895.

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Chapter I,

Contents.

On Prospecting—Preparation and Outfit for Work. --- The Prospector's Historical Geology The Prospector's Paleontology or Study of Fossils. - - - - The Prospector's Lithology or Study of Rocks. The Prospector's Mineralogy Ore Deposits—Theories Regarding the Origin of Ore

Deposits 2-20 eee eee eee e en eeee-- Various Forms of Ore Deposits... oaek keemenas Relation of Veins to Eruptive Forces Gold Placers. 6. .cc cine. cancdoceccoussnnasededonses Deep Leads 2 20 -- ene eee eee en nen anes Mining Regions—Showing Examples 6 Ore Deposits. - Ore Deposits in Sedimentary Rocks Examining and Sampling Mining Properties, Prospects

OF MINGE ee beccc cee sccdewbsacctesse an eensergeasies Salting Mines... 2... 26... --.s0 news n none cesssscoces Prospectors' Tools, and How to Sharpen and Temper

TRON ois ode c wales coke wea ¥eeesies eae ca dean ces tawe Some Elements of Mining Law Relating to Prospecting -

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Prospecting For Gold And Sulver.

Chapter I.

On Prospecting—Preparation And Outfit For Work.

The regular prospector, as a rule, has at some time of his checquered career had some actual experience in the mines themselves, from which he has learned by observation, the appearance of different ores, their different values, how the veins appear on the surface, how to open a vein, and the uses of pick, shovel, and blasting powder. Ina word he is a miner, who has become too restless to stick to steady work, and so follows the more uncertain and precarious livelihood of seeking for new and undiscovered veins, many of which even in an old mining district may yet be discovered covered up by brush or debris, whilst a new district offers a most enticing field. These mineral veins or ledges, may make him in a moment a comparatively rich man, and if he finds them, they will cost him nothing, only a simple com-

liance with the inexpensive regulations of the law. So the life of a prospector offers many attractions to one who is restless and loves to roam and loves to find something new and is not afraid of considerable hardship. To save a vast amount of time and labor, he should acquire knowledge. Thus, for instance, if he were prospecting for coal he would be Sees his time in hunting for it in granite, or if he was hunting tor the precious metals, he would lose time in looking for them among the unaltered sedimentary strata of the prairie. This is merely for example, but an infinite variety of knowledge is necessary for him in his vocation, besides even that of the simpler elements of geology, such as the knowledge of different kinds of minerals, and their value, the kind of places and peculiar rocks they are associated with, their appearance on the surface, etc., etc.

together with some knowledge of assaying or blowpiping or panning.

In a newly discovered camp, men will rush in for a few weeks, work a little in the different mines, sufficient to give them an idea of the kind of ores and rocks and other circumstances in the locality, and then will strike out on their own account and prospect around the camp for new veins or extensions of those already discovered, An extension, by the way, of a very rich discovered lode is not always to be relied on, Nature seems often to concentrate her riches at one point, and leave the extension barren, as in the case of the Comstock of Nevada. But little wealth has been found outside of the great lode and mine itself.

The best education is in the mines themselves, so a novice on arriving at a mining region had better spend as much time as possible in practical work, in, and around the various mines, before he launches out prospecting. A prospector can ica carry about much assaying or other apparatus with him for determining the character or value of ores he may find, and hence it is well for him to accustom himself to these ores in the mines themselves. Also he should acquaint himself with the peculiar ores of each particular district, before he attempts to prospect in its vicinity, for an ore such as coarse grained galena, in one district may be generally rich, whilst in another it is remarkably poor in silver.

The best previous education for a prospector would be a course at school of mines, where he will learn the elements of geology, mineralogy, assaying, etc. And next to that, practical work in the mines themselves, and lastly the prospecting field. A little knowledge of blowpiping may also ne him, which he may acquire at his school.

Having left his school, he should learn the practical use of the pick, drill, and, blasting powder. By working around a concentrator he will learn the difference between ore and gangue rock; and "picking" or "sorting" ores, will teach him at sight the values of ores. The prospector should know how to open his vein or ledge, when he finds it, with pick, shovel, and blasting apparatus. A little carpentry will teach him how to make a handwinch, and a few lessons in blacksmithing, will teach him how to sharpen and temper his tools, for there will probably be no blacksmith's shop or carpenter's either, within miles of where he may go. Other prospectors will teach him how to use his pan or iron spoon for testing ores, and various other dodges and

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make-shifts. An important point is to learn how to average approximately the quantity of ore in, and value of, a ledge when he has found one. Valuable ore on a ledge lies in pockets, strings, bunches, irregularly distributed through the quartz or other material of the vein; he should learn to tell at sight the relative proportion of ore and ganguc. He would do well to study the result of working ores in a mill or furnace, such as trying to estimate the yield of bullion of the ores which are mined, hee them in weekly or monthly lots. With some such preliminary knowledge he is ready for the field.

His Outfit,

The following list of necessaries by Mr, A. Balch in his "Treatise on Mining" is as full as can be given by any one,

and is more than the average prospector generally needs,

A Prospector And His Outfit.

"First. Two pairs of heavy blankets weighing about 8 pounds each.

Second. A buffalo robe or a blanket lined poncho.

Third. Suit of strong gray wooden clothes, pair of brown jean trousers, a change of wooden underclcthing, woolen socks, pair of .eavy boots, soft felt hat, three or four large

colored handkerchiefs, a pair of buckskin gauntlets, toilet articles, etc. All should go into a strong canvas bag. [i Fourth. A breech loading rifle or shot gun and a revolver. Around his waist a strong sash to carry his holster and s knife, ina sheath. His ammunition, if his revolver is large bore, may conveniently fit both his rifle and revolver. Pipe and tobacco. Fifth, A sure footed native or mountain pony. A $ Mexican saddle with its saddle horn, straps, etc., to tie on various things, such as his pack, bags, water canteen, ctc. The left stirrup may be fitted with a leather tube, in which the rifle barrel may be placed. A strap around the saddle horn will secure the gun stock. The long lariat or stake

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A Prospector''S Tools.

1, 2. Picks. 8. Pan. 3. Long handled Shovel. g. Horn Spoon, j 4, 5. Drills. 10, Iron Spoon, 6. Heavy Hammer. 11. Fuse.

7. Blasting Powder.

rope for tethering his horse should be coiled up and tied by a strap to the saddle horn.

Sixth. For prospecting, a 'poll' pick and prospecting pan made of iron ora horn spoon should be carried. The pan is also useful besides for washing out sand, as a dish or bathing vessel. A large iron spoon for melting certain metals is likewise to be carried, and in some cases a small portable Battersea assaying furnace.

Seventh, frying pan 8 inches diameter of wrought iron, a coffee pot, tin cup, spoon, and fork, and matches in tin box, pocket compass, a spy glass, or pair of field glasses,

Eighth. Provisions, bacon, flour, beans, coffee, or tea, pepper, salt, and box of yeast powder, all packed in strong bags, to go into a canvas sack. A few lessons in the kitchen on cooking will be advantageous before starting.

Ninth. Packing the bronco. Place a folded blanket on the horse's back, on this lay the saddle. The saddle bay's contain small things. The bags with provisions are placed behind the cantle of the saddle; on top of this the bag of clothing. The pick goes on top tied by a thong. Coffee pot, and frying pan are lashed on the bags."

Sometimes a prospector takes a horse to ride on and another as a pack animal, or a donkey only. For grass and water for his horse, he must trust to the country. He will fix his temporary camp in some suitable location, where these are to be found, and thence, as from headquarters, prospect daily the adjacent country returning nightly, it may be, to his camp.

Brief Sketch Of Prospecting.

We may divide the- prospecting for the precious metals into two general classes: hunting for gold in gold placers; hunting for gold and silver bearing ledges or veins or deposits.

"Placers" are places where gold having been torn from the ledges and rocks by denudation, by water and ice, is swept down by these agencies till it finally finds a resting place. Gold being heavier than quartz or country rock, sinks to the bottom first. If the stream is violent, it will carry the gold on, if fine, till it comes to an eddy or pooi, where the waters are more quiet, and there it will sink. The water carries the clay and lighter stones still further on. In this way millions of tons of rocks containing more or less gold disseminated through them may have been reduced, and the gold set free, or the gold may have been derived from a few individual gold bearing ledges or veins.

The prospector takes his pick, shovel and pan, and his horn spoon, and finds perhaps an old dry river bed where the water has ages ago receded. At some point the sides of this old river course widen out suddenly, forming' a basin. "Here," says the prospector, "there must have been an eddy," and he prospects it accordingly; at another point he finds a place where the water must have run over a rock, and made a waterfall; at the bottom he digs again,

He loosens the soil with his pick, and shovels it out; ata

certain depth, which may be from 5 to 20 feet or more, he strikes "bed rock," which may be granite, shale, sandstone, or some other rock. Here he looks for nuggets, and with his knife digs into all the little crevices of the rock to hunt for them and for scales and wires of gold.

Panning Gold At Cripple Creek, Colorado,

Also whilst sinking his shaft, he pans the gravel carefully at various depths, especially where there are streaks cf clay or "black sand." The latter are grains or little pebbles of magnetic iron ore,acommon accompaniment of gold, altered

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relics of the iron pyrites in which the gold was originally contained.

He fills his pan half full of water, throws into it a shovelfull of dirt, first picking out the pebbles, stirs the mass with his fingers tilt the water is fully charged with the clay and gradually winnows out all the clay. Filling the pan again with water, he gives it a peculiar circular motion and each little wave of sand passes off till the whole is winnowed off, and at last he sees specks of gold shining free in the bottom of the pan. Then it is not difficult to estimate approximately the amount of gold to the bushel or cubic

Finding The Float.

foot of earth of the placer, and thus to estimate the approximate value of the placer. He then locates or stakes out his placer claim according to the regulations of the U.S. Government, which, by a single individual cannot exceed twenty acres.

The second class of prospectors are those who try to discover ore deposits, ledges or veins, "in place," that is, in the hard rocks of the hills.

The prospector's first effort is to fine "float." A vein outcropping on the surface, becomes oxidized and crumbles by action of the atmosphe.e, rain, etc.; pieces break off and fall down hill. Some of this float is barren quartz or country

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rock, others may be mineralized. Commonly "float" is a rusty, spongy mass of rock, showing besides iron often some copper stains, and in it there may be grains of galena,

yrite or some other ore, He tries to trace this " float" to its home in the ledge whence it came. Of one thing he is certain, the " float' must have rolled down and not wf hill. If the "float" is fairly scattered over the lower zone of the hill, and no " float" is found above that zone, on the top of that zone he will hunt for his ledge. If the " float"' is all over the hill he assumes the ledge is on the top.

If he finds his " float" at the mouth of a canyon or water course, he walks up that water course, noticing not only the " float,' and its diminishing or increase, but also any peculiar rocky pebbles, such as a peculiar porphyry, perhaps, which he may by chance recognize again further up in place, and give him a hint as to whence the stream derived most of its material of pebbles. He notices if the " float," fragments increase as he proceeds, and whether they suddenly cease at a certain point; at that point he hunts for the ledge on either side of the canyon, and breaks off any pieces that may look likely.

Having found the ledge and traced its croppings, he tries to find out its approximate value. This he does by breaking off at intervals along it likely looking fragments of the rock, grinding them up to about the size of peas. He mixes these well, and takes a half of them, reGnelng this to fine powder, and again halving it, till of the whole ledge he can carry away an averaged sample of afew ounces. He may wash this in his pan to see if there is any free gold in it; other ores he will recognize at sight. These samples he will have assayed and the returns will show the approximate value. He measures the length and thickness of the vein, and examines the wall enclosing it.

He then proceeds to locate or stake it out by measuring off a parallelogram 1,500 by 600 feet. At the corners of this, he places piles of stones, and in one or more of them places a stake of wood on which he writes his name, a description of his claim and the date. At the nearest recorder's office he files a copy of this document. He must do a certain amount of improvement work on this annually, such as digging a ten foot hole or putting up a cabin or some work equivalent to the value of $100, so as to hold it. He may also claim a mill site on non-mineral land adjacent not exrida 5acres. Now the property is his to doas he likes with it.

The Geological Training Of A Prosfector,

One of the first things for a prospector for gold and silver to acquaint himself with, is the elements of geology. He can read this up theoretically in many excellent treatises and manuals, such as LeConte, Dana, and Shalers' Manuals, and Geikies' Hand-Book of Field Geology, etc., and become learned in the names of eras and epochs, and the jargon of scientific names of fossils and minerals, and varieties of rocks; but let him not imagine at the end oi this process. that he "mows geology."

Geology can no more be learned by means of a book, without field' work and the actual personal contact with nature and rocks, than chemistry or assaying can be acquired without ever using a test tube or a cupel. The student may, perhaps, be unfavorably situated for this practical field work. There may be no mountains or upheavals of strata, or deep natural ravines within available distance to study. He is located, perhaps, on the great, monotonous, flat prairie. Very well, then let him study what lies nearest him. This same flat, monotonous prairie has an interesting and wonderful history Let him read up what he can find about this in his books, then go out and examine what he can of the few feet of horizontal strata exposed in some shallow water-course or dry ravine; examine minutely, both with eyes and microscope, the minerals composing these strata. Let him classify and collect and note the different kinds of pebbles .cattered over the surface, or in the bed of a brook. Let him speculate as to the cause of the undulations of the surface, the deposition and peculiar character of the clays forming the soil. Let him study thoroughly the geology of his native village, his immediate surroundings, . The knowledge and practical habit of observation so acquired, will lead later to more extensive studies in wider fields. A student may be shut up in a big city; let him study the paving stones of the streets and visit the stone yards of the masons. It will pay him better to take a trip to some distant mountain region, than to buy another expensive book on geology after he has mastered the first bare elements, Nothing like field work, eye practice, and hammer practice. The student should endeavor, whenever he ry can, to verify by actual vision and personal experience whatever he reads in his books. When traveling, let him always carry a geological hammer with him, and at any

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station the train may stop for a few moments, step out anc try to get a specimen of the country rock; at the same time let him study all he can of the geology of the country he is passing through from the windows of the train, aided perhaps by a geological map. The genuine prospector is always looking about him, is everlastingly cracking stones, has always his eye wide open for "something kind o' curious."

If he is near some mountain region, where, as in Colorado, the whole strata of the earth's crust is upheaved and exposed, along the mountain flanks, in the depths of the canyons, or on the summits of the peaks, after studying his manual, let the student get, if he can, some published

eological report on such a country, such as those of the v. S. Geological Survey, abounding in illustrations and geological sections. Let him take this book in hand and go

to the very place described and pictured as a geological

section, and with his hammer study each member of the section ciosely. This will make him familiar with the different geological periods, formations, rocks, minerals and fossils, as they actually appear in nature rather than as his 2..ag¢nation has supposed them to be from his study of the text books: book geology and field geology are not always in perfect harmony.

Having studied and learned one local section well, such as that cut by a stream along the foothills of a mountain range, let him repeat the course at the other and more distant points. He will find at each locality, though the main features are the same, there is always an interesting variety, such as new fossils, peculiar minerals, changes of dip, faults, or other structural peculiarities.

Along the flanks of a mountain range, a prospective prosnector cannot study too many of these geological sections. Having become familiar with these foothill sections, he is prepared to plunge into the heart of the range itself. At first, and for long distances perhaps, he will encounter only granitic rocks forming the axis and core of the range. These are well worthy of study and full of variety. Later the canyon may open into some mountain valley or park, where the strata he studied on the foothills or prairie border are again repeated and he finds himself again at home. Seizing upon some well defined and familiar representative of a geological horizon, from this as a standpoint, he soon reads off the succession of the rest. Here, however, the. appearance and texture of the rocks

will probably be different to what they were in the foothills. Heat has so changed or metamorphosed the sandstones and Hil shales, that they are scarcely recognizable as the same rocks Hi as those of the foothills. Yet even here a highly silicified i fossil shell, or a leaf impression on shales, or sandstones Hi changed into slates or quartzite, will give the prospector i his clue and his desired and definite geological horizon, and he will have little difficulty in again arranging and grouping Ht correctly the rocky series. But a prospector has a " practi- Ht cal end" in view. He is "after the precious metal," gold tM and silver, not after "pure science" or "fossils or sich '; ih what practical use in there, he may ask, in this same careful it study of geological sections, where probably there is nota i speck of gold or silver? Simply that minerals and metals of economic value, such as gold and silver are more fre- i quently found in the rocks of certain geological periods than in others. Locally this is especially true. For inti stance, nearly all the silver-lead deposits of Colorado are found in a certain bed of limestone not over 200 feet thick, "i to be found only in one geological period out of many a others, viz.: the lower division of the Carboniferous. It i would naturally then be advisable for a Colorado prospector Th to be able surely to identify this limestone, as well as the geological horizon in which it occurs, among the various i other limestones of various other periods and ages in the mountains.

Again, gold is mainly confined to crystalline rocks of t) Archean age or to porphyries associated with these. A H

prospector should be familiar with these rocks and their varieties, Gold is also found in the placers derived largely from the breaking up of these rocks; the ability to distinguish the different pebbles may lead to the source whence the gold was derived. Familiarity with rocks of all kinds is a necessary prospector's education in itself.

Geological Sections Of Colorado,

In illustration of what we have said, let us take the two engraved generalized sections showing all we know of the crust of the earth as exposed in Colorado. Plates I and II.

Plate I is a vertical section of an ideal cliff, showing all the members of the various periods in a stupendous cliff resting on fundamental Archzan granite at the bottom of a canyon. Plate II represents the same rocks and succession of strata displayed in upturned "hog backs" along the

flanks of the mountains and foothills on the border of mountain and prairie. Both of these are ideal sections "generalized" or "made up of actual partial typical sections found in different localities in Colorado, the vertical

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can be seen by the traveler from the windows as he glides through in the railway car, and the inquiring prospector or geologist can examine and study this vast section leisurely

on his mule or on foot, without doing any climbing and on

a good road. Smaller partial sections can be similarly

studied along many of the streams issuing from the Rocky Mountains among the foothills of Colorado. Such, for

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flanks of the mountains and foothills on the border of mountain and prairie. Both of these are ideal sections "generalized" or "made up" of actual partial typical sections found in different localities in Colorado, the vertical

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will probably be different to what they were in the foothills. Heat has so changed or metamorphosed the sandstones and shales, that they are scarcely recognizable as the same rocks

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In illustration of what we have said, let us take the two engraved generalized sections showing all we know of the crust of the earth as exposed in Colorado. Plates I and II.

Plate I is a vertical section of an ideal cliff, showing all the members of the various periods in a stupendous cliff resting on fundamental Archzan granite at the bottom of a canyon, Plate II represents the same rocks and succession of strata displayed in upturned "hog backs" along the

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flanks of the mountains and foothills ou the border of . mountain and prairie, Both of these are ideal sections "generalized" or "made up" of actual partial typical sections found in different localities in Colorado, the vertical one in detached and sometimes widely separated districts in the heart of the mountains; the other at similarly distinct and different localities along the banks of the various rivers issuing from these canyons in the mountains, cutting their way through the upturned strata of the flanking foothills and debouching on the prairie.

It is very rare to find at one locality anywhere in the world, acomplete section of the earth's crust exposed, The nearest approach to this in Colorado, is the remarkable section between Colorado Springs and Manitou, which shows along the wagon road the succession of strata from Archean to Quaternary,

One of the most remarkable ver/ica/ sections in the world, is in the grand canyon of the Colorado River, where the stupendous cliffs show in one face, a thickness of some 6,000 to 7,000 feet of strata, representing several geological

eriods, but by no means a complete section of all that is Snow of the earth's crust.

To show how difficult and rare it is to to get a complete section of a//the periods in the earth's crust, we may state that sometimes the rocks of a single geological period are from 10,000 to 20,000 feet thick. A canyon might thus be cut to a depth of 5,000 feet, and yet be in only part of a single earth-period.

By far the most extensive and available sections are, like those represented in the engraving, along the courses of streams on the flanks of a mountain range. It would bea formidable task to scale a cliff 5,000 feet high and examine minutely, in ascending, each of its geological divisions; whilst, on the other hand in the foothill regions, a prospector may walk over and mark and study as much as 10,000 to 40,000 feet of strata along the banks of a river in a single afternoon. In the Weber Canyon in Utah, as much as 40,000 - feet of strata, composing the flanks of the Wahsatch Range, can be seen by the traveler from the windows as he glides

through in the railway car, and the inquiring prospector or geologist can examine and study this vast section leisurely on his mule or on foot, without doing any climbing and on a good road. Smaller partial sections can be similarly studied along many of the streams issuing from the Rocky Mountains among the foothills of Colorado. Such, for

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example, as at Boulder Creek, Clear Creek, Bear Creek, the Platte River, and, most complete of all, the one along Fountain Creek, near Colorado Springs, which we 'have already mentioned. Similar sections can be found in most mountain regions, such as the Adirondacks in the East, and the Sierra Nevada and Coast Range in the West of America. We emphasize again, that the close study of these is the best preliminary step we know of ina, rospector's geological education. Let us now examine our ideal generalized Colorado section which we will suppose to be all exposed along the banks or canyon of a single river. We will start from the Archean granite in the canyon, thus giving usa sure and known and lowest possible geological horizon to begin with.

The Archaan.

This Archzan we find to be composed towards its core, of solid, shapeless (amorphous) crystalline granite, which seems to have been fused out of all shape by water and fire, or aqueo-igneous fusion. With this, but more characteristic of the upper and outer edge of the Archean, the granite assumes a more Stratified and bedded character, which we designate as "gneiss" and interbedded with it at intervals are distinctly laminated or finely leafed strata, called schist ; all these varieties are composed of the same minerals in different arrangement and quantity, viz., mica, quartz, hornblende, and feldspar. As these rocks are semi-igneous or metamorphic, we find no fossils in them. Traversing all these Archzan rocks and cutting them at ail sorts of angles, we may notice some eruptive dykes of porphyry, which were once certainly molten and have ascended in that state through fissures opened in the rocks from depths and sources unknown. As we approach the edge ot the granite we may even see some of these molten rocks, insinuating once fiery tongues among the weak places and bedding planes of the overlying sedimentary strata, as represented in the diagram, where one dyke is shown to have sent out so thick an intrusive sheet of porphyry, (see Plate II), between the overlying limestones, hat where subsequent erosion took place, this thick sheet, by its superior hardness, was left to form the highest cap of the mountain, as on many of our prominent mountain peaks such as Mt. Lincoln and others in South Park.

Besides these rocks, the prospector will observe numbers of quartz and pink feldspar veins of all sizes, some mere

:

streaks and occupying incipient fissures or weak places (veins of segregation), others peel th large well defined fissures or jointing planes (so called true fissure veins). Some of these may or may not carry metal, gold or silver, lead or copper, at any rate he will pay them especial attention particularly if any of them look at all decomposed or rusty, or are in close proximity to an eruptive porphyry dyke. ; THE CAMBRIAN.

Now the prospector emerges from the Archean granite and finds the first true sedimentary, water-formed rocks lying where the ancient seas placed them, on the eroded upturned edges of the granitic series.

If this section should be near the plains or foothills, this first sedimentary rock will be a sandstone, pure and simple, or a conglomerate of little pebbles, but in the parks and center of the mountains where these ancient strata are most conspicuous, the first rock lying on the granite is a hard, white, semi-crystalline quartzite or metamorphosed sandstone. He may possibly find some obscure signs of ancient fossil shells in this series, which is called the Cambrian now, though formerly it was held to be only a lowe division of the Silurian. In Colorado these Cambrian rocks rarely exceed 200 or 300 feet in thickness, but in other regions they are often very much thicker. In this series the prospector may look for precious ore, more especially gold. He will carefully look also for intrusions of eruptive porphyry in this series, as at the junction of this with the quartzite, ore is most likely to be found. He will also observe any rusty signs filling cracks, as good indications of gold bearing ore. Silver also may be found associated with lead or zinc.

Silurian,

Walking along, he next comes to some 200 or 300 feet of drab-yellowish or light gray thin bedded limestone of a dolomitic character, characterized by numbers of little white flints or (rarely in Colorado) by some fossil shells, which, by reference to the engravings in his manual, he finds to be Silurian, and so recognizes the series. Here he may find indications of lead, silver or other ores, but not much gold as a rule.

Carboniferous.

The next series of this should, according to the textbooks, be the Devonian, characterized by fossil fishes and

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"Old Red" sandstones; but the rocks of this epoch for some reason are missing in Cviorado, Instead of this, resting on the Silurian, he finds a thick bed of heavy bedded, massive, '' blue-grey " limestone, characterized by black flints, and at rare intervals by fossil shells and corals, which again, by reference to his book, he finds to be characteristic of the Lower Carboniferous. This limestone when traversed by sheets of erupiive porphyry, has yielded at Leadville and at Aspen and New Mexico and Arizona, some of the largest s!lever-lead deposits in the West. In fact, throughout the West it may be considered as the main silver-lead horizon. This limestone is generally between 200 and 300 feet in thickness and readily recognized by its position relative to the Silurian below it, and the inassiveness of the strata, and their dark grey color. It is commonly called the "Blue Limestone " in Colorado,

Middle Carboniferous.

Next on this, is a bed of dark black shales in which thin seams are sometirnes found, and fossil plants, like those in the coal strata of Peunsylvania, sufficient to show that it, too, belongs to the Carboniferous, This is followed by some 2,000 or more feet of "grits," rough, hard, gritty sandstones, partially changing into quartzite, akin to the mill-stone grits" of the Eastern States. A few limestones occur in this thick Middle Carboniferous series, which locally, when capped by porphyry, produce silver-lead deposits ; but generally speaking, the "grits" are unproductive in Colorado.

The Upper Carboniferous consists of beds of gypsiferous shale and heavy, brownish red conglomerate sandstones.

Triassic '' Red-Beds,"'

From these we pass into a series of heavy bedded, coarse conglomerate sandstones of a brick-red color, commonly known as the " Red Beds" in Colorado ; little indications of ore are to be expected in this series. The prevailing redness of the series makes it an easily recognized geological horizon in Colorado and elsewhere. The thickness in Colorado varies from 1,u00 to 2,000 feet.

JURASSIC, Next, the prospector comes to a softer and more variegated series, consisting largely of pink, green, red, or

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maroon marls and clays, with some thin limestones and red sandstones. This is the Jurassic series in which some remarkable lizard remains, called Dinosaurs, have been found, proving the correctness of its Jurassic name. This is not a likely mineral horizon, generally speaking, in Colorado.

Cretaceous.

These softer beds are capped bya hard massive sandstone about 200 feet thick, forming by reason of its superior hardness a prominent hog back in the prairie or foothill region. Fossil remains of leaves show it to be a land and fresh-water group, which is called the Dak. 'th group.

This group in Colorado forms the base of the great Cretaceous system; lying on it, is an enormous thickness of drab shales with a few limestones characterized by fossil sea shells, showing the group to be the marine Cretaceous, likewise a poor prospecting ground. Towards the upper portion, these shales pass gradually into heavy bedded sandstones containing several seams of coal, and many impressions of tropical foliage. This is the Laramie group of the Cretaceous, evidently of fresh water origin, and noted as the main coal producing horizon in Colorado and the West.

Tertiary,

On this, at a somewhat gentler angle even to horizontality, rest thick beds of shale and clay and conglomerate, composed of volcanic detritus and pebbles, showing that at the time these Tertiary beds were being laid down by large fresh water lakes and marshes surrounded by tropical foliage, volcanic eruptions on a grand scale repeatedly occurred, Hence it is that many of the Tertiary beds are preserved from erosion by being capped with volcanic rocks, such as basalt, andesite, or rhyolite,as at the Table Mountains at Golden, on the Divide near Colorado Springs, and elsewhere in Colorado. One of these lava capped '""mesas"' is represented in the section, Plate II. Fossil leaves and coal seams are found in this period.

Quaternary.

Lastly, strewn indiscriminately over all the formations is the "Quaternary drift'? composed of loose pebbles, and sands, and clays, the material derived from rocks of all the periods through the agency of glaciers and streams,

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Here the prospector will pan for his gold placer, and in his search may possibly come across the teeth or tusks of the great Mammoth or fossil elephant, together with the first indications of the presence of primitive man. The pebbles by their variety will form a fertile subject of study to determine to what class of rocks they belong.

This ends the prospector's first preliminary lesson in Colorado; but taking this section as a type, he may to his great advantage, similarly study other sections far remote from Colorado.

In Colorado, if he knows this section by heart, he has the key to nearly all our mountain structure, and will be at home wherever he goes. He will be struck, too, to see to how small a portion of this great section the precious metals are more or less confined, principally to the Archean and Paleozoic rocks.

Chapter Ii. The Prospector'S Historical Geology.

In our last chapter we gave some hints to the prospector how to commence his geological studies, and gave him an example of a geological section of the foothills and mountains of Colorado, and how to study it in detail practically. Having completed this study, if a thoughtful man, he will like to know more of the natural history of all this section of the earth's crust : what is the natural history of the Archzan, the Cambrian, Silurian, etc.. why do some of these strata contain sea shells, 2nd others land plants, why are some evidently of marine, and others of fresh water origin, and particularly why are some especially metalliferous, and others not so much so. We propose, therefore, in this chapter to give him a brief sketch of the earth's history as exemplified in the section, Plates I. and II.

Hypothetical Origin Of The Earth.

The world was not "spoken into existence ready made' in the state we now find it. It has attained this condition through a multitude of gra' ial changes and revolutions which have taken millions years to accomplish. The

j

remote history of the earth's origin is a matter of hypothesis and speculation. There are reasons for supposing that at one time its elements were in a gaseous condition, and that this planet was an incandescent luminous cloud revolving through space, gradually consolidating into a molten ball surrounded still by an atmosphere of gases, a condition perhaps not very unlike that of the sun, whose interior by some is supposed to be passing into the molten state, while its exterior consists of various incandescent gases arranged more or less according to their specific gravities. The spectroscope has detected the elements of some of our earth metals and minerals in the sun in state of vapor, The ultimate source of the precious meic.s is again a matter of speculation like the nebular hypothesis we have alluded to, by which the earth, as we have said, is supposed to have arrived at its present condition as the result from the gradual cooling of an incandescent mass, and as the specific gravity of the crust is much less than that of the whole mass of the earth, it has been inferred that the heavy metals must be in much larger proportion in the interior of the earth, than in the rocky crust, though this greater interior spesiy gravity might be also accounted for by the rocks of the interior being much more tightly packed by enormous pressure than those near the surface. Volcanic emanations and hot springs contain metallic minerals, so also do the waters of the ocean. But we know not from what depth the former came, nor from what source the latter de..ved them. As circulating waters take up and throw down their metallic contents under varying conditions, the same material may have been deposited more than once, and in more than one form since it reached the rocky crust.

Upon the cooling of the ball a crust formed like that on molten iron, crumpled and corrugated by contraction, due to cooling, into an uneven surface, with comparatively slight elevations and depressions, and doubtless broken through here and there by great fissures and volcanic craters, through which the molten flood beneath poured out in volumes, adding to the thickness of the congealing crust.

Upon such a surface the gaseous atmosphere, gradually cooling and condensing, descended as hot chemical rain, and filled the troughs of the crumpled surface with a hot, chemical, steamy ocean. Whatever land of primitive lava rose above this ocean was battered by the waves, reduced to sediment, and deposited as the first sedimentary strata in the bed of that primeval ocean, the eruptions from below

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the thin crust doubtless contributing largely to the same material. ARCHAAN AGE,

Thus, perhaps, were formed the first stratified rocks of the world, which we have an opportunity of actually seeing and studying, viz.: the granitic series, with its varieties of gneiss, schist, syenite, etc., and as this is the beginning age so far as we know, we call it the Archzan, the Greek for beginning. It would seem probable, however, that these granitic rocks forming the axes of our mountains, may not, at least in part, have been the very first rocks of the crust, for we observe some of them such as the gneisses and schists to be stratified, and to show elements in them seemingly derived from other and still older rocks, which latter may or may not have belonged to the original cooling crust. Some geologists claim that the Archean is the first cooled crust and attribute it toa molten origin. This may be true for the seemingly fused massive amorphous granites (though these may be but the result of aqueo-igneous fusion of sediment or extreme metamorphic action), but scarcely for the stratified gneisses and schists, though it is to be noted that a sort of stratified or schistose structure is sometimes observed in truly igneous rocks and may be induced by peculiar arrangement of minerals, pressure and cleavage, instead of water lamination.

The subject is a difficult one and too abstruse for the limits of this work.

In the scale of geological periods in the text-books. we sometim es find this great Archean divided into two or more groups such as the Laurentian, Huronian and of late the Algonkian. The Laurentian is the oldest and may be called the Archean proper, whilst Huronian and Algonkian may be grouped generally as Pre-Cambrian, or series of rocks laid down after the Laurentian and before the Cambrian. All the rocks are of a highly crystalline order and have a peculiar and distinct general appearance different, as a rule, to those of any subsequent geological periods and so not easily mistaken for them, consisting in the lower division, mainly of granite, gneiss and schists, and in the upper divisions of gneisses, schists, quartzites, slates, some marble, serpentine, etc. The upper or Pre-Cambrian series is not nearly so universally found as the Laurentian or Archzan roper. In Colorado we find the Pre-Cambrian represented ocally in South Boulder and Coal Creek canyons, along

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the foothills, also near Salida in the Arkansas valley, in the Quartzite range and on the road between Ironton and Ouray in the San Juan Mountains, The new Kootanie silver mining district of British Columbia, seems to be largely in these PreeCambrian rocks. This Pre-Cambrian is usually very thick, numbering many thousands of feet.

It is distinct from the Archzan proper or Laurentian by lying on the latter at a different angle, in other words "unconformable." The rocks, too, do not contain so much of the heavy massive granites, and heavy bedded gneisses as the Laurentian, but are more characterized by quartzites, by conglomeratic gneisses and schists, and show clearly that though highly metamorphosed and crystalline,' they

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PLATE III. Archzan Rocks.

are of true fragmental and aqueous origin, for the pebbles in the gneiss are often very distinct, and ripple marks are not uncommon on the quartzites and slates and schists. The material was doubtless derived by waters from that of the underlying and older Laurentian. The whole Archzan series, however, has evidently passed through an ordeal of heat, such as is called aqueo-igneous heat, and all its elements are in a highly crystalline condition. Its strata are intensely folded and crumpled. See Plate III.

Signs of life, in the upper series even, are exceedingly obscure and doubtful, such as graphite and possibly corals. Great iron beds also occur, indirect proofs perhaps of the previous existence of life.

We have been thus particular with this Archean Age because its rocks are of great importance to the prospector, being the main repositories of gold, silver and the pore metals thoughout the world. Moreover many of the other and newer rocks containing gold and silver have been made from the detritus of this, and the gold placer beds largely from the detritus of the rocks and porphyries found in this age. Thus the Archzan may be considered as the parent of nearly all the other rocks. When later we have studied the origin of ore deposits, we shall see how eminently the Archean Age with its attendant heat, chemical reactions, fissuring, metamorphism and volcanic eruptions was favorable to the diffusion and concentration of precious ores in its rocks,

Cambrian And Silurian Ages,

Cooling and consequent contractions still progressing in the globe, fresh and greater wrinkles and corrugations were caused on the surface of its crust, and soine of these granite seabottom strata were crumpled up, till the crumples arose above the then universal ocean as low islands or reefs. The ocean had by this time cooled sufficiently to support low forms of marine life, and so along the flanks of these granitic islands, corals formed reefs, shell fish swarmed and sea weeds grew. Sands formed by the waves from the material of the granite were laid down as shore-line beaches, often mixed with shells; and in deeper water, corals were forming limestones as at the

resent day, both, by time and pressure, consolidating into

ard rock, eventually it may be, metamorphosed by heat into a semi-crystalline hardness, as in the case of the Cambrian quartzite and Silurian limestones, the latter sometimes changed to marble. If these Cambrian quartzites were formed from the detritus of the granite and the granitic series is the source of gold, it is not surprising that we find the Cambrian quartzites /ocally rich in gold, as they were the auriferous sea beaches (like those of to-day in California which are gold bearing) of that period, later consolidated into hard rock. In Colorado the Cambrian quartzites are only locally prolific in gold, as at Red Cliff, but as they have hitherto been much overlooked by prospectors they are worthy of closer attention by the goid seekers. The limestone not being. of a true fragmental origin but formed by the slow work of corals, could not be expected on consolidation to be a recipient of gold, but

jater by its peculiar chemical composition, of which we will speak hereafter, and by its cavernous nature, it furnished a more convenient receptacle for silver and lead ores,

So then in Colorado and in other regions, we find first the upheaved crumpled granite of the old Archzan island, and on these the Cambrian sandstone or quartzite beach of "golden sands" with some fossil shells, and upon this again Silurian limestone with relics of fossil corals and shells. So we call these ages the Cambrian and Silurian because the fossil shells and corals are peculiar to those ages and distinct from those of later periods or the present day.

Plate Iv.

America at Close of Archzan.

North America at the beginning of these periods was barely outlined by a few granite islands congregating mainly in the region now occupied by Canada, whilst one or two reefs or scattered chains of islands marked the site of the Eastern ranges of mountains, and a few parallel granite islands outlined the site of the principal uplifts or future great ranges of the Western Cordilleras. All else was ocean, and that ocean was depositing its Cambrian beaches and Silurian coral limestones against or near these granite islands destined in time to grow into lofty mountain ranges,

and to become the backbone of the American Continent. See Plate IV.

Devonian.

The Devonian which should come next in order in the geological tree appears to be absent in Colorado but is well shown at the Eureka Mines in Nevada. The rocks appear to be mostly r:arine limestone full of corals and shells anda few remains +f gigantic fishes for which this age was celebrated. Land plants and some coal are found in it in the East. Lead silver ores may be expected in the limestones of this age, and in Cornwall (England) Devonian slates traversed by quartz porphyries are the main rocks carrying tin ore, a metal very scarce at present in North America,

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PLATE V. Section showing Unconformity of Geological Eras.

These ages we are speaking of are separated or distinguishable from one another by decided and characteristic changes in the fossil, animal and vegetable life existing between one age and another, also in some countries by marked unconformability of the rocks, z. ¢., the rocks of one age lying at a different angle upor the upturned rocks of a previous age marking great oscillations between sea and and,

In America, however, these oscillations between sea and land seem to have been less than in Europe, and we find a general uniform rise of the continent from the primitive oceans, and an orderly succession of strata lying against the flanks of the ever rising granite nucleus of both mountains and continent. Hence to distinguish the different ages we are driven more to the study of fossils and lithological peculiarities than deriving any help from observed marked uncontormability. See Plate V, in which the strata of the

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different eras lie upon one another at different angles, and the glacial and Quaternary drift pebbles and clays are strewn unconformably also over the tops of the uptilted and eroded strata of all the eras beneath.

Carboniferous,

In the Eastern States as the American continent gradually rose from the sea, and to the granite islands had been added a Cambrian, Silurian, and Devonian shore, with further unequal elevation, a kind of wide trough or synclinal fold or depression appears to have been formed between the middle and eastern part of America, which was at first occupied by a wide arm of the sea, later, by continued elevation, by a great body of fresh water, and later by low marshes and low marshy islands barely above sea-level. Upon these low lying lands grew a dense vegetation unlike any of the pr sent day, but resembling somewhat the tree ferns of our southern semi-tropical States. This low lying region was subject to freshets and inundations from the surrounding higher regions, periodically deluging the swamps and swamp vegetation with river and flood deposits of pebbles and sand, under pressure of which the peat gradually turned into coal. Successive coal seams were formed by successive growths of vegetation between the intervals of periodic inundation, or of subsidence and possibly at times of upheavals, for these low lands, as sediments accumulated, appear at times to have sunk below the sea and again to have been either built up above it by fresh supplies of sediment, or to have been temporarily raised up by upheaving forces.

Finally by a grand revolution which closed the Carboniferous age in America, the coal swamps with their coalbeds and strata were crumpled up to form the present great Appalachian Chain.

Similar movements no doubt took place about the same time in the Rocky Mountain and Western region. But here the marine condition seems to have predominated over the fresh water one, for we find the Carboniferous in Colorado more represented by marine fossiliferous limestones and sandstones than by those of fresh water origin, though the Weber-grits may have had a fresh water origin, as in a few rare instances we find fossil plants like those in Pennsylvania together with a few insignificant small seams of coal. But in the West it is evident that the circum-

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stances from one cause or another were not favorable for the production and growth of extensive coal-beds as in the Eastern States. The coal forming time was reserved in the West for a much later period, viz.: the Laramie or Upper Cretaceous. The Lower Carboniferous in Colorado, however, contains in its limestones much of our silver-lead wealth as at Leadville and Aspen.

The Cambrian, Silurian, Bevanian, and Carboniferous Ages have been grouped together by geologists into one great era, the Paleozoic, owing to a general family likeness in the fossil fauna and flora of these ages.

To the Archwan and Paleozoic rocks the bulk of our veins and deposits of gold and silver are mainly confined, though both in Colorado and elsewhere, as will appear later, if certain peculiar conditions are present, the rocks of the later and newer periods may also in some regions produce precious ores. But the prospector should give his closest attention to these o/der rocks, hence we have devoted extra space to their description and history.

Triassic And Jurassic, Or Jura-Trias,

After the Carboniferous, followed the Triassic and Jurassic; sometimes in America, owing to the difficulty of positively separating the two periods, they are combined under one name, the Jura-Trias, and in Colorado are locally called the " Red-Beds," owing to their prevailing red and variegated colors. The series is well represented in the celebrated Garden of the Gods, near Colorado Springs. The red conglomerate sandstone of the Trias proper, has so far yielded no determinative fossils, but the variegated clays in the upper Jurassic at Morrison and elsewhere have yielded some remarkable Saurian remains of land lizards. It is probable from the presence of salt and gypsum in these red-beds, and the prevailing redness of the rocks, due to iron, which was not leached out through the agency of organic life, and the general absence of fossil remains, that the lower portion of these rocks was laid down in landlocked salt seas, or salt lakes, shunned by both vegetable and animal life. The upper portions, however, show evidence of the existence of land of a low marshy character, with fresh water and probably large estuaries, as we find the remains of turtles, crocodiles, fresh water shells and Dinosaurs or land lizards. The rocks of these periods are not generally prolific in ores. The Silver Reef sandstone of

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Utah is an exception, which contains chloride of silver disseminated through it. When pierced by eruptive rocks, however, ore should be looked for in this series as elsewhere,

Cretaceous Period,

Upon this followed the Cretaceous, a series of very thick formations, numbering several thousands of feet in Colorado, consisting in its middle portion of limestones, and thick beds of drab shale, These are mostly marine, as shown by the sea shells in them, but at the base is what is called the Dakotah group or Cretaceous No, 1, a prominent

Plate Vi.

North America in the Cretaceous.

sandstone jogback in which the fossil impressions of leaves, very like, but not identical with those of the present day, show that land and fresh water existed at the time. The limestones and clays of the middle or Colorado group, contain quantities of fossil marine shells, such as_ the Nautilus, Ammonite, Baculite and Inoceramus.

The Laramie forms the upper group of the Cretaceous, and contains our principal western coal fields and abounds. in fossil remains of tropical foliage.

This Laramie group marks an important era in our Rocky Mountain region for it shows that beginning of the great Rocky Mountain revolution, by which the granite islands

before mentioned, against which all the previous sediments had been forming mainly beneath the sea, were elevated 10,000 feet or more into continental or mountainous masses, dragging up with them portions of the sea bottom and exposing it as land surface, dra.uing off the shallow Cretaceous sea which had hitherto divided the Eastern half of the American continent from the Western, bringing on a land and continental condition, which was completed in the following Tertiary age and has continued to the present. See plate VI.

The Jurassic, Triassic and Cretaceous are grouped into one main division called the Mesozoic or middle lite era of the world's history, None of the rocks of this age in Colorado are celebrated for ore deposits, except locally under local conditions.

In California and portions of the extreme West where these rocks have been highly metamorphosed by heat and penetrated by igneous rocks, some of the leading ore deposits of gold and silver are found, The same remark applies also to the succeeding Tertiary in those regions, particularly in the Sierra Nevada and Coast ranges.

Tertiary.

The Tertiary age seems in the Rocky Mountains to mark an era of comparative rest in mountain elevation, for the strata forming some of the divisions of this age lie almost horizontally upon the tops of the earlier upturned periods.

These beds were formed by fresh water lakes in Colorado surrounded by tropical vegetation. In the Coast ranges of California the Tertiary is upturned into mountain formsand metamorphosed, and, from the presence of sea shells, is clearly of marine origin. The Tertiary in Colorado is best seen in outlying table lands. In Wyoming the Tertiary lake formed the Green River beds and Bad Lands abounding in fossil mammals, leaves, fishes and insects. The Tertiary was the world's tropical summer, a period of beautiful lakes of semi tropical foliage and a warm climate. In certain regions it was disturbed by gigantic revolutions which upheaved the Himalayas and the Alps. Such revolutions as occurred in our Western Cordillera system were marked by enormous ebullitions of lavas of various kinds issuing from fissures deluging Idaho, Nevada, part of Oregon, and Washington. Remnants of this same disturbance are seen in the form of basaltic overflows capping Tertiary strata in Colo-

irk he ost yds. ido s of and 5, 1S yest ake io in iary hkes tain up- $s as id by rom ash- h the Folo-

rado and New Mexico; and the vast volcanic region of San Juan in Southern Colorado is covered with successive lava overflows of the same period.

The Tertiary rocks in Colorado are not generally good prospecting grounds. The lavas, however, are (with the exception of the basalt, which for some reason is generally sterile) locally productive, as for instance the entire San Juan Region, also Cripple Creek Mining Camps and Silver Cliff. So, the prospector, whilst he need not waste time among the sedimentary beds, will do well to examine any eruptive rocks of this period for gold especially, and also for silver. The varieties of lava are principally andesite, rhyolite, trachyte and basalt. In the Coast range of California where the Tertiary beds have been metamorphosed by heat into slates, goldand cinnabar are found.

Glacial Epoch And Quaternary Age,

The Tertiary Summer was closed by the worid's Great Winter. The ice from the north pole for some reason we will not discuss, extended its domain far south to latitude 40. All the northern temperate regions of the world were ice-sheeted and the sheet extended itself as by long fingers down the, by that time, highly developed mountains, filling the ravines with glaciers. By the downward destructive grinding motion of the glaciers, the ravines, commenced by water, were deepened and widened by ice. Fissure veins were thus exposed, both of gold and silver. The debris from their progress the glaciers carried on their backs and dumped at the outlet of the canyons; and when the temperature finally became warmer, and the glaciers melted, all the long lines of traveling boulders scattered upon their backs, many of them containing gold robbed from the veins, were left as banks or "moraines" forming our "gold placer" grounds along the sides of our streams and canyons, or sometimes a thousand feet above the present river bed, marking the original height orthickness the great ice bodies once attained.

So were our canyons largely formed, and so did our gold placers originate. After the Glacial Epoch, a warmer period set in, called the Quaternary. The ice melted. Vast bodies of fresh water were distributed in wide streams and monstrous lakes over large portions of this hemisphere. The rough " morainal'"' dumps of the glaciers were "sorted." or "modified" by water, rolled into pebbles and sand, and re-

distributed along the banks of streams or carried out into beds of lakes. In these pebbles and sand, was much of the precious metal mined and robbed from the veins. The gold by its insolubility remains to this day in our placer beds and "drift" or "wash" and is collected by hydraulic mining. That the prospector for gold should closely study these Glacial and Quaternary deposits is evident.

So ends the history of our section. Still the agencies of nature are at work as of old. Continents are gradually rising or sinking. Mountains are being imperceptibly elevated. Water is still sculpturing them with canyons. Rivers are carrying down fragments robbed from the land and depositing them in the ocean to form strata for future continents,

The fires of the earth are not yet dead, for volcanoes still vomit lava. The earth, however, is still continuing to lose internal heat. Its crust is still contracting and wrinkling itself upwards, for we find modern sea beaches raised high on our seaboard cliffs. Shocks of earthquakes from time to time, prove that motion of some kind is going on beneath us, and doubtless our mountains are still rising imperceptibly, as they appear to have done in ages past, giv 9¢ additional lifts and elevation to old uplifted strata, and slowly elevating newer strata that since the Tertiary have lain apparently undisturbed. We say apparently, for not only are the Tertiary beds uplifted from 5 to 10 degrees, but even the more recent Quaternary deposits, showing that movement has been going on comparatively recently and may still be progressing imperceptibly.

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Chapter Iii.

The Prospector'S Paleontology Or Study Of Fossils.

A prospector in his roaming among the rocks is, likely from time to time to come across a good many fossils or 1. petrified remains of life that once existed on this planet. i fe will feel curious to know what these are, what class of animal or vegetable they may represent, to what geological €ra, epoch, or subdivision they may belong.

Sea is Ssh al ace ated

Neti 8.

Characteristic Rocks. M.Verals, Metals G6. — Fossils.

Oes

Placer Gold \Yebhants eet, Bon

Loosely Stratified Ord Gola Placers Conglomerates.5anas| in California

OE Lava-GolagSiverbeari S Thin Li nie Coal es Fossil Leaves MeramnOrds osed Sandstone M. Rd ; arina (5

S sandstones Cale hearing sy) vA IN California also F ; SOE Shales § C/ays Asphalt ia California

aétritus omesor 7 Colorado Marine Shell.

and California BEE OELES

_Granitic detritus

Gi ll Y Beds Sanrdstones

Coal

Leaves, ICES &¢. Sea Shells

& Drab Shales, Clays \Canon Ciiy O Horizon Seaphites Bacuylites + . Sla SHEMS

S Limestone Flux Lime Inoceranmus Dark sales Clay, ron stone OVSIErS

oS Lakota Conglomerate Sandstone Fire Cla Leaves of Trees S

ONQOINE/ a Ut 0

Yar) ated Clays GYpsuin Ditiosaurs COlO

baa bana one arg Lie ome Sea Usha Myon

Uh Lime Stones ye PRE - Tick hea conglomerate sHee? eee LES, nq Faatarlmhs of SAUNAS

reddish Conglomerate Lastén Coal Beds

Shales, Janadstones Grits & Shales

Corals Blue Limestone Silver, Lead AMM WNC,

édash Sandstone Eureka, Nevada Sta Shells Lime stones Jilyer, Lead Fish Corals

Marble

fastern Coal of Pennsylvania Land Plants

8 Gyboriferous WWriassic

Fpaicozoic

Drab Pale lLimestone| ilver, leat' Ja SREMS bolonteé y Cruslacea fon Triloites Corals

Wales Quartzites

— Gold, Silver a y Few Poste ANS Granite, Gnel5s Lead, int, Copper Ye SGIS OF Life SX hist, Wyenile /ron

PLATE VII. Prospectors' Geological Table of Western Formations, Showing Principal Characteristic Rocks, Minerals and Fossils to be Found in Them.

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Fossils to a geologist are the labels of the rocks; show a geologist a fossil, and he will probably be able to tell at a glance whether the fossil came from a series of Paleozoic, Mesozoic or Cenozoic rocks, whether it belonged to a very ancient geological period down near the primitive granite, or to a comparatively recent one near the modern soil, high up in the geological scale and nearer to the life of the present day. He may be able to tell not merely whether it belongs to one of the great divisions, to the great eras, but also to the subdivisions of these eras, whether to the Silurian or Carboniferous, the Jurassic or the Cretaceous, or even to minor divisions of these, called groups; whether, for example, it belongs to the Dakotah group of the Cretaceous, or to the Laramie group of the same period.

Practical Use Of Fossils.

The practical use of a general knowledge of fossils is obvious. prospector finds in certain strata a fern-leaf of the Carboniferous, this tells him he must be on the coal strata and forthwith he hunts for coal. Or he finds a Paleozoic shell or coral which points to the fact that he is probably in the neighborhood of the precious ore-bearing rocks.

Later perhaps he finds a shell or coral characteristic of the lower Carboniferous blue limestone, the celebrated leadsilver bearing formation of Colorado and the West, and he is encouraged to look for these ores. The limestone by itself is but a poor guide, for there are many limestones not unlike it in the different series of rocks, but this particular shell labels this as "¢ke blue limestone" and no other. Hence a characteristic fossil may help considerably in following up in its extension an ore-bearing rock, and not only that locally, but in regions very far apart. Soon after the celebrated ore deposits of Aspen were discovered, and the mines were in their infancy, some fossils were discovered that showed the deposits to be in the same limestone as that at Leadville, which had proved there so productive. This gave an additional impetus to the camp, "a second Leadville" so it was said.

Again, though a prospector may not find at once the particular geological stratum or period he is looking for, if he finds a characteristic fossil anywhere, in some other period, he knows from it whether the period he is after lies geologically belov, or above where he is looking.

Thus, if a prospector finds a Silurian shell he knows that the Carboniferous "blue limestone" must be close above this Silurian, or if he finds a Marine Cretaceous shell, he knows that the Laramie coal-bearing group lies above. On finding a Cretaceous or Jurassic fossil, he knows that the Carboniferous and Paleozoic series must lie considerably below him.

In the accom~anying geological table, Plate VII, we have shown what rocks and what minerals and metals are likely to he found in the geological divisions and subdivisions ; also, generally, what classes of fossil life are to be expected in each.

Then in the diagrams of fossils, we have selected pictures of the fossils most commonly to be found in all the great divisions, so that if the prospector finds a fossil, he may, by comparing it with the pictures, find what its name is, and to what great geological division or subdivision it belongs ; it is not so necessary for him to remember the scientific "'jaw-breaking " names of these fossils, as it is for him to be able, at sight, to recognize whether it belongs to one or other of the great eras, or, better still, to one of the minor subdivisions of these; whether it is Paleozoic or Mesozoic, whether Silurian or Cretaceous, whether it belongs to the Colorado-Marine-Cretaceous or to the Laramie fresh-water Cretaceous, etc. If the fossil is a very peculiar one and can not be identified as belonging to any of the common ones we have pictured, he had better send it to the office of the U.S. Geological Survey at Washington, or to some good paleontologist. We frequently have fossils sent to us to know whether this or that fossil is a likely indication of the presence of coal or other mineral, and sometimes our identification is a material help to the prospector; but with the above table the prospector could save himself the trouble and postage stamps.

a ARCHAAN,

Starting then from the Archzan as a sure and safe horizon, the prospector will find no fossils, and only some indirect probable evidences of past life, such as graphite, which may possibly represent ancient coal derived from some form of vegetation unknown to us. Limestone and marble are also indirect evidences of past organic life, most modern limestones being due to the remains of corals, etc. Whatever life may have existed in those primitive granitic

rocks, has been pretty well obliterated by excessive metamorphism and crystallization of the strata,

Cambrian.

Resting on the granite he finds the "Primordial" or "Cambrian" series, sometimes called the Potsdam Sandstone. If this series consists of unaltered sandstones, he may be fortunate enough to find some of the shells and

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Plate Viii.—Cambrian Fossils.

1, 2, 3, Trilobites; 4, Track of Crustacea ; 5, Track of Worm; 6, 7, Sea Shells.

other traces of life of those old beaches as shown in the diagram, but generally speaking, in Colorado and the West, the Cambrian is so highly metamorphosed and altered into hard crystalline quartzites, that evidences of past fossil life are as scarce and indistinct as in the Archzan, and probably for the same reason. The forms he may find are, a little crustacea called a Trilobite, something like a "sand crab," ae few little shells and some marks of worms. Plate

Silurian,

In the next series, the Silurian, he may be more fortunate. He may find remains of sea-weeds, corals and shells and fragments of a sort of sea-worm called a Crinoid, or sea a The little discs with a hole in the center forming a little ring about the size of a pea, constituting the discs or rings,

Tetas

Cie

Plate Ix. —~Silurian Fossils,

1, 2, Orthis; 3. 4, Spirifer; 5, Pleurotomaria; 6, Murchisonia; 7a, 74, Trilobite (Calymene) ; 8, Coral Fenestella ; 9, Coral Choetites ; 10, Graptolite; 11, Orthoceratite.

of which the stems of the sea lily are composed, are sometimes very common in Silurian and Paleozoic rocks, though it is rare to find a complete Crinoid, and especially the beautiful comb-like flower or head of the sea lily. He is likely to find also a more advanced type of the Trilobite and various Spirifers and other shells as pictured. Plate IX.

Devonian.

In the Devonian he may find the teeth or bones of fishes, and a few remains of peculiar land plants, neither of which are known in the Silurian below, also many corals.

Plate X.—Devonian Fossils.

1, Spirifer ; 2, Comocardium ; 3, Orthis: 4, Goniatites ; 5, 6, 7, Corals ; 8, 9, 19, Fish Teeth; 11, 12, Fish Scales.

Carboniferous.

In the Lower Carboniferous "blue limestone," corals and shells appear, especially Spirifers and Productus, together with Crinoids and a very simple curled shell like a snake coiled up, a " Goniatite," one of the earliest of the Ammonite class. At Aspen, associated with the ore deposits we found in the blue limestone most of these, together with a kind of snail shell called Pleurotomaria. At Leadville in the same

Rioaiaitie ARs bs he

formation Spirifers and Productus are occasionally found. A very curious coral is one shaped like a screw, called Archimedes, after the author of the screw. Cup corals are common,

In the Middle Carboniferous, associated with the coal seams, many curious remains of reeds, ferns and other aquatic plants of that age are found, but these are scarce in Colorado and the West. The prospector will observe that

Plate Xj.—Carboniferous Fossils,

1a, 14, 1c, Productus; 2, 2, Spirifers ; 3, 3, 3, Rhynconella; 4, Euomphalus; 5, 5, Crinoids ; 6, Pleurotomaria ; 7. Bellerophon ; 8, Athyris Subtilita ; 9, Astartella ; ro, Goniatites ; 11, 12, Corals; 13, 14, 15, 16, Plants; 17, Spine of Echinus.

there is a general family likeness between the fossils of each division of the Paleozoic and in the Paleozoic as a whole, and it may not always be easy for him to determine whether a shell is Silurian, Devonian, or Carboniferous, but of one thing he will be certain, that it is Paleozoic.

af ! a : ¥ t

Triassic.

In the Trias throughout the West, he is no* likely to find many fossils, the rocks are generally too coarse, but in the Eastern States, though he ney not find any true remains, he may observe the tracks left by great Saurians, as they walked on their hind feet, or on all fours, on the red sands of the beaches of those dreary salt Triassic seas, leaving "footprints on the sands of time" full of interest.

Jurassic,

In the Jurassic shales and limestones in Colorado, he may be equally unsuccessful, though in the upper Jurassic just

Plate Xii,—Jura-Trias Fossils.

; 2, 3, Foot and Shoulder Bone; 4, 4, Vertebra of Sea Saurian, Ichthyosaurus ; 5, 6, 6, Teeth of Saurians ; 7, Belemnite ; 8, Echinus 9,9, Ammonites; 10, Exogyra; 11, Trigonia Shell.

1, Dinosaur Lizard ;

below the Dakotah sandstone, he may light on the bones of

gigantic Dinosaurs, or great land lizards, such as the author ound in Colorado and Wyoming, monsters 60 to 80 feet in length and proportionally tall, standing from 20 to 25 feet in height. In the lower puree in Wyoming, he will find great numbers of sea-s

ells and Ammonites, and a'*round

shell like a cigar called a" Belemnite" or spear-head, the internal shell of an ancient cutie fish, Plate XII,

Cretaceous,

In the Cretaceous, beginning with the lowest group, tlie: Dakotah group, net-veined leaves of deciduous trees, such as the willow, oak, maple, etc., the earliest known leaves of pose kinds of trees, may be expected in the sandstone and clays,

Plate Xiii.—Cretaceous Fossils.

1, 1, Inoceramus ; 2, Cardium ; 3, Corbula ; 4, Mactra; 5, Margarita; 6, Fasciolaria ; 7, Anchura ; 8, Pyrifusus ; 9, 10, Scaphites ; 11, Criocera' ; 12, Baculites ; 13, Shark's Tooth,

In the Colorado group of the Cretaceous, above the Dakotah, abundance of oyster shells and large clam shells: (Inoceramus) are sure to be found in the limestones and ie marine shales. In the Montan. group of the Cretaceous. above this, consisting mainly of drab shales and some sandstones, great quantities of sea-shells are found, amongst them various peculiar forms of the Ammonite allied to the modern nautilus, and called Scaphites, resembling snakes.

or worms uncoiling, together with shark's teeth and bones of sea Saurians.

In the sandstones of the Laramie Cretaceous remains of sea-weeds are found; in the sandstones immediately below the coal-beds, and in those associated with or above the coal, are found great varieties of semi-tropical leaves, such as those of the palmetto, fig, beech, elm, magnolia, sassafras, etc, The presence of these leaves isa pretty sure indication of coal,

Tertiary,

In the Tertiary fresh-water beds, similar leaves and thin beds of poor lignite coal are found, together with fossil

Plate Xiv.—Tertiary Fossils.

1, Palmetto; 2, Cinnamon Leaf; 3, Cardium ; 4, Insect ; 5, Nummulite Shell ; 6, 7, Fresh-Water Shells,

Quaternary Fossils.

8, Mammoth Elephant's Tooth; 9, Mastodon's Tooth; 10, Flint Implement ; 11, Stone Grooved by Glacier,

insects and remains of mammals, In the Marine Tertiary are sea-shells.

Quaternary,

In the Quaternary drift, amongst the pebbles, sands and "wash" characteristic of gold placer beds, an occasional tooth, tusk, or bone of the great hairy Mammoth elephant or the Mastodon elephant may be discovered, together with the stone implements or bones of prehistoric man and pebbles grooved hy glaciers.

Chapter Iv. Prospector'S Lithology Or Study Of Rocks:

The

His busi-

ector wants to know a great deal about rocks, ant companions in the field,

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Eruptive Rock Porphyry

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Plate Xv.—Characte

a, Sedimentary Rocks Tipped up Against Intrusive Porphyry Laccolite; 8, C, Basalt Capping Soft

Shales :

Ristic

Appearance Of Rocks In The Field.

D, D, Distant Granite.

He wants to be able to recognize

ness is amongst rocks.

bble, or confronts

a loose pe

them at sight, when he picks up

Aat

Plate Xvi.—San Juan Volcanic Plateau Mountains.

a mighty cliff. When travelling over the mountains, as he surveys the grand panorama from the top, he wants by the peculiar forms and patterns each variety of rock is apt to take as the result of erosion and weathering owing to different degrees of hardness, to be able to make a shrewd guess from a long distance, as to whether one moun- ; tain is made of granite, or another of limestone, a third of por- & phyry. This habit of forming ¢ rough guesses as to the character of distant rocks, decides him as to choosing his course for g prospecting. 'In those sharp , granite looking peaks" he says, 'may be I will find fissure veins. Yonder cones, like the spires and minarets of a Gothic cathedral must be porphyry or igneous rock, another likely locality, and mark where they break through % the sedimentary strata, and tip 2 them up all around them; at the Z% junction of these sedimentaries ' with the igneous rock, there may be lime-stone, and a 'contact blanket deposit. Yon smooth grassy slopes are probably underlaid by sandstone or limestone, and the rolling valley beneath by soft shales. The latter are unpromising for precious ores," Or, again descending from his perch into the canyon below, he recognizes the granite basis, and on top of it, a series of sedimentary rocks. The lowest of these, by its rusty-white, masonry-like structure, he judges to be Cambrian quartzite, the thin-bedded strata above, Silurian limestones, and

ranite

a

ssion of Lava Sheet

a Succe

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the heavy massive beds above these, Lower-Carboniferous blue-limestone, whilst a dark greenish-gray rock, running in and out irregularly among the strata, sometimes between

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the stratification planes, at others cutting across them, he judges to be an intrusive sheet of porphyry, and looks again for "contact deposits." A rock running up like a low wall from the bottom of the canyon to the top, may be either a

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quartz fissure vein, or a porphyry dyke, and well worth examining, There are many ways of studying rocks, one by hand specimens, finding out all the minerals composing them, and then naming the rocks from which they came; another by observing the appearance of large masses of roc'* 'n the field, and noting their mode of occurrence ; anu taly if we wish to be very accurate, making thin microscopic sections and a chemical analysis, but for the average prospector these last will be rarely necessary,

If a prospector bought a manual to study rocks, for practical purposes, he would find himself amongst a sea of names of varieties of rocks, nine-tenth of which it is safe to say he would never meet with in his field experience,

To save him the trouble of wading through such books, we select just about as much as a prospector is liable to meet with in the field or find practically useful, saying little also about such common rocks as are familiar to every one,

Those that need most definition and are of most importance in the mining field, are the crystalline rocks, belonging to the class called metamorphic and igneous; the last especially needs careful determination.

Nearly all sedimentary rocks (limestone excepted) are derived from fragments of igneous and metamorphic rocks. Probably nine-tenths of the sedimentary rocks are derived from granite alone, the remainder from the igneous rocks, such as porphyry, basalt, etc. By describing the parent rock, the derivative one is more easily made out.

Rock Making Minerals.

Crystalline rocks are made up of certain distinct minerals, most of them of quartz, feldspar and mica with sometimes also hornblende and augite. Other minerals may locally occur as occasional elements.

QUARTZ scarcely needs description being so well known.

The hexagonal prism of this crystal is too hard to be scratched with a knife and will scratch glass. This distinguishes it from calcspar and barite, for which it might be mistaken in the field, moreover it will not effervesce with acids.

THE FELDSPARS are nearly as hard as quartz. Their colors are white, greyish and flesh-color, They are rarely as transparent as quartz, being generally opaque. Their form of crystallization is different from quartz, and ina vein they show one smooth face of their crystal, whilst the quartz is

more like crushed loaf-sugar. Ina porphyry the feldspar crystals are very distinct, and give a characteristic spotted appearance to the rock. Two varieties of feldspar are characteristic of the crystalline rocks, one called orthoclase or common feldspar, a potash-feldspar, the other called oligoclase, a soda-lime-feldspar. The former is very characteristic of granitic rocks as well as of igneous porphyries, the latter is rather more characteristic of more recently erupted igneous rocks, such as diorite, basalt, andesite, etc.

Orthoclase is generally in large crystals, oligoclase in small. When the crystals are very small, it may take a microscopic examination to determine to which variety of feldspars they may belong. The oligoclase and plagioclase crystals in igneous rocks are commonly but little white dots.

To determine accurately, microscopic slides and chemical tests must be made, but this is scarcely within the scope of the prospector who wants to guess roughly at sight as to the name and character of a rock.

Mica, both black and white, needs no description, HORNBLENDE differs from mica in being of a duller lustre and of a different form of cry stallization as shown in the plate. The color is a greenish-black; the greenish tint is

distinct, when the crystal is struck by a hammer.

AUGITE or PYROXENE is scarcely distinguishable from hornblende. In Colorado, augite is mainly confined to two kinds of rock, basalt or dolerite and andesite, both of comparatively recent volcanic origin. Hornblende and mica are common to nearly all the metamorphic and igneous rocks.

TALC amongst miners means almost any soft, sticky, or slippery, decomposed rock, but strictly, talc is q pale green, soft mineral like mica and isa silicate of magnesia. Steatite or soapstone is massive talc. Miners often wrongly

call any soft clay or rock, soapstone also.

CHLORITE is another magnesian mineral, of a given and soft character. Chlorite is again a name given to almost any greenish rock of a schistose and soft decomposed character,

CALCITE is carbonate of lime crystal, the element of limestone, and is distinguished by softness and effervescing in acids,

DOLOMITE or carbonate of lime and magnesia is very like calcite and is the element of dolomitic or magnesian limestone. Dolomite effervesces with much greater difficulty than true limestone. To effervesce, the dolomite should be powdered, and the acid heated.

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GypsuM or sulphate of lime can be distinguished by its extreme softness, being scratched by the finger nail; it does not effervesce like lime.

BARITE or "heavy spar" oc-

ae ft 1 curs in some veins, but not as

: a constituent of rocks, It

. looks like calespar, but is

heavier and will not effervesce with acids,

IF LUOR-SPAR occasionally occurs in veins, in cubes or massive. It is easily seratched with a knife; its colors are green, purple, yellow, blue or white.

GARNETS, GREEN EpPIpoTer, BLACK TOURMALINE,and other minerals or gems may occur, but not as important constituents of the rocks.

Crystalline Metamorphic Rocks,

GRANITE.— Beginning with the granitic series of the Archwan age, granite proper is massive, shapeless, or amor-

PLATE XVIII, phous and shows no bedding

1. 'Igiclinic Oligoclase Feldspar. 2. planes or other signs of former Monoclinic Orshociase: Faliapat, 2 stratification. It is thoroughly DP eroniE sere icmbinde crystalline : like Jump-sugar.

By some it is considered a true igneous rock, one that has been thoroughly fused by heat, as much as the lavas or molten iron; by others its crystalline amorphous condition is supposed to be the result of extreme metamorphism of originally sedimentary bedded rocks, such as gneiss or schist, the two latter being sometimes traced down through a gradual change into granite. The composition of granite is mica, quartz and feldspar with sometimes a little hornblende, The micas may be white mica (muscovite), or black mica (biotite), Both orthoclase and oligoclase feldspar may be present, but more commonly the former, which is often a pinkish flesh color, Granite, in its crystalline texture, differs both in character and appearance

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from porphyries and other igneous rocks, in the fact that its crystals are all jumbled up and crushed together like loaf-sugar, and none of the crystals are set like plums in a pudding, distinctly in a backing or paste of very small crystals of amorphous or glassy material, as in the porphyries or igneous rocks, Granite is probably th oldest and deepest rock known. It is often traversed by sparry veins, both great and small, which consists of quartz or feldspar or both, in a more sparry condition than when diffused through the parent fot,

These so-called "quartz veins" are often called "granulite" or "pegmatite" or "graphic granite." The quartz and feldspar are often arranged in parallel] plates, giving on

Peamartir , . GRANITE oats SYENITE

Plate Xix. Plate Xx. Plate Xxi.

cross-section Curious marks like Hebrew characters, hence the word graphic. The bulk of our so-called quartz fissure veins in the granite mountains may be called pegmatitic veins, The colors of granite vary from reddish to gray, or nearly white to black, according to the preponderance and colors of the micas and feldspars in them,

SYENITE is little more than granite in which hornblende supplies the place of mica.

GNEISS may be called "bedded granite," showing a bedded appearance. mn

Guess Gneiss is often curiously goytaarcoMica Schist PLATE XXII. and prettily banded or PLATE XXIII.

streaked by seams of mica c dove-tailing into each other. If mica preponderates, it is called "mica-eneiss," if hornblende " hornblendic gneiss."

SCHIST niay be called laminated-gneiss or granite, being finally divided into lamina or leaves. This foliated structure is due to the arrangement of the flat-lying crystals of mica or

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hornblende largely composing it. It may be a mica-schist ora hornblende- .chist.

SLATE is shale altered by heat into a hard crystalline structure,

QUARTZITE was originally a sandstone composed of quartz grains, which by heat have been partially fused together at the edges, resembling granules of tapioca in a tapioca pudding. Quartzite differs from quartz in being a rock made out of pieces of quartz, and not the original mineral itself. Quartzite may be white like sugar, grey, brown, or rusty. [t shows a true stratified structure.

MARBLE is limestone similarly changed to a more crystalline condition.

SERPENTINE isa green magnesian rock, sometimes found with marble and igmeous rocks and is formed by alteration of certain minerals in the latter.

Crystalline Igneous Or Eruptive Rocks.

These are rocks which are supposed to have been thoroughly fused or melted in the bowels of the earth. Some reach the surface by fissures or volcanic vents, others have never attained to the surface or overflown it, but have intruded themselves between the weak places in the underlying strata, or have collected and cooled deep down below the surface in great molten reservoirs called " laccolites" or lakes of stone. When these have been subsequently uncovered by erosion, they may present the forms of considerable mountain masses, like the Elk Mountains, and Henry Mountains and Spanish Peaks, Geologists distinguish those rocks which have poured out on the surface from craters and volcanic vents as volcanic rocks, whilst those cooling below are called Plutonic.

Intrusive Plutonic Rocks,

The component minerals of these intrusive Plutonic rocks, such as are commonly called porphyries, are principally quartz and feldspar, with mica or hornblemde. In color these rocks are some shade of grey, green or maroon, oreven white, but their most striking characteristic is a general spotted apearance. This arises from more or less large, distinct, perfect- y formed crystals of feldspar or quartz, set ina finer grained crystalline paste or background, standing out distinctly from it. This base or background may be comparatively coarsely crystalline, finely crystalline, or so finely crystalline, that the crystals can be discovered only by a micro-

scope, whilst the larger crystals seem set in the paste, like plums in a pudding. In the depths of a mine the porphyry is commonly much decomposed by water action or mineral solutions, and even passes into a clay or gouge. The characteristic spotty appearance, from the presence of individual crystals of feldspar may even then identify the rock, or by chemical analysis the very aluminous character of the decomposed rock may determine its character. When feldspar is the main constituent, it is called a felsite porphyry, : when acertain amount of quartz is present }RGRe aig a quartz porphyry. QuARTZITE (PaRTMaaniFi¢o) DioRITE, whose crystals are sometimes prarep XXIV, porphyritic in character, hence called porphyritic diorite or porphyrite, belongs also to this intrusive or Plutonian class, differing only from the others in the fact that its feldspar is of the triclinic plagioclase kind rather than orthoclase. Hornblende is a prominent constituent of this rock, and gives it, more or less, its dark, olive green tint. In appearance it resembles a dark syenite, but its occurrence as an eruptive, intrusive rock distinguishes

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Neyer ese wr PorpuyriticDiorire it, aS syenite is generally a metamorphic

(PORPHYRITE) rock. The peaks of the Elk Mountains Pare XXYV. are, many of Wheth of diorite. Diorite or 4 porphyrite is the so-called porphyry of Aspen, above the ore deposits.

QUARTZ PORPHYRIES, i These are the commonest, and may be said to be the prevailing eruptive rocks associated with our ore deposits in Colorado, as for instance at Leadville, felsite porphyries as well as quartz porphyries occur in the granite rocks in the Central and Georgetown mining districts. All these rocks are common through the West, and quartz porphyries are the most common eruptive rocks the — FecsitePorruyry prospector is likely to meet with in his search for ore deposits. We will describe PLATE XXVI. in detail one or two typical species, though it must be observed that these porphyries are of endless varieties and shades of appearance.

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noe

OuaRtz PoRPHYRY.—A quartz porphyry is a porphyry that contains quartz crystals, large or small, in addition usually to large orthoclase feldspar crystals, generally of a vitreous glassy variety called " sanidin," together with small crystals of hornblende or mica. As a typical example we take that which forms the dyke composing the yeak of Mt. Lincoln, Colorado, called Mt.

incoln quartz porphyry. This porphyry a Cg: and varieties of it are common in the y fx western mining sections of Colorado, : Fontes

In appearance it isa gray rock spotted M*™4yeoww Quartz with large and small crystals of orthoclase : sanidin feldspar, which sometimes show PLATEXXVII. an oblong face two inches long, by an inch wide, at other times a shape like the gable end of a house, according to whichever part of the crystal happens to be exposed. Sometimes two crystals are seen locked

together, forming what are called

Carlsbad twins. When the rock is de-

eo eee composed, these crystals not unfrequently drop out and lie as pebbles on

the ground, With these may be also seen rounded ends of bluish crystals like broken glass. These are portions A of perfect quartz crystals, which when LEAOVILLEWHITEQuaRTZ =extracted show a six-sided pyramid at

; either end. These larger crystals are

PLATE XXVIII. set in a crystalline ground mass of

much smaller crystals of the same kind, together with many little black cubes of shining mica, or duller lustred, longer, rectangular, oblong crystals of hornblende, This porphyry is eruptive and intrusive, occurring in dykes, intrusive sheets and laccolites.

LEADVILLE WHITE PORPHYRY.— At Leadville there is a quartz porphyry known as the Leadville white porphyry or " block porphyry " by the miners, which needs description as it is the one that more especially iS associated with the rich ore deposits. It HomwacenoeAuerre: Mion, is a white, compact, homogeneous Maine TITE, GARNET looking rock, not unlike a shaly white PLATE XXIX. sandstone or quartzite. It consists of feldspar, quartz and a little mica. Its porphyritic or

Es

spotted character is so indistinct that one would be inclined to call it a felsite at sight rather than a true porphyry, but the microscope reveals perfect double pyramids of quartz and individual crystals of feldspar set in a paste of the same minerals. It is often stained by concentric rings of iron oxide and marked with wonderful imitations of trees. The latter have earned for it the title of " photographic rock" or "dendritic porphyry." These markings are only the crystallization forms of oxide of iron or manganese, something like fern-frost on a window-, 'ne. The porphyry is very shaly, and breaks up in thin slabs; hence called also "block porphyry." It is common at Leadville and is also found elsewhere. In the same region there are many other varieties of quartz porphyry such as the "gray porphyry," the Sacramento, and the pyritiferous porphyry. The latter is often gold bearing.

Younger Effusive Volcanic Rocks,

These intrusive plutonic porphyries and diorites are generally older than the other class which reached the surface and poured over it and which may be called for distinction " effusive" volcanic rocks.

Typical of these we may cite the dark basalts and dolerites that often cap the table lands of the prairie region and overlie our coal beds. A pinkish or dove-colored rhyolite also caps some of the mesas and in certain districts an andesite lava,

DOLERITE AND BASALT.—The latter being scarcely more than a fine grained variety of the former, are very dark rocks, consisting of dark, heavy minerals, such as augite, magnetite anda plagioclase feldspar called labradorite. Such minerals are said PLATE XXX. to be basic, and the rock composing them also basic.

ANDESITE is very like dolerite, though generally a lighter gray or pink. Both augite and hornblende may occur in it, more especially hornblende, sometimes mica also. The feldspar is called andesite feldspar from the Andes Mountains.

RHYOLITE, under the microscope, shows a peculiar flowing structure, hence its name from "rheo" to flow. The lighter rocks in Colorado and the West are generally rhyo-

LO tt rt

A

ns

, mean

anaemia aseoeses

A Set

lites rather than true trachytes. Their colors are pale gray, white, pink or sometimes dark,

Rhyolite consists of a fluent, vitreous, ground mass or paste, usually containing crystals of sanidin feldspar, or even of quartz, When these crystals are conspicuous so as to give the rocks a porphyritic appearance it is called "liparite." amen

In some cases it may have even a granite-like appearance, the crystals of quartz, mica and feldspar being more or less intermixed; then it is called Nevadite, It is an acidic rock consisting of acid minerals mainly.

TRACHYTE, from "trachus" rough, is a light colored rock, with a peculiar characteristic rough feel, due to microscopic vesicularity. It consists of a ground mass of sanidin feld-

AMV@OALOIDAL ScoriA ANOESITIC BRECCIA

Plate Xxxi. Plate Xxxii,

spar and augite, containing crystals of the latter. In ninetynine cases out of a hundred in Colorado at least, also in the West, rocks which are popularly called " trachytes " are rhyolites or porphyries.

BASALTS and some of the other extrusive volcanic rocks assume a columnar form on cooling. Also, on the surface of the flow, the lava becomes minutely honey-combed like sponge, from escape of steam. This is called scoria and when these holes are filled with almond-shaped white crystals, amygdaloid. At other times the rock is a voleanic breccia ; that is, angular blocks of lava, great or small, are cemented together by lava. This probably was caused when the lava was pouring out of the fissure slowly, some portions congealed and were broken up by the onward flow, and again involved in the molten mass without being remelted. Enormous masses of volcanic breccia cover the San Juan region. Sometimes, by steam, the lava is blown into dust and descending with water, is worked up into a volcanic sandstone known as volcanic '"tufa" or " tuff."

OBSIDIAN is vitrified lava or volcanic glass.

Chapter V. Prospector'S Mineralogy,

T cE

There are two classes of minerals in which the prospector is interested, one may be called the "earthy'"' minerals, such as quartz, calcspar, etc., associated with the precious ores; the other, the metallic minerals constituting the ores themselves.

Both of these he wants to know at sight, or to determine with the simplest appliances. Generally speaking, his eyesight, his pocket-knife, his ore re-gli iss and a little acid, will be all he needs, nor need he concern himself about a great number of minerals, if he only knows the commoner ones well. Theearthy minerals form the gangue or veinstone of the vein in which the precious ores are distributed,

Gangue Minerals,

Earthy

These are princ'pally quartz, calcite, or limespar, dolomite, fluorspar and baryta, all of which we have already described among rock- forming minerals. These crystals are nearly always to be found in the adjacent rock as elements of that rock, and their more sparry condition in the gangue of the vein is derived by solution from the enclosing country rock, Thus, a vein running through granite, will contain mainly quartz, though calcite and fluorspar may be associated with it in small quantities, A vein passing through limestone naturally carries calcite or limespar. Sometimes baryta is associated with the calcite, especially if near the limestone ore deposit there are porphyries

Baryta has been detected as an clement of some porphyries which are probably ore-bearing, and when prospecting, we have found baryta to be generally an indication of ore near by, whilst calcspar, or quartz, alone, may or may not be barren. The float, or loose surface indications of ore-deposits at Aspen is commonly made up of calespar and baryta.

FLUORSPAR in Colorado is generally confined to veins in the granitic rocks aud in some of the eruptive rocks. Its presence is a good sign of ore,

OXIDES OF IRON AND MANGANESE.—These, often mixed together, form a large element in the gangue matter co' a vein or ore deposit. Manganese can be recognized by its

dark black color. A beautiful rose-colored carbonate-otmaganese called RHODOCROSITE is occasionally met with, associated with quartz and metal in some veins. ie

CARBONATE-OF-COPPER is olten associated with this gangue matter. It is readily distinguished by its bright green or azure blue color. "Float" is commonly rusty with iron-oxide streaked with stains of coppercarbonate,

SPATHIC IRON OR IRON CAR- BONATE OR SIDERITE occurs here and there in the gangue of

PLATE XXXIII. fissure veins. It is very like

Spathic Iron, brown feldspar but heavier.

These few common minerals

cover nearly all that are generally met with as indications of, or in important connection with, ore deposits.

As a rule most of these minerals occur in a massive state rather than as individual crystals in a vein.

Metalliferous Minerals,

Through these gangues of various characters, the precious metals are distributed in long, narrow patches or strings, or in large crystalline masses, or in scattered crystals, or in decomposed masses. The gangue matter is generally in the majority in a vein, and the ore thinly, sparingly, and irregularly, distributed in it. When a vein is said to be ten or more feet wide, it is not to be supposed, that ten feet of solid ore is meant, but that this is the width of the gangue between walls. The ore body may be only a few inches wide, The streak or main body of ore called the "pay streak" hasa tendency to keep near one wail or the other, or at times to cross from wall to wall.

High And Low Grade Ores.

In gold veins, flakes or wires of "free" or "native" gold occur in the decomposed gangue; and sometimes in the pure undecomposed quartz, "native" silver is found in much the same way, but more as specimens than as continuous bodies. Isolated patches of rare, o1 valuable minerals, such as Ruby silver, Horn silver, Silver glance, etc., occur locally in parts of the vein, sometimes coating stalac-

ol

tites or crystals of a "vugh" or cavity lined with quartz or other crystals. An assay from such picked

' ' Oo specimens would give a very unfair aver- ili, Yin age of a mine or prospect & gh Sy

The bulk of the profits of a mine come from the commoner minerals such as galena, pyrite, or lead-carbonate, and from the average grade of the mine. In California rold mines, the average yield of gold per oe is $16. In Dakote $6. In the jive. PLATE XXXIV, lead mines of Leadville, $40 per ton is the — YP Silver. average, and the ores are mostly low grade. A few mines of extraordinary high grade may yield from $75 to $100 per ton, but these are exceptional, Quantity of ore, facility for milling, cost of freight, the size of the vein, and its facility for working and nearness to market give the offset.

Decomposed Minerals.

Sometimes the gangue matter contains a variety of decomposed ore in rich secondary combination intimately mixed through its mass and rarely discernible by the eye. Thus yellow mud from a mine may assay high, from the presence of invisible chlorides or sulphurets of silver, No accurate estimate of the value of a mine, or even of a piece of ore, can be found, without an assay or mill-run, The reason for such richness in decomposed surface products, is, that nature has been for ages leaching out, concentrating and combining in richer forms, the essence, so to speak, ol the vein,

GRAY COPPER (TETRAHEDRITE). Besides the ordinary galena and pyrites common in most mines, we sometimes find considerable bodies of gray copper in mines, or intermingled wit other ores, This is generally a rich silverbearing ore, running from 60 ounces to some thousands perton. It generally occurs massive, rarely showing its pyramidal "tetrahedrite "' crystals. In appearance it is not PLATE XXXV. unlike a freshly broken piece ot bronze. It is more common in fissure veins in granite and eruptive rocks than in limestone. In Halls Valley, Colorado, it is asso-

Gray Copper (Tertrahedrite.)

ciated with baryta in a vein in the gneiss. [t occurs in the Georgetown veins in granite. In the San Juan district it occurs also associated with baryta in the Bonanza mine ; and an ore not identical with it in composition, but very like it in appearance, called bismuthinite, consisting of bismuth, antimony, copper and silver, is characterist'c of that region and is rich in silver. Bzsmuthinzte has a more shiny tin-like appearance than gray copper, and the red color which bismuth gives to charcoal under the blowpipe readily distinguishes it from gray copper,

Local Variations In Value Of Ores.

There are locally in different mining districts considerable differences in the value of certain minerals and ores. In one district gray copper may rarely exceed 60 ounces of silver, in another it is invariably over 100 ounces.

A coarse galena is generally poor in silver, while fine grained "steel galena" is generally rich in silver, but the reverse may also be the case. In some of the mines at Aspen, fine grained galena, especially near the surface, is quite poor in silver, while in other mines in the same district it is exceedingly rich. Localities occur also where coarse-grained galena runs well in silver and is richer than fine-grained galena. This is the case at the Colonel Sellers mine at Leadville. So one mining district or even one mine is not a rule for another.

PyYRITES.—Iron pyrites and copper pyrites, common in most of our quartz veins in granite and in the eruptive rocks, may yield both gold and silver, but usually the former, There are certain districts more characterized by pyrites than others, such as the Central City district. These are generally gold-producing districts. Some of the mines at Breckenridge and South Park have strong pyritiferous veins in eruptive dykes, such as the Jumbo mine. These have of late produced a great deal of gold. The same district, however, produces large argentiferous lead veins. Pyrites generally favor the granite, eruptive and crystallized rocks. The quartzites of the Lower Silurian of South Park and Red Cliff are often pyritiferous and generally gold-bearing. In limestone the pyrites is rare or absent, its place being filled by some form of iron oxide. In the deeper mines of Leadville, however, this iron oxide is beginning to pass down into the iron sulphide or pyrite from which it was derived, Iron pyrites can generally be distingy.ished from

copper pyrites by its paler, more brassy color, ey its superior hardness and by its crystallizing in cubes. Copper pyrites is much yellower and' softer, and crystallizes i" a more pyramidal form, A vein may glitter with showy pyrites and yet be quite valueless. It 'usually yields more gold in its decomposed, oxidized condition than in its unaltered state. In the one case the gold is free-milling, and in the other it must be smelted at much greater expense.

SULPHURETS.—This term amongst miners is loosely used, and often means some decomposed ore whose ingredients cannot be determined at sight, but which somehow assays high in silver. True sg a ta or sulphide of silver is a name embracing a large family of rich silver ores, among which are stephanite or brittle silver, argentite or silver glance, sylvanite or graphic tellurium, and polybasite.

All these rich ores are compounds of sulphur and silver and other ingredients in varying proportions, They are somewhat alike in appearance and not always so easy to distinguish.

ARGENTITE, silver glance, or sulphuret of silver, is of a blackish, lead-gray color, easily cut with a knife, and consists of an aggregate of minute crystals. Its composition in 100 parts, is sulphur 12.9, silver 87.1. Under the blow- pee it gives off an odor of sulphur, and yields a globule of silvet

STEPHANITE, or "brittle" or "black" silver, is closely allied to argentite. Its composition is sulphur, antimony and silver, silver being 4 68.5 per cent. The crystals are small, VIN Under the blow-pipe it gives off garlic fo fumes of antimony and yields a dark globule from which, by adding soda, we get pure silver,

POLYBASITE, Common at Georgetown and in some of the Aspen mines, such as ) the Regent or J. C. Johnson, on Smuggler Hill, is like the others, but of a more flaky, scaly and graphitic appearance. It Bs a is not unlike very fine-grained galena, PLATE XXXVI. yielding 150 to 400 ounces of silver per Stephanite. ton.

These sulphurets sometimes line little cavities in limestones with a dark sooty substance, which under the microscope proves to be crystals of one of the sulphurets of silver. Sometimes also a rock is stained all through a blackish gray by these sulphurets. [ron or manganese may

produce much the same effect, but an assay will soon reveal the difference. Associated with such a rock we may see flakes or wires of native silver that have emerged from the

sulphide state. CHLORIDES.

CHLORIDE OF SILVER (" Horn silver," or Cerargyrite).— This is another result of secondary decomposition from a sulphide state (silver sulphide), It isa greenish or yellowish mineral, like wax, and easily cut with a knife. It is a very rich ore running 75.3 per cent. silver, the renvainder being

chlorine. As a secondary product of decomposition it is. generally found near the surface or in cavities, sometimes.

deposited on calcite or other crystals. In the mines at Leadville it is commonly associated with other decomposed ores, such as carbonates. In the Chrysolite mine, a mass weighing several hundred pounds was found. Chloride, bromide and iodide of silver are closely related, being compounds of chlorine, bromine, iodine and silver. It is noticeable that these salts are the elements of sea water, and that these ores are often found in marine limestones. According to Mr. Emmons, the change at Leadville from sulphide

to chloride was produced by surface waters; these waters.

are found to contain chlorine, which they probably derived from passing through the dolomitic limestones which contain chlorine in their crystals, and these limestones perhaps originally derived it from the sea water in which they were deposited. Chloride of silver is found at Aspen ar' abundantly in the outcrop of mines in New and Old Mexico,

Sulpharsenites.

Ruby SILVER (Pyrargyrite and Proustite)—Composed of sulphur 17.7, antimony 22.5, silver 59.8— 100. Crystallizes in rhombohedrons, is seen in spots or crystals on a mass of ore of a deep red or blackish tint. When scratched with a knife it shows a bright or deep red color. In some mines this very rich ore occurs only as specimens, but in others it is present in sufficient quantity to largely influence the value of the ore in bulk. In parts of the Granite Mountain Mine in Montana, it constitutes the principal ore, associated, however, with other mineral. It there occurs in large masses and accounts for the extraordinary richness of that celebrated mine, Proustite is much the same, only lighter red, and consists of sulphur 19.4, arsenic 15.1, silver 65.5 100,

a

Carbonates.

This term also embraces a large family, the commonest being carbonate of lead, (cerussite) and carbonate of copper, (malachite and azurite).

COPPER CARBONATE can never be mistaken, owing to its brilliant green and azure blue color. Co per stains are among the common surface signs of a 'lead.' It is generally associated also with rusty stains. Both are the surface products from copper and iron pyrites forming a vein below ground which may or may not be profitable. Copper stains are common enough in many rocks, but do not always lead to bodies of ore. In South Park the red Triassic sandstones are so stained, but yield no ore. Along our foothills there is quite a stained belt from Golden to Morrison and through Bergen Park. But few promising deposits of copper or other ores have been found, although handsome specimens of native copper have been discovered near Golden.

At the Malachite Mine on Bear Creek, near Morrison, a prospect was at one time opened showing a good deal of silicate of copper (chrysocolla) and malachite, but for some reason it has not been worked since.

CopPER in its native or uncombined state is rare in Colorado, and so far, we have as yet no true profitable mine. A great deal of copper is found associated with other ores, and is extracted by some of the smelters. Carbonate of copper is commonest in the limestone districts, as might be expected from the carbonating influence of limestone upon minerals in it, or mineral solutions passing through it. Carbonate of iron (spathic iron, or siderite), constitutes part of the gangue matter in some of our veins, and may also be found associated with coal seams generally, in the latter case in an oxidized condition,

CERUSSITE (Carbonate of lead). This is mostly found in the limestone districts such as Leadville. It isthere known in two forms, one called " hard carbonates," the other " soft" or "sand carbonates." The crystals of this ore are small prisms, sometimes combined into a cross shape, of a pale grayish white, and might be taken for some form of carbonate of lime or gypsum, their weight, however, soon shows the difference. They are a secondary product of decomposition consisting of carbon dioxide and lead oxide; as a carbonate they effervesce in nitric acid, and yield lead when heated. Cerussite is exceedingly rich in lead, carrying 75 per cent. The white lead of commerce has the same composition, In Leadville and elsewhere in Colorado it is

silver-bearing also, and though low in silver, the facility of its treatment at the smelter makes it a very desirable ore, As a rule it contains less silver than the unaltered galena, but is more easily treated than the latter. The process of change or derivation from asulphide state (¢. e., from galena) to a carbonate, is well shown sometimes in a piece of Leadville ore. A central cube of galena is surrounded by a grayish green ring of sulphide of lead or anglesite, and outside this

Plate Xxxvi.

Simple and Compound Crystals of Carbonate of Lead (Cerussite.)

may again occur crystals of lead carbonate. Thus the proess is froma sulphide to a sulphate, then to a carbonate. The so-called "hard carbonates" is a brown mass consisting of a hard flinty combination of iron oxide and silica, impreg-

nated with crystals of lead carbonate, with which are often silver chlorides, also. The "sand carbonates" result from the decomposition and kre: iking up of the hard carbonates,

or from a mass of pure crystals of carbonate of lead, w hich are, by nature, loose and incoherent. The Leadville mines are getting below these products of decomposition and entering upon the original sulphides of galena and iron, 'The yield, however, is said to be equally good.

ZINC-BLENDE (SPHALERITE), " BLACK JACK." Common in most mines mixed with other ores. As it isa very refractory mineral in smelting, much of it is not desirable in a mine. It is easily recognized by its brown resinous look, or when very black by its pearly luster. At Georgetown, near the surface, brown rosin-zinc-blende" carries silver, and is associated with rich ores, such as polybasite and gray copper. With depth the zinc-blende becomes more abundant and blacker, and loses much of its silver properties. Zinc-blende may run from PLATE XXXVIILI. nothing, to twenty dollars silver, and Zinc Sulphide

rarely as high as $100 per ton, (Zine Blende.)

In some mines in the San Juan it occurs abundantly near

the surface and fades out with depth. We have no true zinc mines in Colorado, the zinc being mixed with other ores, In some mines in Pitkin County the zinc predominates over all other ores, and though it runs high in silver the smelters do not care to take it, on account of its refractory character. In the Eastern States where zinc smelting is. a specialty, such ore might be separated and both silver and' zinc saved. In Missouri zinc and lead are found together.

In Colorado there are no mines of one mineral alone, as: in some other parts of the world. We have no true lead,. zinc or copper mines; these baser metals are either argentiferous or auriferous, and their baser qualities are sacrificed! for their richer ones.

CHAPTER VI. ORE DEPOSITS. THEORIES REGARDING THE ORIGIN OF ORE DEPOSITS,

A prospector will find both a practical as well as scientific interest in considering the origin of ore deposits. Where do the precious metals come from? What is their origin ? Hiow are mineral veins formed and how do precious metals: get into them ?

The remote origin of metals is a matter of speculation. They may have formed part of that gaseous mist from which, according to the nebular theory our planetary system was evolved. As this passed into molten condition the metallic vapors may have separated into various combinations and consolidated and been arranged in the general make up of the world according to their specific gravity. Some have thought that the interior of the earth may be more metalliferous than the surface crust since the earth grows heavier: toward the center. Volcanic rocks coming up from depths: unknown contain a large per cent. of the heavier metals, particularly iron. But we turn from these speculations to. theories of more practical interest to the prospector.

A prevalent theory amongst miners and prospectors is. what may be called "the igneous theory " or the fiery origin of veins and metals, They are apt to attribute the fissures: themselves to some violent volcanic outburst, and consider

the quartz gangue or veinstone, together with the metals, as molten volcanic emanations filling at onetime a wide gaping fissure. a

Others demand an intense heat considering that the metals in the veins were reduced in the bowels of the earth by intense heat to a vaporous condition, which, ascending through the fissures, condensed and consviidated in a crystalline form in the upper and cooler portions of the fissures, as certain sublimed mineral vapors from a smelting furnace sometimes collect and recrystallize in the flues.

By many prospectors every indication or surlace appearance of a vein, or even a likely-looking rock, is called "a blow out," a term suggestive, at least, of some sort of vol-

Plate Xxxix,

Fold Passing into Fault Showing Broken Character of Fault Fissure and Adjacent Rocks Producing Later a Brecciated Vein and '' Horses,"'

canic explosion at that point. With them, the " fire and brimstone" origin of ore deposits is as deep seated as the veins in the rocks,

These ideas contain a measure of truth, and were naturally suggested by observing that our ore deposits are so generally associated with volcanic rocks aud evidences of past heat ; and it cannot be denied but that the presence of these volcanic rocks had more or less to do with the ore deposits.

The modern study of ore deposits inclines to the belief that we need not draw directly upon the unknown profound supposed ignited regions of the earth's interior for the direct source of metals found in the veins, nor entirely from violent explosive volcanic agencies, nor from very intense heat, but

j

aplmncar lanham erro

rather that we may look nearer home for the immediate source of both metals and veinstone, namely, in the elements of the common country rock adjacent to the ore deposits ; and for the medium of distribution and concentration of ore and veinstone from nothing more violent or volcanic than water, more or less heated and alkaline. Nor is it so absolutely necessary to suppose that the filling of a vein fissure with quartz or metal must needs come wp from profound depths, and from a foreign source; but quite as likely from the adja- PLATE XL.

cent sides of the fissure, A Tight Fault Crevice Being Attacked by or even from above the Solutions Producing Finally a Narrow Fisposition later occupied by sure Vein—Small Dois=Ore Solutions. ore.

Veins of whatever kind are not vents for molten volcanic matter, but simply courses for water, more or less heated and alkaline, in fact, channels of mineral hot springs carrying earthy minerals and metals in the same solution, and depositing them, partly by cooling and sometimes by chemical precipitation and mainly by relief of pressure in such openings or weak places, as may be found convenient.

The origin of these openings and weak places in the earth's crust is various. The class of great fissures holding "fissure veins," cleaving Our mountains from top to bottom to an unknown great depth, were caused by the fracturing and faulting of rocks, in the gradual process of fold-

PLATE XLI. ing upwards, and elevation

Gash Vein Fissures in Jointed Eruptive of the mountain system, a Sheet' process so slow and grad-

ual that it may be even

progressing now without one noticing it. The relief of

peremrernenccmress very

'hough the fault fissure vy extend to very great it was probably not vioje.? but gradual, From time to time, the shock produced by the grinding together of the walls of a fisseve ina slip or jerk of only afew inches, may have given rise to severe earthquakes on the surface.

A great fault fissure, too, was likely to be accompanied by minor adjacent faults and also by small

iat TH ie, Nu

Plate Xliii.

Jointed Granite.

treme tension from folding results finally in faulting;

Plate Xlii.

Joints and Bedding Planes.

incipient fissures or loose fractures of the rocks, producing parallel fissures and zones of fissure veins. Other openings,

occupied now by fissure veins, may be compared to those joints common to all rocks, the result of contraction and shrinkage of the granitic or volcanic rocks from a soft, semi-plastic condition to one more solid and compact. But in no case we think were the fissures now occupied by veins 50 to oo feet wide originally wide open chasms like that which swallowed up Korah, Dathan and Abiram in Bible history, but rather cracks fit-

ting very tightly together by enormous lateral pressure

such as we see in fault cracks of the present day not yet occupied by veinstone or gangue or metal matter. These narrow cracks were worked upon by alkaline and acid solutions and enlarged by the process, the rock gradually eaten into being replaced by gangue and metal matter, a process often further assisted by the shattered character of the rock commonly found

Plate Xliv.

Jointed Slate.

adjacent toa great fault; this shattered cavity was sooner

VHRR mallet Nae pagal ic Va Nadens AVEC HEPELN

or later eaten out, so to speak, and replaced by mineral matter, Some of the broken rock being not consumed in this way, was left, forming fragments in the vein which when small are called " breccia" and when large "horses." The great "gash" fissure such as we find occupied by sc. call.' fissure veins in volcanic siee!. such as those of the Sa: 'ua.. region, Colorado, appear bs due not so much to great car') movements like the last, as to openings formed by cooling and -traction of the lava, somewhat iiay be observed Sos ae SERRE

ne eee " PLATE XLV. on the cooling of iron in a slag furnace. Ore deposits of lead and other minerals forming bedded deposits in limestones find their way in solution through the vertical joints common to all water formed rocks, resulting fromgy contraction in consolidating froma soft, muddy condition. Such fissures are short but they act as channels toa more important line of weakness occupied by the main body of the blanket ore deposits, viz. the dividing line be-

Joints in Columnar Basalt,

PLATE XLVI. tween one stratum Contact Ore Deposits Between Porphyry und and another. An- Limestone. other line of weak-

ness for the attack of mineral solutions is at the juncture of a porphyry sheet or dyke with some other rock, The interval between them is often occupied by a "contact vein." The heat of the volcanic matter together with steam may have influenced the solutions, even if the porphyry did not actually supply the metallic element in the vein.

Folding And Faulting.

In the many and great upheavals of the earth's crust, resulting in continents rising above the sea, and on those

continents still greater and sharper upheavals forming mountain ranges, rocks have been much broken and fractured, from great fractures, forming fissures miles in length and depth, down to little cracks of but a few inches. Much of this fracturing has been caused by the folding and crumpling upwards of strata into mountains, accompanied by great crushing and mashing together of the rocks. When this lateral tangential folding and compression of the rocks reaches its maximum intensity, the rocks break, and a fault or slip is the result, with its attendant fault-fissure. This relieves the strain for a while, but the shock, doubtless at the time accompanied by earthquakes on the surface, resulted in a general breaking up of the adjacent country into many parallel and smaller faults and cross faults, besides a general shattering of the ground intermediate to the faults. A region thus faulted and shattered is just in the desired condition for forming a future mineral belt or mining region, when the cracks and scars thus made have been healed and filled up by mineral matter, brought in through the agency of watery solutions more or less alkaline or heated. INTRUSIVE IGNEOUS ROCKS,

When these fault fissures descend toa very great depth, they may tap the molten rock reservoir supposed to lie bereath great mountain ranges, and the molten lava or porphyry, rushes upward through the weak line of the fissure, fills it with its matter, which on cooling becomes a dyke instead of a mineral vein, These eruptive rocks may or may not reach quite to the surface and overflow it in a lava sheet. If they do not, they find relief by intruding themselves laterally between the layers of stratified rocks, whose leaves or bedding planes may have been partially opened, like the leaves of a crumpled book by previous action of folding. In such cases the porphyry dyke or intrusive sheet may, if it be mineralized, answer all intents and purpose of a mineral vein, or the ore may be found on one or both sides of such a sheet, in the line of separation and weakness between it and the adjacent strata, or it may permeate and mineralize by a "substitution" process an adjacent porous or soluble rock such as limestone. Thus both in the dyke or intrusive sheet itself as well as at its contact with other rocks, the prospector should look for signs of precious metal.

If the dyke or sheet should be decomposed, clayey and

rusty, it may contain free gold disseminated through it, which, at a deoth which may or may not be ever reached by mining, passes into the auriferous iron-pyrites from which the free gold originally came. In this case the ore will be no longer "free" or " free-milling," but of a character that must be subjected to the more expensive treatment of roasting or smelting. Little stringers or veinlets of quartz, if observed in such an eruptive rock should be carefully examined as the most likely source of the richest gold ore, Some of our most noted gold mines in the West are ir these "rotten" mineralized dykes or eruptive intrusive sheets. "Likely signs' in such would be rusty 'gossan" stains of green carbonate of copper and gouge or clay matter. It is worth observing that the dyke may be only valuable as a mine as far down as the decomposition lasts and as long as the ore continues in a free state. With depth, the pyrites of the undecomposed lower portion of the dyke may be found too poor in gold to pay tor smelting even.

As this desirable state of decomposition is the result mainly of the action of surface waters, a prospector may consider sometimes, where, on the outcrop of such a dyke, the rock is most likely to be deepest affected by surface action; for example, more probably below the ofd stream bed than on the top of a mountain, but this is not always the case. Most dykes and intrusive sheets when mineralized, are mineralized by pyrites, rather than by galena, hence they are generally more gold-bearing than silver-bearing. The contact deposits adjacent to a volcanic rock, may have been aided in their deposition by steam issuing from the molten mass, or by heated waters or steam ascending with it, or generally by the heat of the dyke, as heat together with moisture is a great solvent of rocks and promoter of chemical action.

In granitic rocks, if a "contact" deposit occurs adjacent toa porphyry dyke, it is usually a quartz vein, or a vein composed of quartz and feldspar, commonly called " pegmatite."" Such contact fissure veins may be on one or both sides of a dyke. The Telluride veins of Boulder and the gold and silver veins of Idaho Springs, Central and Georgetown in Colorado are often so situated,

CONTACT DEPOSITs,

When a porphyry sheet intrudes itself into limestone as at Leadville, the ore may be looked for on either side of this

sheet ; but more commonly below it, At first the ore seems to permeate the limestone immediately at the line of contact, but from this somewhat horizontal line, it is apt to run down through joint cracks in the limestone, enlarging the cracks by solution, and substituting or replacing the dissolved rock with silver-lead ore, by a process callec " metasomatic substitution,"

Plate Xlvii.

Contact Blanket '' Ore Deposits and Contact Fissure Veins."'

' Metasomatic' means literally "an interchange between one body and another." In this case it is an interchange between metal and limestone, by which the limestone is gradually replaced, molecule by molecule, with metallic

matter, Thus we may suppose, that as the mineral solutions were working on the limestone, rotting and soaking and dissolving it, as each molecule of lime was dissolved, it was replaced or substituted by a molecule of metallic matter, until a large body of the rock was replaced by ore, This appears to be the true way in which most of our ore bodies were formed in limestone and other soluble rock, rather than that they were "washed in " and " deposited" in " preexisting large cavities "' as some have supposed,

Blanket Deposits On Bedding Planes,

The solutions having worked their way down through these vertical joints, may reach a second fine of weakness, viz., the bedding plane or line of stratification between one bed or stratum of rock and another, and deposit along it as on a floor, This may be between one heavy bed of limestone and another. If it is between two déssimzlar rocks, such as between limestone and quartzite, or even between limestone and magnesian limestone called dolomite, it comes under the name of a "contact deposit. Thus it is noticeable that besides great fissures, lines of weakness or " bedding planes" are favorite places for ore deposits, to which the natural vertical joints often act as feeders, as well as themselves containing large " pockets"' or "chambers " of ore. When the deposits are confined to these " pockets " and there appears to be no " blanket" deposit, the mine is said to be " pockety," and after a " pocket " is exhausted an immense amount of money and work and blind " gophering " often follows in hunting for another pocket. There is in this case little rule to guide the prospector, Locally, by experience in the mine, he may notice that some fine line of gypsum, calcspar, or iron stain is apt to lead toa pocket and follow it. In the mines of Aspen, where the mineral zone lies irregularly but generally near about the line where the limestone becomes dolomised, a miner, when his ore " plays out," follows as closely as he can this line, which he is able to do by the different hardness of the limestone and dolomite, the latter causing his pick to 'ring.' In every mine there is generally some local sign to assist the miner in following up his lost ore.

Surface Sicns,

The pres ector in hunting on the surface outcrop for signs of such contact or blanket or pocket deposits must

bed

look out for signs of decomposition along the line of contact, such as lead carbonates, carbonate of conyers oxide of iron, together with crystalline matter such as calcspar, gypsum, or baryta. He may also observe in the vertical joints leading down from the surface into the body of the limestone, rusty clay fillings and iron stains. In_ these "blanket," bedded deposits, prospects on a large scale may

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PLATE ALVIII. Prospecting with Diamond Drills.

sometimes advantageously be done by drilling with diamond drills from the surface down through as many of the strata us are suspected of being ore bearing, the "cores" brought up will show if an ore body has been penetrated together with its approximate thickness at a certain point, and if this process is continued over a certain area, the approximate areal limit of the ore body may be ascertained. This work may follow upon a close examination first of mineral signs along the outcrop, Itis sometimes done after an area has been exploited for some time by actual mining with a view of discovering new bodies or continuations of the ore.

True Fissure Veins,

Whilst profound fault cracks may be filled by lava, those not descending to such great depths doubtless lay open, till they were gradually filled by solutions carrying in earthy vein-stone and metallic matter; in a word they were the channels of mineral or hot springs. It must not be supposed that these fault cracks were ever " open chasms " commensurate in width with the wide dykes and veins now found in

Plate Xlix,

Brecciated Lode with Quartz Geodes.

them, but rather in some cases very Close fitting cracks, mere lines of weakness, the walls appressed closely together by prodigious lateral pressure. In other cases the fissure would be rather a shattered zone passing down through the strata, than one definite line of fissure. Doubtless when the molten lava ascended through these fissures it greatly widened them to admit of its volume. In the case of true fissure veins, the fissure or shattered zone was enlarged by the corroding, substituting power of

acid mineral solutions till we have to-day a fissure vein twenty to fifty or more feet in width, In the shattered zone, this substituting process would go on easily and rapidly,

Plate L.,

Brecciated Vein,

until nearly all the shattered fragments were replaced by mineral matter except a few " indigestible " pieces, which if

'small, would cause what is called a brecciated vein, and if large, " horses' in a vein, These fragments are not so much pieces that have fallen from above into an open fissure gradually filling up with solutions of quartz and vein matter in which they became entangled, but rather undigested, iunsubstituted fragments of the wall rock, immediately adjacent to the fragments, for at times some line in the fragment corresponds to a line in the adjacent wall rock without evidence of any serious displacement. Again, the 'shadowy outlines of fragments can be observed partially but not entirely replaced by quartz or vein matter. Sometimes the " breccias' are surrounded by rings of quartz or metal and called " cockade ores."

Horses,

In the San Juan region in Colorado, Where we have won-

derful opportunities of observ-

1 ing extensive sections of great

fissure veins descending the faces of cliffson either side of a canyon for two or three thousand feet, such broad veins at intervals split up into two or three arms enclosing large fragments or "horses" oi the lava country rock, and again unite to form the main vein. These veins occupy a once shattered fissure, the walls of which were originally neither straight nor regular, bt shattered and cracked. The vein matter insinuated itsel! between the shattered portions, sometimes forniing a breccia" of small fragments, at others PLATE LI. "horses " of large ones.

Horse or Rider, The appearance of these great

San Juan veins from a little dis-

tance is that of broad yellow stains of oxide of iron contrasted with the sombre gray of the lava rocks. In some pan in this region the quartz, by reason of its superior 1ardness, stands up above the softer lava like a low, rusty, or white wall. Again, at other localities instead of being a bold outcrop, the vein is represented by a sharp, shallow

/ j

ff

depression forming a narrow little ravine or trench, the path of a rivulet and zone of abundant vegetation. In this case the vein was full of dec omposable minerals, such as pyrite whose oxidation dec omposition products were washed out leaving a depression in the rocks,

So, amongst some of the indications of a fissure vein to the prospector we may note:

ist. Brown or green stains on rocks,

2d. A bold quartz vein like a wall above the country.

3d. A narrow ravine or gulch.

4th. The path of a sone and exuberant growth of vegetation,

Signs Of Faulting,

As these fissure veins are generally the filling of fault cracks, and the fissures are mainly due to faulting, a prospector should be able to recognize the surface and othe signs of faulting.

Faulting as we have said, is generally the result of extreme folding. So, in entering a mountain region by way perhaps of a canyon, cutting right through it on the exposed face of the cliffs, he m: ay Observe some of these folds or arches, low and gentle at first, but gradually, as the range is penetrated further, increasing in sharpness, steepness and closeness ; with this increase we may expect faults. The presence of the fault may be indicated by a little " sag' or depression in the outline of the hill, or by a line of rubbish and broken rock descending the face of the cliff, or by a zone of exuberant vegetation, or by the pathway of a little rivulet. He will observe a general fractured tendency of the rocks as they approach the fault line. By closer search he may notice pieces of rock polished or slickensided by the movement of the walls of the fault slipping and grinding upon one another. Slickenside is a sure proof of motion having taken place in the rocks, and is often observed on the walls of fissure veins. A much faulted region is often marked by a step-like out- PLATE LII. line, each step represent- Vein a Faulted by Cross-Vein B. ing the fallen or risen side of a fault block. These fault lines should be carefully examined for mineral indications, especiaily if the fault line is

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occupied by a porphyry dyke ora vein of quartz or calespar, Sometimes these fault lines are totally barren, both of quartz, veinstone or metalliferous matter, They may be filled up with clay, rubbish and broken rock, or the two walls may be actually welded together by pressure accompanied by a certain amount of heat, producing local metamorphic action,

Faulting too in some regions may have occurred comparatively recently, or at least after the period most marked by deposit of mineral solutions and ore deposits, in which case the fissures may be barren or at present occupied by hot or mineral springs making veins for the tuture, A stupendous, comparatively modern fault, runs along the west base of the Wahsatch mountains in Utah, its line is marked by a series of hot springs.

Along the face of a canyon wall the prospector may notice some peculiar stratum near the top of the cliff and its counterpart out of place near the bottom, showing that a fault has occurred, whose amount of slip he can easily estimate measure; but when a fault of many thousands of feet occurs, a knowledge of the different geological periods involved in the slip is necessary to estimate the amount of fall, Thus if

ol

; 81

a prospector by his geological knowledge should recognize a Cretaceous rock brought up in close juxtaposition to a Silurian rock he would know that a stupendous fault had occurred at that place, involving the entire thickness of the rocks composing the periods intervening between the Silurian and the Cretaceous,

That a faulted region is one in which great folding due to lateral tangential pressure has taken place, the folds eventually breaking down in faults, is well seen in the structure of the Mosquito Range in South Park, Colorado, which embraces the Leadville mining district,

The comparatively horizontal strata of the Park as they approach the Mesquito Range begin to fold gently, the folds gradually increasing in steepness and closeness as they approach the axis of the range. As we pass up Four Mile Canyon, which shows a complete cross section of the range, we find the axis to be formed by a magnificent and very steep arch, well shown on the face of Sheep Mountain, which having arrived at its utmost tension breaks down in what is called the London mine fault, traversiag and split ting the range for twenty miles. The line of the fault is

shown by a depression between Sheep and Lamb Mountain

In nearly every canyon along the Sank of fois range, the line of the fault is easily traced by sinus: arches and "sags "and by a peculiar wavy loo. ot the turfed strata as they bend ie toward the fault, + we penetrate further across the range, we pass a series of such faults, each one formerly represents by a steep fos that preceded the faulting, Henee it) that we descend from the top of this range down into adville and the Arkansas Valley by a series of gigantic steps or benches, each bench representing a fallen faulted block, Faults have their points of maximum depth and disturbance, from which they are apt to die out at either endin folds or rounded hills. (reat faults are accom paid by minor paralleland cross faults

The ultimate cause of this folding and faulting is ottributed by some geologists to the interior of the earth growing colder and contracting, Causing the surlace crust to shrink and fold in adapting itselfto the shrinking interior, Professor J. F. Kemp says: "The strains induced by cooling and contraction of the earth are the most importasit cause of fracture. The contraction develops a tangential strain which is resisted oy the arch-like disposition of the crust, Where there ts insufficient support, gravity Causes a sigging of the material into troughs or synelinal folds which

— apap ater Wea ED EAP PEMA gO ET EE A EINE RIB LEVERS HSA EME TR ORT RC oor

$2 leave corresponding arches or anticlinal folds between them. Where the tangential strain is greater than the ability of the rocks to resist, they are upset and crumpled into folds from the thrust, Both kinds of folds are fruitful causes of fissuring cracks and general shattering, and every slip from yielding sends its oscillations abroad, which cause breaks along all lines of weakness."

Joints,

Joints, common to all rocks, appear to be due not so much to faulting and motion, as to shrinkage of the rocks in passing from a soft matter or muddy condition to one of consolidation, A good many so-called fissure veins, even in the granite series, appear to occupy extensive joint cracks, rather than fault planes. These may be due to the general shrinkage of the whole mountain mass in Consolidating from a sem:-plastic or aqueo-igneous state of softening to one more consolidated and rigid,

The joints in lava sheets forming curious columns like those of the Palisades of the Hlud) on are due to the same shrinkage trom a molten state. Such joints may sometimes be mineralized for a short depth, forming what are called "sash" veins, rather than true fissure veins, The joints in sedimentary rocks are due to consolidation from a soft, muddy, incoherent condition; such joints may similarly be occupied by gash veins, or may lead to pockets or wide blanket deposits.

The line of weakness between one stratum or one set ot strata and another, often a favorite line for blanket deposits, is due to one stratum being first laid down and partially consolidated before the next was laid later on top of it.

Impregnations,

Rocks made up of joose material such as porous sandstones and conglomerates are some.imes permeated by ore solutions, as for example, the "Silver-reef sandstone ot Utah. Sandstones are frequently impregnated with iron and copper stains, In fact, if we consider that cre bodies were Geposited from aqueous solutions, we have only to consider the various opportunities the rocks afford by their texture, structive, etc., for this process, Veins, ina word, are filled waterways of many and various kinds,

Chapter Vii.

Various Forms Of Ore-Deposits Ore Beds,

"Ore beds are metalliferous deposits interstratitied between sedimentary rocks of all geological ages. They lie parallel to the planes of stratification and follow all the contortions of the enclosing strata, hence they are thrown into folds, troughs, arches, saddles, or basins. The upper portions of the arches may often have been removed by erosion, or the strata may be faulted." The ore deposits or beds at Aspen occupy a taulted syneclinal told or basin, The enclosing rock is limestone, in part dolomitic. At Leadville the deposits OCCUPY part ot

Fault

Ravine

Ore

An al

A series of faulted anti-

clinal arches and syn-

PLATE LIV. clinal troughs, of which

Faulted Ore-Beds in Anticlinal and Synelinal the Mosquito range is Folds, the mainaxis. The beds

lie between dolomitt limestone and sheets of porphyry. The ore beds partake ot all the folding, faulting and other contortions which the enclosing rocks have suffered in the upheaval of the mountains.

The thickness of such deposits varies much and may gradually thin out and disappear, but may also continue long enough tor all mining purposes.

Often there are no sharp limits between an ore bed and the enclosing rocks, or between the ore bed and the walls, if walls exist at all. The ore appears to impregnate the surrounding rock by a chemical interchange between the elements of the rock and the ore. Such a' metasomatic " interchange, "substitution," or "replacement" appears to have taken place in the argentiterous lead deposits of Leadville and Aspen between the ore and the limestones.

According to Phillips, 'a true ore bed never produces a 'combed' or 'ribbon" structure made up of symmetrical

layers, such as is common in so-called 'true fissure veins, and is usually without the crystalline texture observable in

veinstones,"' UNSTRATIFIED DEPOSITS, FISSURE VEINS, ETC,

Mineral veins are changeable in character, and their appearances of a perplexing and complicated nature. There is a gradual passage from one form to another, so that it is difficult to classify them. There is often no such sharp distinction between one form of ore deposit and another, as legal disputes would sometimes demand, and a witness should hardly be called upon to assert on oath that such a vein is a "true fissure," or another a "bedded vein," ora third a "segregated vein." " Nature abhors straight lines " and sharp distinctions, and delights in blending one form imperceptibly with another,

Phillips divides veins into two classes, " regular and irregular veins." " Regular unstratified deposits include true veins, segregated veins and gash veins, Irregular deposits include impregnations, fahlbands, contact and chamber deposits."

Veins are collections of mineral matter, often closely related to, but differing more or less in character from the enclosing country rock, usually in fissures formed in those rocks after the rocks had more or less consolidated.

All veins do not carry metals; sore are merely barren quartz, feldspar, or calespar, like the barren veins we so often see traversing granite or limestone PLATE. LV: rocks, oe A Split Vein,

Veins may divide, " split up or thin out, and are irregular in shape and structure, owing to the irregular width of the fissures and to other causes.

Definition Of Mining Terms,

The rock in which a vein is found is called the "countrv rock,' e. ¢., limestone, granite, porphyry. The portions of country rock in direct contact with the vein are called respectively the "hanging wall," or roof, and the "foot wall" or floor. This is onlv in inclined or flat veins, as a vertical fissure vein can have neither roof

nor floor, but only two walls, east and west, or north and south, according to the compass. The inclination of a vein to the horizon is its "dip." The horizontal direction of a vein at right angles to its dip is its "strike." The latter may commonly be observed along the surface outcrop, the former either in the workings of the mine or where the vein is exposed on the side of a canyon,

Both dip and strike of a vein often vary much, the former with depth, the latter with extension across the country. A vein or ore deposit will not unfrequently begin with a gentle dip, and increase rapidly in steepness with depth. The ore deposits on Aspen Mountain commonly begin with a dip of 25°, and at a depth of less than a thousand feet reach 60° or more,

As fissure veins commonly occupy fault fissures, their irregularities in dip and strike correspond to those we have already spoken about, under faults,

The angle of dip is usually taken from its variation from a horizontal, not a perpendicular line. Thus a dip of 75° means one that is very steep, while one of to' is a gentle inclination,

A laver or shee' of clay called " gouge," or selvage, often lines one or both walls of a vein between the country rock and the gangue or vein proper, It is derived from the elements of the adjacent country rock, decomposed by water, and sometimes by the friction of the walls of the fissure against one another, or against the vein matter, in the process of slipping and faulting, which is often shown by its being smoothed, "slickensided," polished or grooved. Gouge often contains some rich decomposed mineral in it, such as sulphurets of silver. It sometimes occurs in the heart of a vein, especially if that vein has been re-opened anew by movements of the strata. The "Chinese Tallow" gouge of Leadville results from the decomposition of the feldspars in the adjacent white porphyry, and is a hydrous silicate of alumina.

In the granite veins in Clear Creek County the gouge is derived from the teldspars of the granite. Gouge is sometimes useful in defining the limit of the vein between walls, thus preventing unprofitable exploration into the "country," It is also a guide for following down a vein when mineral and gangue may be wanting or obscure.

Both walls are not always clearly defined by slickensided surfaces, by gouge or other mark, and so at times the vein is lost.

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False walls, caused by movements in the adjacent strata, by joints, etc., also mislead,

"It is not uncommon for a fissure vein to have but one clearly defined wall, the other, if it exists, being obscured or changed by mineral solutions. Sometimes two cracks or fissures occur parallel to each other and the intervening country rock has been altered and mineralized into a vein, It is probably in this way that many wide veins were formed.

Mr. Emmons has found that fissures are formed by great movements of the earth's crust or by local contraction of the rocks, and that a fissure is not necessarily one with well defined walls at considerable distances apart, filled after the formation of the fissure, but that the ordinary cracks or joints in granite quarries, extending regularly to great lengths or depths, illustrate the original fissures which have been changed by yercolating waters carrying mineral soutions into veins and deposits of ore, In all crystaline and sedimentary rocks, these cracks or joints run parallel to each other at various distances apart, PLATE LVI. often plentiful and close together, In cases where percolating waters were charged with the proper metals and veinstone matter and the necessary chemical and physical conditions existed, the rocks lying between those cracks or joints were altered into ore,

As one element was dissolved another took its place, so, according to this authority, it would seem that even a fissure vein may be only a sort of "metasomatic replacement " of rock by mineral, Hence what is commonly accepted as a "wall" of a vein, is not necessarily one, and cross-cutting, in order to determine the lateral boundaries of the ore, is safer than to rely on supposed walls. A so called "slip" has often been followed by a miner as a supposed wall, until by accident he broke through and found good ore on the other side. If veins are formed according to Mr. Emmons' theory, the occasional loss of one or both walls is easily accounted for,

Cross veins of a more recent age sometimes cut or fault an older vein, The point of intersection is generally rich in mineral. Cross veins must not be confounded with

Impregnation of Rock by Vein,

leaders," which are the filling of minor cracks extending off from the vein, and are sometimes sufficiently profitable to work, While they sometimes lead a prospector to the main vein, they may also lead a miner underground astray from the true vein,

The splitting of a vein by a" horse' or large fragment of the country lying in the vein, may be mistaken for a true cross vein, or the original fracture of the fissure may have been in the form of a star or like the spokes of a wheel radiating to the hub,

In such cases there are no true cross veins, But when, as in the San Juan district, we have two well defined sets of veins, one striking northeast by southwest, and the other northwest by southeast, they cut each other diagonally, the cut vein being the older, "These opposite sets of veins have been formed at different times, Many contain a characteristically different class or variety of minerals. Thus in Cornwall, England, one set carries tin and the other lead,

Signs Of A True Fissure Vein,

True fissure veins show signs of motion or slipping on the sides of the fissure, such as. slickensides, gouge, crushed walls, horses," or breecia,"' the latter being small portions of the country rock surrounded and cemented by vein matter. In the Comstock, the quartz is ground to powder, The vein itself, though occupying a healed fault fissure, may be itself faulted by later movements in the mountain after the vein was formed, Some of the fissure veins on Engineer Mountain, San Juan, are so dislocated,

The vein-filled fissures being a line of weakness, may PLATE LVII. be re-opened by mountain Combed, Banded or Ribbon Structure movements, and other or dif- with Quartz Geode. ferent combinations of ore introduced into the heart of the vein. Such a reopening would be marked by a succession of "combs" or banded ribbon-like deposits of ore, and by gouge matter.

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Outcrop Of Veins.

The outcrop of a vein is that which appears at the surface and usually attracts prospectors to the spot. Sometimes it may be, as in the San Juan district, a bold vein of hard white or rusty quartz, standing up in relief, by its superior hardness, above the surrounding country like a low wall. Or again, in the same district, from being composed of softer or more soluble substances than the prevailing eruptive lava sheets, instead of a wall it causes a depression or trough on the side of a hill, forming the pathway fora rivulet and marked by luxuriant vegetation. Commonly the outcrop consists of a decomposed mass of rock, stained with oxide of iion and streaked here and there with green or blue carbonate of copper, and is called " float" or "blossom " by the miners. This "float" is the chemically changed or oxidized portion of the true and unchanged vein lying deeper below the soil. On Aspen Mountain the float is generally a rough crystalline mass of calcspar and baryta stained with iron and copper.

In this "blossom rock" free gold is not unfrequently found, but unaltered sulphides, such as galena or iron pyrites, are rarely mei with on the outcrop. In the San Juan district, on Mineral Point, we have, however, found

alena at the grass roots, and broken off large chunks of it rom a quartz vein outcropping on the surface.

In gold-bearing veins such an oxidized condition is desirable if it continues down to any depth, for, so far as it continues, the gold is free, and the ore is a free milling one, easily treated, and often exceedingly rich in gold, as in the celebrated Bowen mine of Del Norte; but as soon as the hard white quartz and the unoxidized pyrites of the true vein is reached, the ore is no longer free milling, but must be smelted. The gold may still be found free, perhaps, in the hard quartz, but if the pyrites should not prove rich in gold, the palmy days of the mine may be considered as past. Many such rich deposits on the surface, abounding with specimens of free gold, have proved great disappointments with depth.

Width Of Veins.

Veins may vary in width or thickness from a half inch to a hundred feet. They also pinch or widen at intervals in their downward course. The widest "mother" veins are not always the most productive, though they are very per-

; @'

sistent in length, and we may suppose indepth also. in the Saag bole district the "mammoth" veins of quartz, often

hun the ore being found too much scattered in them, and the

red feet wide, are not the favorites for development,

Plate Lviii.

Metalliferous Veins Exposed to View near Howardsville, San Juan, Colorado, Showing Two Systems of Fissure Veins Crossing One Another,

development less easy than in those Io, 20 or 30 feet wide, where the metal is more concentrated. These mammoth veins in the San Juan are easily traceable for miles over the surface of the country and down the sides of the deep

go

canyons. Their limiting depth has never been reached, and probably never will be by mining.

Definition Of True Fissure Veins,

True fissure veins are popularly defined as filling fissures of indefinite length and depth, commonly occurring in parallel systems, traversing the surrounding rocks independent of their structure or stratification, and commonly, though not necessarily, at an angle different from that of the stratification—in other words, cutting across the planes of stratification. These veins originated in fissures, not necessarily wide open ones, but on the contrary, rather narrow cracks descending, however, to great depth such as those produced by faulting, or the general cleavage lines of the mountain, The latter may be frequently observed in every canyon, and also in the sedimentary rocks of the foothills and even along the flat surfaces of the plains. They

PLATE LIX, are very conspicuous in the

Fissure Vein Conforming in Part to plains around Trinidad, and

prey sceanees piraticnton are there not unfrequently

occupied by a series of narrow

parallel dykes of basalt instead of by mineral veins. Cleavage lines or joints are familiar to every stone-quarry man.

These cracks are caused by extensive movements of the earth's crust in the process of mountain uplift, and also on a smaller scale by co,:traction of the rocks in cooling froma heated or molten condition, or even in consolidating from a soft or muddy condition.

The two walls enclosing a vein do not generally coincide, as might be expected, if the vein occupies a line of fault. A true fissure vein may in some part of its course coincide with the dip of the surrounding strata. As the plane of stratification or line of division between one stratum and another is a natural line of weakness, a crack once started would be liable to follow it for some distance. And when uplift occurs such places are liable to slip one upon the other, and a true parting fissure ensues conformable to the prevailing dip. Such a vein might appear at first to belong to the class of so-called " bedded veins," but if with depth

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it should be discovered to be cutting across the strata it would be pronounced a "true fissure vein," The appearance of slickensides or other signs of motion on the walls of the apparently " bedded portion " would then prove it to belong to the 'true fissure" class, and that actual fissuring had taken place prior to the vein-filling.

Cause Of Pockets In Fissure Veins.

As a fault fissure in its downward course usually pursues a zigzag rather than a straight course with smooth surfaces on either side of the crack, the inequalities of one face of the crack are brought into opposition to the inequalities on the other WY face, as one or the other side of the fault YY slips up or down, and thus are produced Y pinches and wide cavities, which give rise to the "pinches" and " bonanza pockets" Yy so common in fissure veins. A so-called Yyy true fissure vein may sometimes have ad- Lj vantages over some other forms of vein occurrence, from its persistency and comparative regularity to great depths. It Gy must not, however, be expected that it ; will continue equally rich or equally poor throughout its course. There may be com-

paratively barren spots and rich spots, L pinches and widenings, local combinations Ui, of richer or poorer varieties of mineral. Z

But the vein asa rule is not likely to entirely give out.

Richness With Depth.

There is no scientific reason why a vein should "grow in richness and size with depth." This is a popular fallacy, originating from the now less accepted theory that veins were formed by the precipitation of ' precious metals, by heated rising waters or Pocket and Pinches

resulting from slipvapors, and hence that the greater con- ping of uneven Walls centration would take place at greater of Fissure. depths. The "lateral secretion" theory, now by some accepted, ascribes the deposition of ore to solvent waters reaching the vein from ground quite near to it and coming naturally from above and the sides quite as often as it is ejected upward by pressure from below.

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In Idaho Territory, says Mr. A. Williams, "the rule is rather that veins grow less rich and strong with depth, though strong veins may continue metalliferous to a greater depth than mining can ever reach.

"The thickness of the earth's crust which we are able to explore is very limited. Increase of heat, as in the deep Comstock mine, and other natural difficulties, limit us to a few thousand feet—3,000 at most. These deep mines have not, as a rule, proved richer with depth, but to the contrary. Some veins have been worked through alternate zones of richness and barrenness. The Comstock, which has been opened for four miles in length and to a depth of 3,000 feet, shows the ore bodies to be scattered irregularly and the barrenest ground is at the bottom. On the other hand some of the most celebrated mines derived their wealth from rich ores encountered near the surface and have proved most disappointing with depth."

Atmospheric action for a long period has often reduced the ore to its richest compound, and when the hard material is reached, leanness sets in. This, as we have observed, is commonly the case with gold veins. The richness of the Leadville mines is derived from their decomposed compounds. Again, as the surface crust can be so little explored by mining, it is to be remembered that the erosion by glaciers and waters has already removed thousands of feet of the vein, so that we are able to examine only a small fraction of it, while an unknown quantity lies in the depths below. If these veins, then, continue to the supposed great depths below, we are very far from their starting point, and erosion having removed their upper portions, we cannot find their surface finishing point; in other words, it is not a fresh "ready made" vein we find, but portions of an old vein already extensively mined by the processes of nature.

So far as our experience goes in Colorado, after a moderate depth is reached below surface action, or below the "water level," a fissure vein may grow richer or poorer, wider or narrower with depth, without any law except local experience in a district.

Veins In Groups.

Fissure veins occur in clusters and nearly parallel groups, forming a mining district, and again in that district certain peculiar veins may be grouped together, forming a " belt." Thus Boulder district occupies a certain isolated area, out-

side of which few mineral deposits occur for a long distance. We have also in that district several distinct belts carrying different characteristic ores, such as the telluride belt, marked by rare telluride deposits, the pyritiferous goldbearing be!t, and the argentiferous galena belt. The Central City region is characterized by auriferous pyrites belts, Georgetown district, not far distant, by argentiferous belts, and Idaho Springs, lying between the two, by both gold and silver belts.

Chapter Viii. Relation Of Veins To Eruptive Forces.

The ultimate cause of the richness in veins of a district or locality is, that local dynamic and eruptive forces were more energetic there than elsewhere, causing great disturbance of the rocks, accompanied by fissures, and eruptions of por-

hyry. e thus at Leadville, the Mosquito range is violently folded and fractured, eruptive rocks have issued abundantly, and associated with such phenomena we find great lead and silver deposits.

Further south the great San Juan district is split up in an extraordinary manner with great fissure veins. The region is an eruptive one, consisting of prodigious flows of eruptive rocks traversed, not unfrequently, by newer eruptive dykes.

In the Gunnison district the strata have been overturned, disturbed, folded and faulted in an extraordinary manner by the intrusion of great masses of eruptive rock forming the peaks of the Elk Mountains. The strata everywhere are riddled by dykes or intrusive sheets, and the evidence of heat is apparent in the general metamorphism of the entire region. Mineral veins abound. The same phenomena are repeated more or less in the neighboring region around Aspen, and at Pitkin and Tincup.

Xt Boulder, Central and Georgetown there is a concentration of eruptive dykes heger in each district, and few dykes or eruptive rocks outside of those districts. On the other

hand we have no ore deposits in the undisturbed rocks of the plains or the flat basins of our parks, and notably our mining districts are for the most part well into the core of the mountains, where, in the nature of things, folding, crump-

ling, faulting, eruptions and metamorphic heat were more energetic than along the flanks and foothills of the range which have usually proved unproductive.

The older eruptive rocks such as the quartz, porphyries and diorites of the Leadville, South Park and Gunnison districts, are more favorable to the production of ore deposits as a rule, than the more modernly erupted lavas, such as basalt or dolerite which we commonly find occurring in dykes and surface overflows, traversing or capping our Cretaceous and Tertiary coal fields along the foothills as at the Table Mountains at Golden and Trinidad.

Some of the lighter colored and somewhat recent lavas like the tufaceous rhyolite, which caps so many of the Tertiary mesas on the Divide between Denver and Colorado Springs have also hitherto proved barren. Yet the volcanic rhyolites, andesites and phonolites of Silver Cliff, Cripple Creek and Creede are productive of both goldand silver. A large portion of the eruptive rocks of the San Juan region, productive of gold and silver bearing fissure veins, are in andesitic breccias of comparatively modern date. The older eruptive rocks, as we have stated, are nearly all of an intrusive character, never having reached the surface, while the newer ones bear evidence of having flowed over the country like modern lava streams, as is shown by spongy scoria on their surface, and may be called "effusive."

In Colorado the ore body is not usually found in the heart of an eruptive sheet or dyke of porphyry, so much as at the line of its contact with some other rock, such as limestone, granite or gneiss.

Contact Deposits.

The "contact" ore deposits of Leadville occur at the contact of quartz, porphyry and dolomitic blue limestone.

Some of the veins at Boulder, Central and Georgetown are at the contact of porphyry and granite or gneiss.

Exceptions occur, however, where mineral is found either in the heart of a dyke, or the whole dyke may be so impregnated as to constitute in a sense a vein. These exceptions are generally confined to pyritiferous gold deposits, and telluride gold deposits as at Cripple Creek.

Gold-Bearing Dykes,

Suppose a dyke or mass of eruptive rock to be thoroughly impregnated with gold-bearing pyrites. Near the surface

and often for a considerable depth the rock is decomposed and the pyrites oxidized into rusty iron ore, liberating the gold which is entangled in the "gossan" in wires, flakes or even small nuggets. As long as this decomposed or oxidized state continues, the ore is free milling, but with depth the dyke is found in its primitive hardness, studded with iron pyrites which may or may not prove rich enough for the more expensive treatment of smelting. Such gold-bearing dykes are found at Breckenridge, South Park, also in Idaho Territory, Cripple Creek, Colorado, and in old Mexico, and many other gold-bearing regions.

The Printer Boy gold mine at Leadville is a vertical deposit in a jointing or fracture plane ina dyke ot quartz-porphyry, rusty and much decomposed near the surface where it yielded free gold; with depth this passes into copper and iron pyrites. The vein is from an inch to four feet in width ; stringers carrying ore extend into the porphyry, which is highly charged with pyrites which doubtless supplied the

ee ba vein with mineral through the

Gold ein ot Gold Bearing Dyke; agency of surface waters. In

Portions. Arizona, near Prescott, at the Lion mine we find a green dyke of eruptive diorite penetrating granite. This dyke is traversed by numerous small veins of white quartz which near the decomposed and rusty surface are rich in free gold. At slight depth the quartz veins become charged with unoxidized iron pyrites sufficiently rich in gold to merit treatment by smelting. The surface ore is treated by a simple "arrastra," and is, of course, free milling. The gold seems to be mostly confined to the quartz veins.

Plate Lni.

FISSURE VEINS IN IGNEOUS AND GRANITIC ROUKS, The San Juan district is an exceptional case where immense numbers of fissure veins penetrate igneous eruptive sheets. The fissure veins consist of hard gray jaspery quartz, traversing lava sheets whose united thickness is from 2,000 to 3,000 feet. The veins produce lead, bismuthinite, gray copper and other silver-bearing ores.

In Colorado true fissure veins are most characteristic of the Archzan granitic series. In fact, all the veins in that series are fissure veins. Locally they occur as in the San Juan, cutting through eruptive rocks. Outside of these formations few true fissure veins occur.

An exception may be made of the Gunnison and Elk Mountain region where the fissures traverse all the formations from Archean granite to the top of the Cretaceous coal beds. Nearly all other mineral occurrences, such as those in the limestone regions, come under the class of bedded-veins or blanket-veins, pipe-veins or " pockets" and show none of the characteristics of slipping motion or fissure action. Under this latter class the Leadville and Aspen deposits may be grouped.

Ore deposits commonly occur at the junction or contact of two dissimilar rocks, as between quartzite and limestone or limestone and dolomite.

Lodes occur also between the stratification pianes of the same class of rock, sandwiched in between two layers of limestone, and sometimes impregnating the layers on either side for some distance from the dividing line between the two strata, which is commonly the line of principal concentration of ore, and often descend from this concentration line, through the medium of cross joints, to form large pockets in the mass of the limestone. The Aspen and Leadville deposits are of this character. Also when ore bodies occupy a true fissure, z. e., one cutting across the stratification planes, they may locally, for a short distance, irapregnate the adjacent walls or country rock more or less. Qur fissure veins in granite and gneiss often impregnate the walls to a small extent.

Mineral deposits favor as a rule the older rocks, such as the Archean and Paleozoic series, probably because heat and metamorphic action are commoner in these older rocks which have felt all the throes of the earth from past to present times, than in the more recent ones, and such circumstances, as we have stated, are peculiarly favorable to vein formation and mineral deposition.

The bulk of our precious minerals in Colorado comes from the older Archean and Paleozoicseries of rocks, the exception being the Gunnison region around Crested Butte, Irwin and Ruby, where ore comes from fissure veins in the Mesozoic Cretaceous rocks. The exception is accounted for by the local metamorphism, heat and eruptive phenomena of that region. .

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The veins in the San Juan have also been ascribed by some to the Tertiary Period, owing to their occurrence in certain supposed Tertiary lavas co. ering that district.

Besides heat, metamorphism, dynamical disturbances and eruptive agencies, other minor circumstances may favor ore deposition, Certain rocks, suchas limestones, may offer, by their tendency to solubility and chemical reactions, more favorable conditions than others for mineral solutions to deposit by '"metasomatic"' interchange between mineral and limestone, until the limestone is gradually replaced by ore, much in the same way as the elements of a water-logged trunk of a tree are replaced by silica in the process of fossilization,

Change Of Minerals With Depth,

Lodes often change in the character of their minerals with depth, not only after they have left the zone cf secondary decomposition and surface action, but also far below it. Thus, in the San Juan, some of the mines abound in zinc-blende near the surface, which with depth almost disappears, giving place to gray copper and other superior ores. In Cornwall, England, the shallow workings yield copper, and with depth, tin ; and locally, many such changes may Characterize a particular district but cannot be formulated as arule for other localities.

Influence Of Country Rock,

In most mining regions, to which Colorado is no exception, a relation has been observed between varieties of "country rock" and ore deposits. Veins in passing from one country rock to another are liable to change in the size or variety of the ore, widening in connection with some rocks, and pinching or growing narrower in connection with others.

Certain rocks are notorious ore-bearers, whilst others are notoriously barren over large regions, or in special localities.

The presence of certain rocks adjacent to other different rocks has an enriching tendency on the ore bodies.

As regards rocks that are good ore-carriers or receptacles of particular classes of ore in Colorado, we may say: That quartzites and silicious rocks generally carry more pyrites, and are gold-bearing.

That veins in granitic rocks carry a greater variety of

minerals than others, and may be both gold and silver bearing. ;

That certain limestones carry much argentiferous galena

That sandstones and other unaltered rocks carry little ore of any kind.

The influence of country rock on veins may be from several different causes, for instance :

Certain rocks are by their structure better adapted than others for forming regular fissures. Thus, massive limestone is better fissured than slate or shale, leaving wider open spaces for the ore to collect in.

Other rocks may be more porous, and admit mineral solutions through their pores. Of sucha kind are some of our porphyries, andesites and phonolites.

Others, like limestone, are easily acted upon by solutions dissolving out the rock and replacing it with mineral by substitution.

Some are better conductors of heat, and therefore would assist chemical action and mineral solution,

And lastly, if modern theories of "lateral secretion" be true, viz.: That most ore comes from the adjacent country rock and is precipitated, substituted, or collected in the vein fissure, and further, that the metals themselves are derived from certain metallic elements in the ordinary constituent minerals of the country rock, such as mica, hornblende, or augite, it is clear that a rock composed largely of such minerals would be liable to influence the vein as an ore generator. Granite, porphyries and andesites are largely composed of these minerals.

The frequent presence of eruptive porphyry rocks near veins and ore deposits in Colorado shows that they have an important influence on those deposits, which may be of various kinds,

First, that in their component minerals and mass they actually contain the elements of the precious metals subsequently deposited in another form in the fissure vein or in the soluble limestone in contact with it.

Second, by the heat which they retain for a long time after they have congealed and hardened, they would assist in the reactions of any chemical or mineral solutions that might be on hand. Lava, at the time of its eruption, is always highly charged with steam and other gases. By reason, also, of the chemical composition of porphyry, waters passing through it would be alkaline and assist in dissolving silica and other gangue or veinstone matter, and

when the porphyry has thoroughly cooled it is exceedingly porous, and being much jointed and cross-fractured, becomes like a great sponge for the absorption of all surface waters. This may be noticed at Aspen, where all the mines that are at present penetrating through the " porphyry cap" are much troubled with water, far more so than in the underlying limestone. Surface waters, then, becoming alkaline by passing through this rock, and also more or less charged with carbonic acid, chlorine, and other solvents, would be ready to dissolve both gangue and vein ingredients out of the porphyry and redeposit them in the vein fissure, or, by metasomatic substitution, in the limestone usually beneath it.

Water circulating in fissures, changes or dissolves the ingredients of the surrounding rock, The rocks enclosing lodes are always so altered, and this decomposition and alteration is not always merely local or confined to the close proximity of the ore body, but we often find a whole mining district, such as Leadville, Aspen and San Juan, pervaded by this feature. So much is this the case that it is often difficult to get a fresh, unaltered specimen of porphyry or some other country rock within the district.

The brilliant red, yellow and maroon tints that color so much of the mining district of San Juan result from the oxidation of pyrites and other iron-bearing minerals pervading the eruptive rocks, and it is noticeable that this color, resulting from alteration and decomposition, is most prominent in those parts where lodes have been discovered, as, for example, the gorgeous tints of the Red Mountain area around the celebrated '" National Belle," " Yankee Girl," and Ironton mines, between Silverton and Ouray. The rocks in Geneva Gulch, Hall's Valley, Buckskin Canyon, and in other mining centers, display ihe sume beautiful tints of oxidation in the vicinity of the mines.

"In lodes a mutual exchange takes place through the reaction of the ingredients of the rock and the materials of the vein. Thus, when water containing carbonates comes. in contact with rocks cx minerals containing alkalies, a chemical reaction takes. slace. When these last are combined with silicic acid, these silicates are decomposed by the carbonic acid and the bicarbonates. This explains both the crystallizing out of the carbonates and the so frequent decomposition of rocks containing lodes, especially those which, like our veins in granite, are feldspathic."

The same principle applies to other ores and minerals in

lodes. Thus the precious metals, in the mines of Leadville in their original condition, have been proved by depth to have been in a sulphide state, such as iron pyrites (sulphide of iron), or galena (sulphide of lead, etc.). Surface waters charged with carbonic and other acids, passing through the overlying porous alkaline porphyry and entering the underlying limestones, have, as we have previously observed, change the sulphides into sulphates, oxides and' carbonates.

The presence of a dyke near to or cutting a vein has been found often to enrich the latter at the point of contact.

In the " Colorado Central" mine at Georgetown a narrow dyke of brown obsidian traverses a large dyke of ore-bearing porphyry. The valuable ore is found close to the obsidian dyke. This might be the result of greater heat at that point. The "black dyke" in the Comstock mine isa somewhat similar case.

Prejudice In Favor Of And Against Certain Rocks.

There is often a prejudice amongst miners in favor of certain rocks and formations, aud against others. Miners who have worked perhaps in the great Comstock mine of Nevada, or the Leadville mines of Colorado, or the fissure veins in granite of the Old World, are apt to look out for and favor certain rocks and formations they find like those they have been accustomed to. Thus, as Mr. Williams says, % The peculiar 'porphyry' of the Comstock was hunted up in other districts, but did not prove metalliferous. Solid granite was looked upon by others as unfavorable, generally, because locally some granite above the gold belt of California had proved barren. Yet some of our best veins are in granite.

" Limestone was at one time a very unpopular rock and supposed only locally to produce lead, till the discoveries of Leadville, and Eureka, Nevada, overturned the scale in its favor."

In the Leadville "excitement " not only was the particular Carboniferous limestone of Leadville hunted for and prospected, but every other limestone in the South Park region, no matter what its geological age or position, was extensively prospected without results, miners not recognizing the fact that it was not limestone generally that produces rich ores, but a Jartzcudar limestone of a particular geological period (the Lower Carboniferous) not over 200 feet thick,

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that happened locally to be rich near Leadville, and the reason of its being locally rich at that point was owing to the concentration of eruptive energy at that point and the intrusion of an nirarewal amount of porphyries, which in oint of fact are far more responsible for the ore than the linestone which happens to be merely the receptacle.

It was also quite common after the Leadville excitement to find shafts in all sorts of improbable and_ hopeless localities whose owners would tell you: " At Leadville it didn't matter where a man 'went down.' It was all luck whether you 'struck it' or not, and so they might as well 'go down' where they were as elsewhere." It was often said "that Leadville had exploded all so-called scientific theories about ore being in one formation or locality more than another. It was all a case of luck."

The excuse for tnis is to be found in the fact that in the immediate vicinity of Leadville it did scarcely matter " where you went down," seeing that that area was practically underlaid by bedded sheets of mineral, but that such would be the case elsewhere and everywhere or anywhere, experience unfortunately has shown to be untrue, It is not a particular rock or formation, but a combination of favorable circumstances that alone can make a rich mining district.

As experience advances, geologists and miners have proved that ore deposits have a much wider range than was once supposed. Formerly only the Archean yranite series was supposed capable of bearing ore deposits, because in the Old World, tin, copper and lead came principally from fissure veins in those rocks. Then deposits were found in the Paleozoic series and supposed to ascend no higher. But in the present day, and even in Colorado, they are traceable even to the Tertiary.

It is not the rock, nor the age, but a combination of circumstances, principally heat and metamorphism, that may make any rock of any period an ore-bearing one. And in prospecting in new regions it is these combinations rather than any particular rock that should be looked for.

Strike And Dip Of Veins.

The dip of veins approaches more nearly the vertical than the horizontal, daually from 75° to verticality. Nearly all our ore deposits, in Colorado, even those of the bedded class, dip more or less steeply from 25° to 75°.

For a few feet from the surface, on the steep slope of a

mountain, it is common to find an ore deposit dipping quite gently or even folded over and dipping in_a contrary direction to that which it assumes with depth. This appears to arise from the weight of the strata above it tending to bend it over downward in the direction of the slope of the hill.

There is generally a prevailing dip and strike amongst a number of parallel fissure veins of a district. In the San Juan, the bulk of the fissure veins have a prevailing northeasterly strike and dip to the southeast. The angle of dip is generally between 60° and verticality. CROSS-CUTTING UNCER-

Tain.

The dip as we have said, not unfrequently changes. considerably with depth, usually be-

PLATE LXII. coming more and more

Showing How Cross-cut Tunnels and Shafts vertical. From the de- May Miss Veins by Change of Dip or gree of uncertainty as to Faulting. the continuity of the dip, it is not always safe, on

the discovery of an outcrop, to endeavor to cut it at a much lower point, so as to get the coveted depth, and better opportunities for stoping, drainage and other developments. of the rain. Owing toachange of dip or fault, perhaps, the miner may have to makea much longer cross-cut tunnel than he had calculated upon before striking the vein. Sometimes, too, he may miss the vein altogether, cutting it perhaps at some point where it is exceedingly thin or poor, so poorin fact that he passes through it without noticing it or believing it to be the same vein whose outcrop looked so promising on the surface. Cross tunnels through "dead rock" should hardly be undertaken until the vein has been proved to be a strong one fora considerable depth. As we have already shown, great depths may not after all be so desi:able in even a fissure vein, as there is no certainty whatever about veins becoming richer or poorer with depth. Extensive cross-cut tunnels have seldom proved paying concerns. The greatest in the United States, the Sutro

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tunnel, six miles in length, which tapped the Comstock fissure at a depth of 2,000 feet, did not prove a financial success, and had it tapped the fissure still lower, at 3,000 feet, it would have found the vein in the impoverished condition it is to-day. It is not uncommon fora miner to strike a rich outcrop on the top of some mountain, and on the strength of its richness induce a company to run a long cross-cut tunnel in "dead rock" half through the mountain to cut this vein, and the company's resources are nearly exhausted in so doing, while the vein itself gives no returns, owing to its being left idle. ; Finally, perhaps, the vein is missed, or if struck, proves far poorer than was anticipated. Of course there are exceptions where cross-cut tunnels in "dead rock" may be advisable.

If a fissure vein, as in the San Juan, should outcrop near the top of a mountain and be exposed on its dip all the way to the bottom, there may be some reason

for opening a tunnel in it PLATE LXIII. near the base, the reby Fissure Vein Exposed From Outcrop to facilitating drainage, de- Dip.

velopment and exportation.

In that case the miner is om the vein, with no fear of losing it; but even here, there is no guarantee that it will prove rich all the way to its outcrop a thousand feet above. " Follow your ore, and be ontetat" how you leave it for any experimental theories," is a common and wise saying among experienced miners. We remember a tunnel in the Gunnison region which was run several hundred feet at a cost of many thousands of dollars, all through "dead rock," in the hopes of cross-cutting a certain ore body that had proved rich near the surface. At last it was given up, and subsequently a short cross-cut was made from it, and the original vein was found only a few feet from the tunnel, which had been running parallel with it all the time. The cause of the mistake was an unforeseen fault in the vein that had shifted its dip much further on one side than had been calc: .iated upon,

Chapter Ix. Gold Placers

Prospecting For Placer Gold And Gold Veins,

Having given in preceding chapters a sketch of veins and ore deposits in the rocks, it follows in order to speak of gold placers, because these are derived from. the former by the agencies of water, either in the form of glaciers of old, or of ancient or modern streams.

The glaciers in olden times heavily mined the rocks and the veins, by cutting broad gashes through theni, thus originating the canyons. In this way millions of tons of rock were mined, together with the goldbearing veins in them, and also the precious metals minutely diffused and scattered throughout their masses.

After the glaciers, the rivers took up

Open Placer Grounds in Canyon. the work, deepened

the canyons, broke

up the boulders and sorted them, setting free the gold and

other metais they contained, and again sifted and sorted

them and deposited them along their banks and in their beds.

Of the various metals thus handled by nature's jigging process, many were dissolved and destroyed by various acids in the waters, and by acids of vegetation and iron salts

ercolating through the placer dumps after they had been aid down. So with the exception of a few very hard minerals, such as magnetite, diamonds, garnets, rubies, etc., little remained in the placer but the imperishable gold, and even that appears to have been refined of its alloy of silver which it contained in the original vein, for placer gold is generally much purer and more valuable than that in the original vein. In some cases, too, the fine gold disseminated through

Plate Lxiv.

cart

the placer appears to have been acted upon by certain silts, such as the persalts of iron, and concentrated and amalgamated into large nuggets. Some contend, however, that these nuggets are only waterworn pebbles of gold, brought direct from the vein, the result perhaps of concentration there of the contents of large masses of gold-bearing pyrites ; it is to be noted, however, that whilst gold-bearing nuggets of various sizes are to be found, not uncommonly in gold placers, they are very rarely found in gold veins.

With the gold in placers, is commonly found what is called "black sand," which is composed of grains or pebbles of magnetic iron ore, relics of the old gold-bearing pyrites chemically changed. Being near in gravity to gold, and originally associated with it, the two are generally found

Plate Lxv.

Section in Gold Placer.

together in a placer, and a prospector in surveying a bank of placer-material made up of sand, pebbles and boulders, generally looks for a streak of "black sand" as a likely place for gold. Also by reason of the gravity of gold he is inclined to look for it more down on bed-rock than in the upper looser strata.

Ancient river beds as well as those of modern rivers may be found gold-bearing, rivers that have long ceased to flow, by reason perhaps of change in the configuration of the country. In California and Australia many of these ancient gold-bearing river-beds have at a period not long distant, been deluged and covered by lava, and the goldis extracted by tunnelling beneath the lava-sheet or by shafting down through it to the gravel below. These are called deep leads whilst the ordinary uncovered gravels are called "shallow placers."

Almost anywhere along ancient or modern water courses not far from mountains, a prospector by panning, can get colors of gold even on the pebbly "wash" covering the surfaces of large portions of our plains, or even on the tops of table lands that once were plains, over which broad rivers and glaciers and large bodies of water distributed their debris, but as a rule it will only pay to work where the "wash" or "drift" or "alluvial" matter is plentiful and thick, and more than this, only where water is accessible to the work.

Prospecting,

A prospector hunting for a gold placer follows up the water channels in which he finds specimens of all the rocks in the neighborhood. In Australia, the prospector looks amongst these to find samples of granitic, porphyritic and quartzose rocks or clay-s!ate as likely signs, and also pieces. of quartz honey-combed and rusty, which we have described before as " float or blossom."" Plenty of broken up quartz he considers a good sign, but very pure, hard, dull white quartz is generally considered as "hungry" or "barren;" the size of the fragments denotes his nearness or otherwise to the reef, z. ¢., the vein.

A prospector examines closely the fine sandy matter of the stream bed especially where eddies and backwater have been formed. A likely deposit should be scraped up, even down into every crevice and depression in the bed rock or solid rock bottom over which the river, modern or ancient, has worn its channel. This material should be panned. Gold, too, is often found on points and slopes of the bed rock as well as in the deepest portion. Nuggets found on high reefs above the level of the stream, imply that their weight enabled them to remain in their position, during the deeper erosion of the neighboring streams, and that the original vein from which they came, is not far off. As a rule, large nuggets and coarse gold are found much nearer to the source whence they came, than fine or " flour" gold, which is often carried to unlimited distances away out on the plains.

The character of quartz veins and of their enclosing rocks in the immediate vicinity, decides the character, too, of gravels derived from them, hence sometimes a peculiar pebble may be traced up to the peculiar rock whence it came, and the gold vein be found near it in place.

It has been observed that "leads" fo/lowing the course or lines of a gold-bearing reef, maintain a more continuous.

yield than those cross¢ng a number of gold reefs at intervals. Gold occurs in pockets and "shoots" at intervals, with barren portions between, which accounts for what we have stated above. In country where the gold quartz veins are small, though rich at wide intervals, the gravels will also be small.

In very deep ground where the "wash" is very pare a series of borings or even shafts are made to test the quality of the bank. The following points have been observed as worthy of note in prospecting for gold placers.

1, Streams crossing the lamina or stratification planes of gold reefs at right angles are likely to be richest.

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2. Gold is rarely found plentiful where there are indications that the current was strong, but rather in the lee under projecting points of rock, where beaches are usually formed and the water was slack.

3. Gold in streams is deposited in crevices of the 'bed rock," which should be laid as dry as possible and picked ° up to such depths as the sand descends between the laminations.

4. Terraces are shelf-like excavations and deposits upon hill slopes above valleys, and are the remains of old glacier or river beds. The prospector should discover the inlet and outlet of the terrace and examine the gravel. The ' wash" sometimes contains gold in layers one above the other.

5. Whilst working up stream attention should be paid to the banks on each side where sections are exposed so that no outcropping vein be overlooked.

6. Alluvial gold should if possible be traced to its source

whence the "float" came. When the gold is large and plentiful and the boulders large and angular the reef is likely not far distant. 7. Sometimes there isa dist.nct peculiar feature in all the veins of a district, such as a peculiar band of a definite color. 8. Coarse alluvial gold is not always incompatible with fine reef gold as a source, because the reef gold may be so fine in

PLATE LXVII. Shallow Placer—Gold Sand Behind Bar on One Side of Creek.

general as to lend itself to very wide distribution when once it is liberated, while the rarer coarse grains would not be transported far.

g. Alluvial placers are richest where the current of the stream is interrupted by diminution in fall, by sudden change of direction, or by entrance of a tributary, also by reefs, bars, eddies, etc. Absolute richness depends upon local circumstances and the size and weight of floated masses,

10. Creases, holes and fissures of bed-rock over which the stream passed are favorite places.

11. The lowest layers of each separate period of deposition are the richest.

Sometimes several different periods of deposition have succeeded each other.

12, The courses of present streams and of ancient channels are placers.

"LOAMING" is a form of prospecting. It is preliminary to such peeps tee as cutting experimental trenches, or sinking trial shafts or boring. It consists in washing surface prospects from the bases and slopes of the ranges, until specks of gold, or specimens are found to be obtainable with tolerable frequency, within certain limits. The prospector then proceeds to trace the gold up hill to its source,

narrowing the limits of his work as by patient search he approaches the vein, whence the gold has been derived. When he can obtain surface prospects of gold up toa certain point, or line, but no farther, he then proceeds by means of trenching to search for the gold vein, The prospector has often to work along a steep scrubby mountain side selecting his prospects, numbering them, and placing samples in his "loam bag." If he discovers prospects of gold, he finds his way back to the spots the samples were taken from, so as to continue his up-hill search, and trace the gold to its source or vein, Sometimes there is no indication of a vein, soil and bushes and debris covering its out-crop, but by loaming, the prospector ascertains its position, so as to expose it by a trench not many feet in length.

We remember an ingenious way in which a valuable and

long sought for vein was at last discovered. Prospectors had long found very rich "float" at the base of a hill whose surface was so deeply covered with loose debris that no trace of the vein could be found, A prospector found a small lake on top of this hill, and conceived the idea of cutting a trench from this body of water to the edge of the hill, and by damming up the trench, and then suddenly letting out the water to full force, it cut a deep trench through the loose debris down to bed rock and the vein was discovered. This process is called '' booming." ; The cleavage of quartz is said to be freer, sharper and better defined, in gold-bearing quartz than in that which is barren. Pyrite is a good indication. A soft, fatty clay or gouge often flanks the vein in its gold-bearing portions.

The mountain spurs should first receive attention for veins; if the quartz is hard, it stands up, if soft, as it more commonly is, it will leave a streak-like depression, On finding such, the prospector should first wash out some of the decaying rock. If only trace of gold is found in the quartz, there is probably a gold vein in the neighkto1hood, and trenches should be dug and exploration systematically followed up. Gold is generally near one wall of a vein, seldom all through the stone. Quartz gold occurs in "shoots" with barren spaces.

Before setting a valuation on a discovery, the facilities for working the mine, such as we have alluded to, should be considered. Placer mines as well as other mines are often supposed to be " worked out." These are sometimes well worth investigating and examining by cross-cuts or other

means, Sometimes it happens that more gold is obtained

from "leader" veins that had been overlooked, than from

the main worked vein.

) Quite commonly, especially in the lower part of a placer,

i the pebbles and sand are firmly cemented together intoa coarse conglomerate by infiltration of iron oxide and clay,

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t This may consolidate into a false-bottom and not be true "bed rock." Generally two or three such false-bottoms, with intervening strata of greater richness, alternate with

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barren ones, So, many old diggings, thus supposed to have been exhausted, may be worked again, the true bottom not having been reached. These conglomerate bottoms may lie just upon bed-rock, with a white ae rich in gold beneath them. Gold occurs also in the conglomerate and must be stamped out. i Modern rivers frequently cross in their course old river courses, and redistribute their golden sands, Placers are richer in their richer parts, than the veins from which their gold was derived. i When shallow placers are due to the wearing down of quartz veins, no piacer will be found above these veins, or above the point where the vein crosses the placer. In the Sierra Nevada there is but little alluvium, the gold comes from veins near by. Gold placers may sometimes occur below silver mines. Thus.the Comstock vein was discovered by following up lacer gold to its source. This vein has produced a goldearing silver-ore, the silver rapidly disappearing and leaving the gold behind.

Example Of A Placer,

In Ballarat, Australia, the " wash-dirt " runs ina series of "leads" of varying width, starting from the same point, and trending in different directions towards the "deep leads." The "reef wash" is about 100 feet deep, the "pay dirt" 5 feet. The barren drift wash overlying the "pay dirt" is of black clay. The reef itself is of green slate, the bed-rock is sandstone. Gold lies sometimes on thin layers of sand or ''pipe clay" on the surface of the " bed-rock," more often in crevices of the bed-rock itself, which is more or less it rotten. This bed-rock is broken up for some 12 to 20 inches it and the gold is found in "pot-holes" in it 15 to 18 inches in diameter and 6 to 10 inches deep, cut out of the solid rock. The alluvial gold is found chiefly in bed-rock of slate, dip-

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ping go degrees. Some of these slates are soft and rotten, others are indurated. On the soft rock only is the gold found, Nuggets are found in the soft clay lying on " bedrock," Slate forms natural "riffles' for catching the gold,

Deep pools under waterfalls in gold-bearing streams rarely' carry much gold. So in rivers, gold is found in " bars" or points rather than in deep pools or bends,

Chapter X. "Deep Leads,"

A "deep lead" lies deep below the surface, often covered by beds of lava, sapectaily in California. These lava beds may be many in number, and hundreds of fet in thickness. The "deep lead" is an ancient river bed.

In the Sierra Nevada the gold is derived from metamorphic crystalline rocks of the range, partly from quartz veins in the slates, and partly from gold distributed in minute quantities all through the metamorphic rocks. The quartz veins lie between the planes of stratification of the slates, also in irregular bunches and lenticular masses of limited extent. In many localities, the rocks are penetrated in every direction by little irregular quartz veinlets, which often carry gold, and in spots are extremely rich, even where the quartz vein is only an inch thick. In some California districts, wherever a basalt capping exists, the drift beneath it is auriferous.

In California the modes of occurrence of auriferous gravel deposits are various.

"Sometimes they exist in well-defined ancient riverbeds under a capping of basalt which has filled the channels of the rivers in past ages. Again, they appear in isolated mounds or Rilloelee, evidently ihe remains of such channels, which, being unprotected by a covering of lava, have been broken up by the action of the elements, also in basins or flats which have received the wash of these disintegrating rivers, also in low, rolling hills near the base of the Sierras, and beyond the reach of the lava-flows." One of the most remarkable and important gold leads is that beneath Table

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Mountain in Tuolumne County, '" The waters percolating through these lava-flows and reaching the gravels beneath, are charged with alkali from the lava, These alkaline

waters are charged with silica in solution from the same ( source. Hence the fossil drift-wood of these ancient rivers . Lh has all been silicified by these silicious waters. The gravels are also cemented by the same material, These percolating waters also contained iron, for iron pyrites is found in contact with the silicified woods. In this iron-cement, gold is found in rounded grains and in minute crystals, and threads deposited by a solution of sulphate of iron at the moment of the reduction of the latter to a sulphide."

Plate Lxviii.

Mi) Deep Placer, Table Mountain, Cal.—A A, Ancient River Channel, with Cold-bear- Hf ing Gravel; B B, Sandstones and Shales with Fossil Bones and Silicified Wood, Hey

i The dead rivers of California are on the west slopes of the yi Sierra Nevada, from 500 to 7000 feet above sea-level. The i largest and richest lead is the "Big Blue Lead" traced 65 i miles and even 110 miles. It is parallel with the main

divide of the Sierra Nevada. The live modern rivers run at right angles to it, cutting canyons 1,500 to 3,000 feet deep. The '" Blue Lead" runs across these ridges from 200 to 1000 feet below their summit. The lead was discovered by following up surface washings. Miners found that the modern streams were richly gold-bearing up to a certain point, increasing as this point was neared but ceasing when it was passed, These parts were in the line of the different streams, and by following up indications, the lead was eventually struck on several sections and tunnelled on. The deposit is 300 feet deep, composed of gravel, boulders, clay, and sand, on strata distinguished by degrees of fineness, by the character of the rocks, and the amount of gold, also by

colors, the prevailing color being a blue-gray, Gold is coarser near the bottom, and contains a greater alloy of silver, The silver in the gold in the upper strata, has been eaten out by sulphurous acid resulting from decomposition of iron pyrites. The whole deposit is like that in existing rivers, showing banks, bars, sidiae, falls, rapids and riffles, There is much gold in the eddies and but little in the rapids, The space between the boulders is filled with sand and contains gold, the bed-rock is slate.

Where dead-rivers meet, the "wash" is generally rich, Where a lead becomes very narrow, dips fast, and is inclosed between steep walls, the gold will be very sparingly distributed in holes and behind ridges and will be coarse in size,

Very large and abundant boulders in gold-bearing stream beds are often a serious obstacle in getting out the gold, from the difficulty of handling them. More than one placer has been abandoned from this cause alone.

Hydraulics,

Placer banks are worked on a large scale by "Giant nozzles" or Hydraulics. Before commencing such work the total depth of the placer deposit should be examined and ascertained, and the richness of the strata throughout tested. Shafts should be sunk here and there to bed rock for this purpose, and topographical surveys made tc ascertain what fall and head of water can be obtained, and what outlet also for the tailings, as the latter would soon choke up the work; the ground sometimes may be too flat to dispose of the tailings by stream-power. The choking of outlets is a fertile source of abandoning placers,

Beach Mining.— The beach sands of the Pacific and elsewhere contain minute scales of gold and sometimes platinum, together with a great deal of magnetic iron ore. Winds, tides, and surf act as natural concentrators or separators, in parting the light and useless material from the heavier. Wind drives heavy swells on the beach at high tide together with sandy matter. At ebb of tide, the surf lashes the beach and carries back light portions of the mass with the undertow, leaving some iron sand, gold and platinum, whose weight enables them to hold their place. At low water, miners go down on the beach, scrape up the iron sand, which is generally left in thin layers, stacking it back from reach of the surf, and subsequently washing out the

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be a formidable obstacle.

Example Of Colorado Placer Gold Mines.

California gulch. the site of the present Leadville, furnished a great amount of gold in the early days till the discovery of the lead-silver deposits in place. This discovery, also, was due to placer mining. Whilst examining the gravel in the gulch, Mr. Wood, an intelligent prospector, was struck by the appearance of what the miners called " heavy rock" some of which he assayed. His specimens yielded 27 per cent. lead and 15 ounces silver to the ton. He put prospectors to work to find the croppings of the ore deposits, and in June, 1874, the first "carbonates in place"' were foundon Dome Hill. This was practically the beginning of Leadville. It is said that upwards of 2,000,000 dollars worth of gold was taken out of this gulch in one summer before the mines in place were discovered or opened up.

It is noticeable that California gulch alone furnished almost all this placer gold, whilst Iowa and Evans gulches adjoining it on either side, and carved out of the same series of rocks yielded little or nothing. Why should the smaller gulch contain exceptionally rich gravels and its neighbors be barren?

The richest portions of California gulch were found at bends in the course of the gulch. In one place near Oro. in the narrow bed of the gulch, a gold-bearing cement was found containing hydrated oxide of iron, below the gravel, yielding an ounce of gold to the ton. The gulch-gold was worth $19 per ounce whilst that froin the mines in place only $15. The Printer Boy porphyry containing actual gold veins in place may have been the source of some of the gold in the gravels, together with the oxide of iron resulting from the decomposition of pyrites in the pyritiferous porphyry as a cementing material. Also the " Weber-grit"' sandstones at the head of the gulch have been found to carry small gold veins, and from their abrasion also gold-bearing gravels would have been carried down the gulch. Also of late the rich gold deposits of Breece Hill at the Ibex and Little Johnnie mines have been found.

"It is doubtful," says Mr. Emmons, "whether in general, all or even the greater part of the gold contained in placer

In some beaches much oi this sand contains titaniferous iron ore and if attempts are made to use certain processes to save the finer gold the character of the iron may

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gravels is derived from the abrasion of actual gold veins. Traces of gold may be found in a very large proportion oi the massive rocks which form the earth's crust. Gold veins are concentrations of this mineral in sufficient quantity to attract attention and yield a profit. But doubtless there are a vast amount of smaller concentrations which may escape notice. As the rock disintegrates and is worn away by atmospheric agencies, the gold from these smaller deposits as well as from the larger is set free from its inclosing rock and subjected to the concentrating action of mountain streams.

'Placer deposits are the results of nature's vasi sluicing processes. To bring them into the condition in which they may be made available by man, requires not only the goldbearing rock, which her agencies may grind ur into sand and gravel, but the sifting power of rapid streams, which may carry down the lighter and coarser material, and a suitable channel, in which the heavier particles may lodge, as in the rifles of a sluice box. All mountain gravels. all sands of rivers coming from the mountains, contain a certain amount of gold, but it is only under peculiarly favorable conditions that the gold is so concentrated as to render the gravel remunerative.

'Among the most favorable of these conditions is a comparatively narrow channel having a hard and compact bedrock, and ridges or bends in its course, which by causing a partial arrest in the rapidity of the current shall allow the heavier particles of gold to settle to the bottom, and hold them there when once they have settled.

'From this point of view there is a very evident reason why California gulch should have furnished rich placers, and why the gold which may exist in Iowa and Evans gulches should not yet have been extracted even though the detrital material which has been carried down the gulch should originally have been equally rich in gold.

"California gulch is a valley of erosion, formed entirely by the action of running water, and since the glacial period. It has therefore a bottom or bed of hard rock. Its transverse section is Y shared and therefore favorable for the concentration of heavy particles at its bottom. When comparatively full of water, its numerous bends formed eddies in the down flowing currents, and allowed a longer time at these points for the settling of the surface particles, and as it cuts across many different formations in its course, its bed must have transverse ridges, which have caught some of

the gold and prevented it from being carried farther down the stream.

" Evans and Iowa gulches on the other hand are glaciercarved valleys. Their courses are straight, their bottoms broad and comparatively smooth. The glacial moraine ma- ) terial with which they are largely filled has not been subjected to the sifting or jigging process to which gravel is subjected in the bed of stream. The lower part of their present beds is cut, not out of rock, but out of the loose gravelly formation of the 'Lake beds.' This later bed, along which the material brought down by post-glacial erosion has been carried, has not a sufficiently hard and permanent bed-rock to allow of the concentration of gold on its surface."

Alma And Fairplay Placers, South Park.

Along the banks of the Platte river are enormous masses of glacial morainal matter consisting of boulders and sand i brought down partly and principally from Mount Lincoln and receiving contributions from side glaciers of the Mosquito range. This material forms undulating banks on eithe: side of the river. This placer "wash," from 50 to 100 feet thick, is worked for gold principally at Alma and Fairplay.

At Alma the heavy bank of "wash" is mined by the giant nozzle. The banks are also cut back into blocks of ground, by water from a flume, which is let out at intervals along the bank above; at each place it cuts a narrow ravine in the loose debris and at the same time makes the banks easier to be attacked by the water of the giant nozzles which rapidly undermine them. The water and sand from these streams run down into the sluices, whose bottoms are paved with discs of wood, forming "riffles'' to catch the gold, whilst the lighter sand is carried onward by the stream. In their "clean up" in the stream bed, they not only wash down to bed-rock, but after hunting with their knives in every crack and crevice of the Jatter, they dig it up for a foot or two, and further examine it. The rock is a jointed sandstone.

Quicksilver is thrown into the sluices, to collect the finer gold which is afterwards retorted. Whilst gold is found all through this bank of "wash" from "grass roots" down to bed-rock, the greatest quantity of gold and largest nuggets are found at " bed-rock " or in its interstices.

The source of some of this gold may be a series of large, but not very productive quartz veins,in granite, near Mount

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Lincoln, whence the main glacier originated. It is also probable that a good deal of the gold came, as said before, from the breaking up of the various rocks in which it was disseminated, more especially the porphyries and crystalline rocks,

In the winter, owing to freezing of the water supply, the work hast be discontinued till the following spring.

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Mining Regions Showing Examples Of Ore Deposits.

Fissure Veins In Granitic Rocks.

Having described in previous chapters the nature of veins, ore deposits, etc., and how to prospect them, it will be of interest as well as profit to the prospector, to learn something of the mines and mining regions themselves. For this purpose we propose giving a sketch of some of the leading mining regions of Colorado and the West, as instructive illustrations and examples of what we have written in previous chapters. As we said in our advice as to the education of a prospector, the best education for him is to go to, and spend as much time as he can in, the mines and mining regions themselves.

We will take first the regions characterized by fissure veins. These veins are in the granitic and igneous districts of Colorado. In the granitic ranges, the mining districts of Boulder county, Gilpin and Clear Creek, are the most noted, the principal mining towns being Boulder, Jimtown, Georgetown, Central and Idaho Springs.

Boulder Mines.

The geological features of Boulder consist in a series of ridges or hogbacks rising up from the prairie and flanking the granite mountains, These represent Mesozoic strata consisting of sandstones, limestones and shales, containing beds of coal and other economic products, but no precious metal. Volcanic action has occurred in their vicinity as

shown by a large dyke of basalt at Valmont. These hogbacks, so universally present, flanking the granite mountains, are, in Colorado, destitute of precious ores. Inside of and west of these is the Archzan granitic front range, consisting of heavily bedded granite-gneiss, profusely traversed by veins of " pegmatite " or very coarse sparry granite, consisting of white feldspar and quartz, with very little mica, and from a few inches to 4o or 50 feet in width; with these also occur some dykes of eruptive rock, some of it a dark black rock like basalt, called "diabase"; others are lighter colored quartz porphyries and diorites. In the telluride belt, whilst pegmatite veins are abundant, eruptive rocks are scarce, but west of the telluride belt, which is more or less confined to a special area underlying the Magnolia, Sugar Loaf, Gold Hill and Central districts, enormous masses of eruptive rock are found, but no tellurides. In the non-telluride districts, such as Caribou, Ward and Jimtown, rich silver ores are found associated with galena, gray copper, etc., and gold ores associated with copper and iron pyrites. Thus there are two or three distinct belts in the region, a telluride gold belt, and a silver belt, and a gold pyrites belt. It is noticed that the entire region has been locally disturbed by volcanic forces, and volcanic rocks abound ; outside of this disturbed region there are no mines fora long distance.

'the Boulder mines are celebrated for the occurrence of telluride minerals, some of the richest and rarest ores occurring in nature. These ores are confined to a belt occupying the eastern part of the district, and nearer to the hogback region of the plains than any other important ore deposits in Colorado.

West of this belt in the Caribou district the ores are argentiferous galena, with brittle silver. In the Ward district pyrites abound, and where it is decomposed the gold is free. The pyrites though gold-bearing are difficult of reduction.

The pegmatite veins containing the ore stand at a high angle and are often very wide, but the rich ores, especially the teilurides, are concentrated in thin streaks and not very continuous bodies. The gangue or vein material is simply an alteration of the adjacent granite, or gneissic country rock, into a more sparry, larger crystalline form, consisting of quartz, feldspar, and $ome mica. This is impregnated with rich mineral, whose source is probably not far to find, the metal elements being microscopically or chemically diffused

through the mineral elements composing the adjacent. country rock, which is sometimes porphyry, and at others gneiss. This impregnation has taken place either along the contact of an eruptive rock with the country rock granite, or else in a pre-existing vein of pegmatite, or along some fault or jointing plane in the country rock itself which has been favorable to the concentration and precipitation of metallic minerals from their solutions, The direction of the veins is generally between Northeast and Northwest, or East and West; their dips are steep or vertical.

The quartz of the pegmatite gangue, when impregnated with telluride ore, °° a pale, bluish-gray and rather greasy appearance, streaked here and there with a dull, blackish, greasy stain, upon which sometimes the true telluride minerals such as sylvanite, can be seen, generally inlong thin crystals of a bright tin-like appearance. It is sometimes called graphic tellurium, because the crystals crossing one another assume <he form of Hebrew characters. Sylvanite is a telluride of siiver and gold. There are many varieties of telluride, some rich in silver and others in gold, and some with both combined. When a piece of gangue containing tellurium is roasted, the gold comes out in good sized globules on the surface.

Twogreat mother-veins, called the Maxwell and Hoosier veins, traverse the telluride district for several miles, easily traceable by theirrusty color. One carries pyritesand tellurides, the other silver ore and gray copper. Gold Hill district, in the telluride belt, is traversed by the Hoosier gangue. Several veins cross the Hoosier gangue and are richer in its vicinity ; in some, the ore isa telluride at the surface, but with depth passes down into gold-bearing pyrites.

The Ward district outside the telluride belt carries copper and iron pyrites bearing gold. Caribou is silver-bearing, its ores are galena, copper pyrites and zinc-blende occurring in gneiss near dyke of eruptive diabase. The No-Name vein crosses and faults the Caribou vein. Its ores carry both silver and gold; the ores are silver glance, brittle silver, gray copper, galena, copper pyrites, with native and ruby silver. The copper pyrites carries more gold than silver.

The granitic rocks near Boulder are thrown into a series of parallel folds, one series cut diagonally by another. The telluride veins run along the slopes of these folds. The veins are in cracks and fissures coinciding with this folding, some of the main fissures being filled at once by porphyry dykes, the others more gradually by vein material. The

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veins occur along, on, and near these dykes, along lines at the junction of the more massive granite with the bedded gneiss, along and between stratification planes of schist, and along the joint planes of granite. The veins are due to percolating alkaline waters dissolving metalliferous material and veinstone from the surrounding rocks, It is noteworthy that alkaline springs still exist in the neighborhood, as they do also at the mining district of Idaho Springs. The veins occur where the foldings are abrupt, and the direction of the veins is parallel to the strike of the stratification, As a rule the veins are not of great extent. A single vein can rarely be traced on the surface or beneath it for more then 600 feet. Before that distance is reached, the vein spi; off again into another.

Where veins cross at a small angle or where a spur branches off from the main vein, accumulation and enrichment of ore takes place. There are two courses of veins, one East and West, the other Northeast by Southwest ; the former system appears to be the older as the latter faults it.

The ore occurs in chimneys or pockets, with 4 good deal of barren ground between.

Small veins run parallel with each other for some distance, the interval filled with granite or pegmatite. Sometimes a vein pinches out entirely (contrary to the general habit of true large fissure veins occupying great fault fissures). The ore streak is from 1 to 20 inches wide containing more of this blue, greasy, fine grained "horn quartz" than the country rock. Some of the veins interlace ike arteries in a human body. Minute particles of pyrites (marcasite) often produce the dark stains we have noted on the telluride quartz. By moistening the stone, the telluride minerals and pyrite appear distinctly.

A Typical Boulder County Mine.

A good typical and very instructive example of a contact fissure, gold-bearing vein is that of the Golden Age at Jimtown, north of Boulder.

"At Jimtown a quartz-diorite dyke occurs, of light color containing much hornblende and titanic iron, running nearly through the street of the village. The cliffs at Jimtown, over 500 feet high, are of quartz porphyry, of white color, consisting mainly of large crystals of quartz and feldspar, set in a fine grained crystalline ground mass or paste.

Golden Age And Sentinel Veins,

From the town, the road winds up a steep mountain composed of coarse gray granite, with occasional belts of gneiss. Here are located the Golden Age and Sentinel mines,

The Golden Age covers the outcrop of a quartz-porphyry dyke cutting through the granite. This dyke varies in width, from a few 'eet to about fifty. The outcrop of the main ore chute of the Golden Age extends along the "contact'' on the lower side of the porphyry dyke. Ata depth of 100 feet the main shaft discloses a split in the vein. The hanging wall of the vein continues into the dyke, but with porphyry hanging and footwalls, until a depth of 330 feet, where it enters the upper contact between the porphyry and granite. The dyke has been much acted upon and decomposed by vein forming agencies in the upper workings, but in the lower it is less decomposed and shows considerable pyrites. The Golden Age veins are well defined, presenting a banded or ribbon structure. They are inclosed in distinct walls with gouge or selvages, which at times

show slickensides. The seams and feeders that have:

enriched both veins come in from the porphyry dyke.

The ore from the Golden Age contains rich and magnificent specimens of free gold. It isa free milling ore. When rich, the gangue is a hard, flinty, vitreous white quartz. The gold is seldom accompanied by pyrites. It is generally imbedded in the white quartz as bright yellow gold, in size, from coarse grains to nuggets several ounces in weight; after it reaches the lower contact between the porphyry and granite and enters the granite, there is an increase in the baser metals, such as zinc-blende, galena and pyrites, but the ore still retains its value in free gold.

Returning to the surface, 'he Sentinel location covers the apex of a vein, which there appears enclosed in a belt of schistose or gneissic rock.

This vein dips South at an angle of 70° and passes through the Golden Age vein on its course.

The Sentinel vein ore is entirely distinct from that of the Golden Age. It is the characteristic bluish horn quartz of the tellurium veins of Boulder County, with characteristic chalcedony quartz crystals and finely disseminated pyrites. The value is in metallic and such tellurium ores as petzite and sylvanite. Whilst most of the gold was deposited as native gold, a portion has evidently been rendered free by partial decomposition of the tellurides. This ore is very

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rich. The richest ore usually occurs in two narrow seams or streaks from a foot to ten feet apart, the intervening space being more or less mineralized country rock. It is richest when in the schistose rock, and poorest when it asses through the porphyry dyke. The crossing of the sentinel vein through that of the Golden Age is very clearly marked; it very slightly faults the Golden Age vein.

The gold mines of Boulder County belong to two distinct periods of vein formation; to one belong the non-telluride ores, and to the other those producing tellurium. The tellurium veins appear to be the later of the two.

The ores of the Sentinel tellurium vein are lower grade where the vein passes through the porphyry dyke. This is due to the Golden Age vein being formed first, and draining the dyke of its disseminated mineral values. The Sentinel received its mineral from the schistose or gneissic rocks, and is consequently richer where enclosed in those rocks than when in the dyke.

Plate Lxix.

Section of Gelden Age Vein, Jimtown, Boulder Co., Colo.

Prospectors look for richer or larger bodies of ore when veins unite or cross each other. In the Golden Age the two veins unite about roo feet below the surface. There are similar veins of the same age, and large and rich ore bodies are found at their junction. On the other hand, the Sentinel vein of later age, passing through the earlier Golden Age vein, produced no enrichment of the ore bodies,

To form such ore bodies, the veins should be of cortemporaneous origin."

The ore deposits of Gilpin and Clear Creek Counties are very similar to those of Roistiee, only they do not produce tellurium ores. The country rock is the same granite-gneiss, penetrated here and there by porphyry dykes. The pegmatitic veins are either in the gneiss or between the dykes and the granite. In some cases the porphyry dyke constitutes a vein in itself, such as the Minnie, which is a felsite porphyry, and the Cyclops, a quartz porphyry, In Gilpin county, around Central City, the ores are a mixture of copper pyrite and iron pyrite with a very little galena and zinc-blende, All are gold-bearing.

The richer ore occurs in streaks not over a foot wide, ina compact, fine grained mass of pyrite. Copper pyrite is richer than iron pyrite. The rest of the vein, often many feet wide, carries pyrite irregularly disseminated throug decomposed country rock. The bulk of these ores are difficult to treat, and are milled, the loss being 4o per cent. higher in the unoxidized ores than in the oxidized. The veins follow the cleavage planes of the gneiss, cutting the stratification planes at right angles with vertical dip. The porphyry dykes are older than the veins, as the cleavage planes intersect both the porphyry and gneissalike. Foran interval of 20 miles between these mining districts and the plains, there are no ore deposits of any importance known.

In Clear Creek County the ores are mainly silver-bearing ; the silver is derived mainly from galena and gray copper. Dykes of obsidian occur in one of the mines parallel with the vein, which is itself a porphyry dyke. The richest mineral is close to the obsidian dyke.

Fissure Veins In True Igneous Rocks,

Whilst most of our fissure veins and ore deposits generally are more or less associated with the Jresence of igneous rocks, there are some which are essentially zz igneous eruptive rocks alone.

The most remarkable of these are the fissure veins of the San Juan region in southwestern Colorado.

This region consists of an enormous plateau of lavas of great thickness resting upon and originally overflowing a a low mountain range or plateau of granitic and upturned sedimentary rocks, the latter representing most of the geologic periods from Cambrian to Tertiary. The:sickness

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Composed of a Succession of Lava Sheets Resting on Granite.

of these great lava flows, which were erupted about the Eocene period of the Tertiary, is upwards of 1,500 feet; this lava mass has been cut up by glacial and river action by profound canyons, into a rugged mountain range, the summits of some of the castellated mountains reaching a height of 14,000 feet above the sea. The lava sheets are also traversed toa depth of 1,500 feet more or less, by an extraordinary number of great quartz-fissure veins. These veins appear to fill shrinkage cracks resulting from the contraction on cooling of the lava sheets, strictly speaking they are rather "gash veins" on a larger scale than "true fissure veins," for they are mostly /¢mated to the thickness of the lava overflows and cease when they reach the underlying granite,

There appear to have been two principal eruptions; the first, during the early part of the Tertiary, covered the higher region of the San Juan mountains to a depth of 1,500 feet with an overflow of brecciated andesitic lava, which on cooling developed fissures of contraction traversing the lava mass in all directions ; these were subsequently and slowly filled with a hard bluish quartz containing more or less ore.

Following the first grand overflow were others of less magnitude, consisting of non-brecciated andesites and rhyolites. This second dynamic movement produced locally, fissures extending below the horizon of breccia into the stratified rocks. These, however,

are seldom productive below the eruptive zone, There are also metal deposits in connection with still older eruptions of andesite and diorite, such as Mineral Farm, Calliope, etc,

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Red Mountain.

In the Red Mountain district the ore deposits form a peculiar group. They occupy a series of more or less

connected irregular chambers, trending downward, probably channels of ancient hot mineral springs. The nth Soares water completely silicified the surrounding eruptive rock for some distance away from the ore chambers. So the ore bodies are distributed through a huge irregular column of quartz extending to an undetermined depth. Large masses of brilliantly colored .aaterial are conspicuous in this region, They have been acted upon by mineral waters circulating through their crannies and fissures, Ore bodies are occasionally found in these and such mines are locally known as cave mines. The ores of the San Juan are mostly argentiferous gray copper, copper pyrites and galena associated with zincblende and iron pyrites in usually hard horn-quartz matrix. Some of the ore locally contains a high per centage of bismuth; others produce pyrargyrite and polybasite, rich silver minerals; others carry considerable gold, such as the recently discovered gold belt at Ouray. This belt occurs in Dakotah Cretaceous sandstone, which has been altered into a quartzite by the intrusion of dykes and sheets of eruptive diorite. One of these sheets spreads out in the quartzite. The ore occurs at the top of the quartzite, at its junction with a bed of shale. The gold, which is free and enclosed in brown oxide of iron, doubtless originated from the porphyry, and entered the joints and bedding planes of the quartzite, where they were opened by faulting. Above the shale the ore does not penetrate, the shale acting as an impervious resistance to uprising solutions, Ore bodies also occur in the Jurassic limestones below the quartzite, especially where they are penetrated by eruptive rocks. In the eastern portion of the San Juan region some important gold deposits occur near Del Norte in the Little Annie or Bowen Mine, which appear to be a decomposed dyke of eruptive rock, containing free gold in brown iron, in the upper portion, and with depth iron pyrites also goldbearing.

Creede.,

At the newly discovered camp of Creede, not very far from Del Norte, the fissure veins are very similar in character to those elsewhere in San Juan; they are quartz fissure veins traversing andesitic breccia and other volcanic rocks. The gangue matter in thes' veins is exceedingly rich in silver-bearing ore, so much so that the amethystine quartz composing the gangue or veinstone is quite in a

minority to the ore, and the vein may be said to be nearly a mass of ore from wall to wall, The thick lavas of Creede rest doubtless with depth upon Carboniferous limestone or else on bare granite; the former is found outcropping at some distance trom Creede, from beneath the lava overflow, and being penetrated by intrusive eruptive rocks shows signs here and there of productive ore deposits similar probably to those at Leadville. Creede is an encouraging example to a prospector, that all productive veins in Colorado have not been discovered yet, even in districts that have been pretty well tramped over, Creede had doubtless often been more or less walked over by prospectors for vears before the great discovery was made, and ina year's time we may hear of several more similar discoveries in the great San Juan,

Rosita And Silver Cliff.

The next important and peculiar igneous district carrying fissure veins is that of Rosita and Silver Cliff in the Wet Mountain Valley near the edge of the prairie country in southeastern Colorado, Here a local eruption of considerable power and magnitude and of comparatively recent date has occurred, These eruptions, consisting of andesitic, rhyolitic and trachytic material have built up cones and rounded hills largely of fragmental material such as consoli-

dated tuffs, ashes, and breccia, all of which, as at Cripple

Creek, rest on granitic basement rock. From the fragmentary character of the rocks it is evident that most of the eruptions were explosive, alternating, however, with quieter flows; in some cases the dykes can be seen, where some of the lava came, at others the "necks" or throats of the volcanoes themselves filled up with volcanic boulders; of such is the celebrated Bassick Mine. The mine is in the throat of ar old crater of andesite, filled with boulders of granite and andesite bedded in gravel and sand. The ore of the Bassick appears as concentric zones or shells around these boulders, as a replacement of the gravelly matrix. The entire mass has been permeated by heated waters which have decomposed the rocky fragments, depositing opaline quartz and kaolin in abundance,

The concentric shells around the boulders carry alternately several minerals,such as galena,antimony, zinc-blende, copper and iron pyrites, all more or less gold-bearing. The ore deposition in this region seems to have taken place at the close of the eruptive period, when the eruptions were

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dying out into hot springs, fumaroles, etc., and producing great decomposition of the lava rocks. The district was not thought much of, until Mr. Bassick made his discovery in the unpromising looking throat of the old volcano, containing a formation quite anomalous, and which the regular prospector, -accustomed to true, orthodox fissure veins, would have passed by as very unlikely. So it may happen to future prospectors, that some very unlikely formations may turn out great riches; hence it is well to keep a sharp lookout for everything examinable.

A STUDY OF MODERN LIVING VOLCANOES TO UNDERSTAND THE CRIPPLE CREEK VOLCANO.

By far the most typical, instructive and important gold camp in Colorado and the West is that of Cripple Creek. To

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Plate Lxxii.

Stromboli Volcano.

understand the geology of the Cripple Creek region and gold-bearing volcanic regions and rocks and their relations to the ore-deposits, a knowledge of the phenomena attending modern volcanic eruptions is necessary. Letus take that of the living volcano of Stromboli, described by Professor Judd, as throwing some light on the phenomena that may have occurred many thousands of years ago in the now extinct volcano of the Cripple Creek district.

From a point on the sides of the mountain of Stromboli, masses of vapor issue and unite to forma cloud over the mountain. This cloud is made up of globular masses, each of which is the product of a distinct outburst of the volcanic forces. At night a glow of red light appears on the cloud, increasing gradually in intensity, and as gradually fading away.

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After an interval this is repeated and continues till the light of dawn causes it to be no longer visible. When we land on the island we find it built up of the "ejecta" from the volcano like a gigantic iron furnace with its heaps of cinders and masses of slag. The irregular shape and surface: of the island is due to erosion removing the loose materials: at some points, and leaving the hard slaggy masses standing up prominently as dykes and hard portions of lava flows, as. Pisgah, Rhyolite Mt. and others at Cripple Creek do, above the eroded and more fragmentary tuffs and breccias. This. great heap of cinders and slags rises 6,000 feet above the sea bottom with a base four miles in diameter; 2,000 feet above: sea level is a circular depression, the crater of the active: volcano,

Looking down into the crater, an outburst takes place.. Before the outburst, many light curling wreaths of vapor ascend from fissures on the sides and bottom of the crater..

Possibly this is the origin of some of the dyke-filled fissures:

of Cripple Creek. Suddenly a sound is heard like a locomotive blowing off its steam. A great volume of watery vapor is thrown up into the atmosphere, and with it a number of dark fragments are hurled 500 feet above the crater, some fall- aS

ing on the mountain, KS f SRO others back into the ORY ) a crater with a loud can ae rattling noise. Those X rolling down the mountain are still hot and semi-molten. This is a clue to the origin of the fragmentary materials composing the tuffs and! breccias at Cripple Creek. The black slaggy bottom of the: crater is, as we have said, traversed by many fissures emitting jets of vapor. Some of these are quite large and vary in size and number and position at different periods. From. some, only steam is emitted in loud snorting puffs. Im others molten material is seen welling up and flowing out-

PLATE LXXIII. Map of Island of Stromboli.

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side the crater. Such fissures when all eruption has ceased would be found, as at Cripple Creek, sealed up with solid

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Plate Lxxiv.

Stromboli Crater.

lava with a lava flow on their tops. From this liquid mass, steam escapes in considerable quantities. Within the walls of the fissures, a viscid semi-liquid 'ave heaves up and down and churns around till at last a gig. 1tic bubble or blister is formed which bursts violently and a great rush of steam takes place carrying fragments of the scum-like surface of the liquid high into the air. At night the fissures glow with ruddy light. The liquid matter is white hot and the scum on ita dull red. Every time a bubble bursts a fresh glowing surface is exposed. It is the reception of this upon the clouds of steam above the mountain that causes the fitful glows of light we mentioned.

The phenomena show there are cracks communicating with the earth's AW interior highly heated matter beneath the surface, together with great Wer eaeand Tul in the quantities of impris-

oned water, which escaping as steam give rise to all the active phenomena.

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What is popularly supposed to be flame in an eruption is the reflection on the cloud of steam and dust, from glowing masses in the mouth of the crater. Sulphur is not, as commonly supposed, erupted from a volcano, but is formed by the union of sulphurous acid and sulphureted hydrogen issuing from vulcanic vents.

A volcano is a steam vent, like a geyser, which may be called a water volcano.

Origin Of Fissures,

Some light is thrown on the possible origin of some of the Cripple Creek dykes and fissures by the eruption of Vesuvius in 1872. The bottom of the crater was entirely broken up and the sides of the mountain rent by fissures in all directions. So numerous were these fissures that liquid matter appeared to be oozing from every part of its surface and the mountain to be "sweating fire.' One fissure was enormous, extending from the summit to far beyond the base of thecone, This, filled witha dyke of lava, is visible to-day. From both crater and fissures enormous volumes of steam rushed out with a prodigious roar. This roaring was from explosion of bubbles one after another, and the vaporcloud above Vesuvius, as at Stromboli, was made up of globular masses of steam ejected at successive explosions. Each explosion carried upward quantities of fragments which fell 2: back on the mountain. All along the course of the stream Hi of lava, volumes of steam were thrown off.

Origin Of Tuffs.

The discharge of such large quantities of steam causes the atmosphere to be saturated with watery vapor, which, condensing, falls in excessive rain storms, producing mud streams formed by rain water sweeping along the loose vol- 4 canic dust and debris. In some such way, doubtless, the Cripple Creek tuffs and breccias were formed.

Gases And Materials Ejected From Volcanoes,

The most abundant of the substances ejected from volcanoes is steam, and wiih it many volatile materials, such as hydrochloric acid and carbonic acid, also hydrogen, nitrogen and ammonia, and at Cripple Creek fluorine gas.

These different gases at Cripple Creek had much to do with the formation of ore deposits. Volatile metals, such as

arsenic, antimony and cinnabar are erupted; these sub- 'stances, issuing from volcanic vents at high temperature, react upon one another forming new compounds, such as 'sulphur. Hydrochloric acid unites with the iron in the rocks to form yellow ferric chloride, common at Cripple Creek, and looking like a greenish yellow sulphur. Acid

Plan

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Plate Lxxvi.

Plan and Cross-Section of the ™ of a Crater. Black=Dykes Filling Fissures.

-gases change lime, alkaline and iron elements into sulphates, chlorides, carbonates and borates, which, when removed by rain, leave a white substance like chalk, composed of pure 'silica. Beds of such material occur not far from Cripple 'Creek and powdered silica in some of the mines.

The lips of fissures from which steam and gases issue are 'coated with yellow and red incrustations of sulphide and oxide of iron, such as are common in many prospect holes aat Cripple Creek.

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Solid materials are ejected in vast quantities; fragments of the rock masses through which the fissure is rent are

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Microscopic Structure of Some Crystals Showing Microlites and Crystallites.

Plate Lxxvii.

carried upwards by the steam blast, together with other matters far beneath the surface in a semi-fluid condition. Hence it is that at Cripple Creek we occasionally find

fragments of red granite imbedded in the volcanic breccia torn from the throat of the volcano in its passage through the underlying granite of the region.

Mineral And Chemical Elements Of Lavas.

Eight chemical elements make up the mass of lavas, oxygen, silicon, aluminum, magnesium, calcium, iron, sodium and potassium. Oxygen makes up the larger proportion so that lavas are mostly oxides. Next is silicon and aluminum, giving the quartz and feldspar and silicate element.

Lavas are of two kinds, acidic and basic. Acid lavas contain eighty per cent. silica, basic forty-five per cent. The former are rich in potash and soda, the latter in lime and iron; the former are commonly light in color and weight, the latter dark and heavy. Rhyolite is an example of an acidic lava, basalt of a basic one. The andesites and phonolites ot Cripple Creek are intermediate, The minerals composing these lavas are principally quartz and feldspar, together with the dark minerals, mica, augite, hornblende, olivine and magnetite.

Crystals And Microscopy Of Lava.

Many lavas are of a glassy nature, others contain many crystals, some of large size.

Microscopic sections of lavas show them to be made up of a ground mass of a glassy character, with distinct crystals set in it like plums ina pudding.

In others, the crystals are so thick that the glassy base can scarcely be seen.

Through the midst of the glass, cloudy matter is observed ; a higher power shows this "nebula" to be comp sed of minute particles called crystallites, the embryonic forms of crystals. Sometimes we can see an attempt of these particles to aggregate into a geometrical form, sketching out the outline of the large crystal they intended to form, but were prevented from finishing, by the cooling of the glassy magma. These crystallites assume forms like ferns, hairs, Spiders, etc.

In subterranean regions the conditions were particularly favorable for the development of crystals. The lavas cooled with extreme slowness, under enormous pressure, allowing plenty of time for the crystals to form.

Those lavas containing most soda and potash (acid lavas) assume a glassy condition, and these have often cooled near

the surface rapidly, the more crystalline varieties slowly at great depth. Obsidian and rhyolites are glassy types, granite and some porphyries with large crystals are of the latter class, whilst andesite and phonolite may be intermediate. The latter, however, at Cripple Creek, may have cooled quickly near the surface, and the crystals are for the most part small.

Besides the natural imprisoned water, crystals in lavas are found microscopically to contain globules, sometimes filled

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Plate Lxxviii.

Minute Cavities Containing Liquids in the Crystals of Rock.

with gas, salt, and water, which may add to the materials for the production of steam.

Eruptions Of Dust.

Steam escapes from lava so violently that the froth or scum Called scoria, is broken up and scattered in all directions. This scoria like pumice is full of little holes like a sponge, due to escape of the steam in it. Such spongy scoria is found scattered over the hills of Cripple Creek. During violent eruptions a continuous upward discharge of these fragments is maintained ; the cindery masses hurtling one another in the air, fall back into the vent, or are scattered over the mountain. Being often shot up again and again from the vent, they are reduced to the finest impalpable dust. They fill the atmosphere to such an extent as to bring on an " Egyptian darkness." This dust, mingling with descending rain, forms destructive mudflows, and sets or consolidates into the tufas or tuffs so abundant at Cripple Creek. When larger angular fragments are caught up and

consolidated with these, the rock so formed is a breccia, as already illustrated.

Volcanic craters after having been formed, are liable to be disturbed by later eruptions, Thus the crater of Vesuvius was reduced 400 feet by a later eruption, the old crater blown up and a much vaster crater opened.

Cripple Creek also witnessed its second disturbance, after the andestic eruption had ceased, by one of phonolite lava.

Fluidity And Other Properties Of Lavas,

Some lavas, such as basalt, are reduced to such a state of fluidity that their streams run like water to great distances, Others are of a more viscid, mortar-like consistence, especially the acid lavas, such as those of Cripple Creek. These are apt to flow but a short distance from their source, and to build up big domes and thick masses; of such a nature seems the structure of Nipple Mountain, south of Cripple Creek.

The peculiar columnar structure often observed in basaltic lava sheets, and in a rough way developed in the phonolite of the cliff above Victor mine, is due to cooling Sad cont taG. tion somewhat in the same way as mud cracks are formed in a drying up pond. A block of lava isolated by these cracks assumes a polygonal form like the basaltic columns of the Giants Causeway.

During the cooling down of lava and the escape of steam and gases, deposits of sulphur, specular iron and (at Cripple Creek) fluorspar, are deposited. Specular or micaceous iron is not uncommon at Cripple Creek. Rock masses are completely disguised by these incrustations.

Stratification Of Tuffs,

Tuffs and breccias are often found stratified. The fraginentary materials in falling through the air are sorted, the finer particles being carried farther from the vent than the larger ones. Craters built up of tuffs and breccias fallen in the condition of a muddy paste, show very fine stratification.

Large cones are built up of uniformly spread layers of more or less finely divided material disposed in parallel succession. At Cripple Creek the bedding is indistinct, and often difficult to trace, the dip of stratification being still more compressed by the cross fracturing of the rocks; hence it is hard to tell whether the lines represent cross

fracture cleavage, or bedding planes. In most volcanoes the stratified tuffs are cut and crossed, as at Cripple Creek, by numerous dykes running in various directions, cracks filled by lava from below.

Movements, too, have taken place subsequent to t 1e accumulation and consolidation of the whole material as shown in Plate LX XIX, whereby the masses are faulted and fresh fissures opened in them, Faults are found in some of the mines at Cripple Creek, faviting not only the lavas, but the veins also, Cliff sections of volcanoes show alternate beds of solid lava, scoria and tuff, representing different eruptions or flows,

There seems an order and succession in the eruption of the different varieties of lava. During the earlier periods

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Plate Lxxix.

Cliff Section, Composed of Alternate Beds of Lava and Scoria, Cut by Lava Dykes, and Faulted,

rhyolites, andesites and phonolites are erupted, and later basalts. This appears to be the case in the volcanic region west of Cripple Creek around Mt. MacIntyre, Thirty-Nine Mile Mt., and Black Mt. The prevalence of basalt capping the other lavas in that region, together with the greater freshness of the rocks, imply that its eruptions were somewhat later than those of Cripple Creek where basalt is not found, and where the rocks are much decomposed.

Volcanic eruptions shift their centers from time to time, making new cones along a line of fissure (for volcanoes are built upon lines of fissure). See Plate LXXX. Extinct craters are frequently filled by beautiful deep lakes. Cones rise within cones, and within great crater rings. At each

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successive great eruption, the old cone is blown away, and a new one formed,

Hot springs domain large quantities of silica or quartz in solution, The solution of silica is effected at the moment of its separation from combination with the alkali during the decomposition of volcanic rocks, and is favored by the presence of alkaline carbonates in the water, high temperature, and the pressure under which it exists in subterranean regions. When the water reaches the surface and is relieved from pressure and begins to cool, silica is deposited. So are the basins of geysers formed, and so the opal and hydrated quartz we find in many of the Cripple Creek veins, and in resilicated rocks,

Hot and cold springs rising in volcanic regions are charged with carbonic acid, and passing through calcareous

Plate Lxxx.

Showing Craters Found Along a Line of Fissure in the Eruption of Etna.

rocks dissolve large quantities of carbonate of lime, and redeposit it in a crystalline form known as "travertine." Near the base of Mt. MacIntyre, west of Cripple Creek, a prospect is opened on a fissure filled with this substance. Nearly all eruptions take place along lines of fissures (See Plate LXXX). Probably all volcanoes are located upon fissures of some kind, and even the general distribution of volcanoes over the earth's surface has been attributed to lines of fissures, as if the earth had been cracked like a glass globe. We have plenty of opportunities of seeing ancient fissures filled with lava in the numerous dykes at Cripple Creek, and in the greater volcanic region west of it; but so far no distinct volcanic craters have been found. Nevertheless it is probable that craters existed along these fissures, long since removed by erosion, or buried deep under flows and surface matter. We not unfrequently find at Cripple Creek that fissures did not all succeed in breaking through to the surface, for at some depths in the mines the apices of buried

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dykes are found and fissures filled by vein matter, whose outcrops do not appear at the surface. A single vein is followed from the surface and with depth two or more veins are often encountered, together with various small fissures.

Earthquakes doubtless accompanied the eruptions, and developed many smaller fissures, and turther shattered the rocks. Added to this at Cripple Creek, there was the second eruption of phonolite, alter the andesite had ceased. This second eruption doubtless added new fissures in the efforts of imprisoned vapors to force for themselves channels to tne surface,

Gases And Solfa'Ttaric Action,

The several stages in the decline of each volcanic outburst are marked by the appearance at the vent of certain acid gases. As the temperature at the vent declines, the nature of the volatile substances emitted undergoes a regular series of changes.

In fumaroles, sulphurous acid and hydrochloric acid abound, with sulphureted hydrogen and carbonic acid in much smaller proportions. Around these fumaroles, deposits of sulphide of arsenic, chloride of iron and of ammonia, boracic acid, and sulphur take place. Arsenical pyrites are a common associate for the ores near the surface at Cripple Creek, and many rocks are permeated with iron pyrites.

Where a volcanic vent sinks into extinction, hydrochloric and sulphurous acids are first evolved, and later sulphureted hydrogen and carbonic acid springs. Such springs are common in the volcanic districts of Colorado to-day, but we have long passed the stage of the stronger acids, which could only be expected in the pit of an active modern volcano like Kilauea. We may, however, expect to find traces left of these gases, in the rocks of Cripple Creek, such as a bleaching and decoloration of the rocks, leaching and precipitation of iron, forming those varied patterns of oxidation so common at every prospect hole; also deposits of various sulphates and chlorides, rocks deprived of iron and alkalies reduced to powdery siliceous masses,

One: -tion of subterranean springs is the transportation of material in a state of solution and redepositing of it elsewhere, especially in lines of relief of pressure, such as fissures, shattered rocks, and decomposed rocks and zones in the rocks.

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At Steamboat Springs, Nevada, metallic gold, cinnabar and other minerals have been found coating the sides of fissures from which living hot springs issue at the surface, In great volcanic foci the transfer of various sulphides, oxides and salts, which fill veins, has been effected either by solution or sublimation, or the action of powerful currents. This applies to the veins and ore deposits in question,

As the igneous activity of a district declines, the temyerature of the issuing gases and waters diminishes, till at ast the volcanic forces appear to have wholly abandoued the region and been transferred to another, This may have been the case with Cripple Creek and the volcanic region west of it, of apparently later date. The history of a volcanic disturbance is as follows:

First. The area is troubled by subterranean shocks and earthquakes.

Second The origination of fissures is indicated by the appearance on the surface of hot and carbonic acid springs and other gases,

Third. With increased subterranean activity the temperature of the springs and gases increases,

Fourth. A visible rent is formed at the surface.

Fifth. From this fissure, gas and imprisoned vapor escapes so violently as to disperse the lava in clouds of scoria or dust, or to cause it to well out in flows.

Sixth. Volcanic action concentrates at one or several points, and the ejected material accumulates from volcanic cones.

Sometimes the volcanic activity dies out entirely, leaving cones thrown up along the line of fissure. At others, some such center becomes for a long time the habitual vent for the volcanic forces of the district, and a large cone is built up.

When the height and thickness of the cone have grown great, the succeeding eruption rends the sides of the cone, producing fissures, quickly filled by 'ava, forming radiating dykes and surmounted by parasitic cones. The dykes of "ny le Creek may in cases represent such occurrences.

hen volcanic energies can no longer raise material to the summit of the crater, nor rend the sides, they find relief by making new fissures and small cones in the country outside the main volcanic crater. The numerous phonolitic dykes in the granitic region outside of the main center at Cripple Creek may have so originated. At last volcanic energy diminishes, eruptions of lava cease, fissures are sealed up with solid lava, volcanic cones crumble away.

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But still the existence of heated matter at no great deptfn is indicated by outbursts of gases and vapor, formation of geysers, mud volcanoes and hot springs, As the underlying rocks cool down, the issuing jets of gas and vapor lose their high temperature, diminish in quantity, geysers and mud volcanoes become extinct, hot springs disappear, and all is quiet,

It was in the latter or hot spring stage, that the ores were at Cripple Creek leached from the volcanic rocks, probably from great depths as well possibly as from the sides, and concentrated and deposited in the fissures, shattered zones,, and decomposed rocks, The last stage is as we find things. to-day.

GENERAL SUMMARY OF PROBABLE VOLCANIC EVENTS THA'L OCCURRED AT CRIPPLE CREEK,

At Cripple Creek there was a volcanic eruption in Tertiary times due probably to some mountain elevation going on in the region of Pike's Peak or generally in the mountains,

We may assume that preluding the eruption the area was. troubled by earthquakes. Various kinds of acid and hot springs appeared above the surface, indicating the fissuring of the ground that followed.

At the bottom of these fractures, which may have beem numerous, molten rock appeared, giving off imprisoned vapor from bursting blisters of lava, These shoots of steam: formed into a cloud overshadowing the area, and carried upwards quantities of scoria and fragments, which fell back around the orifices, forming crater cone, or craters. These fragments being repeated si ot up, and falling back into the crater were comminuted into fine dust, and fell, together with larger angular fragments, over the surface.

The atmosphere charged w.*h condensing steam gave riseto heavy rain falls. The witer descending the ravines, caught up the volcanic dust and fragments, forming mud-- flows, the materia! rapidly setting into the rocks we call tuffs and breccias.

As the first eruption at Cripple Creek was of andesite, these are called andesitic tuffs and breccias, and constitute the principal mineralized rock of the mining area.

These tuffs are sometimes stratified by the materials being sorted in the air by the water.

After this first eruption ceased, there may have been a

rest for a time, the lavas may have cooled and consolidated, and the region been covered by various acid and hot springs, issuing from fissures caused by the late eruption.

Then the district was a second time disturbed, this time by an eruption of phonolite, ascending through numerous rents and fissures, not only in the overlying andesite, but also in the granitic region outside of the first volcanic "focus," probably finding the old seat of action too much choked by eruptive matter.

This second eruption added many new fissures to the already shattered rocks, and gave many opportunities for the deposition of metallic and vein material deposited through the medium of vaseous and hot spring and solfataric action which followea upon the cessation of the phonolite eruption.

After the eruptions at Cripple Creek ceased the volcanic forces seem to have transferred their field of action to the area west of Cripple Creek in the Four-mile district. The rest is the history of to-day.

Cripple Creek As A Prospecting Field.

A visitor standing on top of one of the hills like Mt. Pisgah, overlooking Cripple Creek, and glancing at the various mines and multitudinous prospect holes speckling the hills, is struck with the compactness of the mining district within the limited area of 18 square miles. In this small area all the principal mines are located, and one can ride around the entire camp in an hour or two. Outside of this area, there are as yet no mines of importance, though prospect holes may be found for a circuit of many miles.

Andesitic And Granite Areas,

He will observe that the principal mines are located on the round smooth hills, on their tops, slopes and on the gulches, where the vegetation is mostly grass and quaking aspen. These too are within a sort of natural rampart of more rugged hills wooded with pine. In these outlying hills, only a few scattered prospects are visible. The reason for this is to be found in the geology of the region, and the differences between the areas occupied by andesitic breccia and granite. The rounded grassy aspen-covered hills representing the andesitic breccia carry most of the ore bodies, and the principal mines are restricted to them, The

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SALA Ke ae SCOT Cm

more rugged hills, covered with fir trees, represent the granite area, and in them for the most part are few mines of importance, though many likely prospects are opened upon dykes of phonolite, which, so far as known, does ne' as a rule seem to be so productive a rock as the andesite.

There are intermediate areas, such as that of Battle Mt., characterized by the presence of both andesitic breccia, phonolite dykes, and granite, in which are some of the richest mines of the district, such as the Independence, Portland, Annie Lee and others.

It will appear how important and useful a geological survey is of such a region, a fact not always recognized by practical miners. If the ore bodies are mainly associated with the particular rock called andesitic breccia, it is well for them to be able to recognize that rock, and ascertain the limits of its area,

Signs That Lead To Prospecting,

The next thing that strikes the observer, is the prodigious amount of prospecting holes and prospecting trenches, the latter being particularly common. He may ask, what was there in the general appearance and character of this district that led the "eagle eyed"' prospector to suspect the existence of ore bodies in it, or that it was "a kind'er likely looking place"? Again, how is it that it was so long overlooked by the "eagle eyed," especially when so easily accessible ?

On general principles, in past years, miners in Colorado, after the Leadville and Aspen excitement, were more on the lookout for silver than gold; they looked therefore for rocks like those of Leadville, with contacts between porphyry and limestone, and every limestone ledge in the country was ransacked. Silver was rarely found in volcanic lava rocks, except perhaps in the great San Juan region, and miners thought as little about prospecting unpromising looking hills of lava, as they would the basaltic caps of the table mountains on the plains. Again, gold leads do not show their ore on the surface like some silver-lead veins. There is nothing perhaps but a little seam of rust that might occur almost anywhere, and in any kind of rock, Hence lava districts of somewhat recent origin, were overlooked, rather than looked over. The discovery of the gold-bearing properties of the Cripple Creek lavas, together with the increased thirst for gold, turned the tables, and

Dah nen iat ee gel ec

Lin Ere Ete

mow throughout Colorado, every lava formation is being rprospected with as much zeal and indiscriminateness, as were the limestones in the Leadville days. bg ytd wae ad inaw needs to know volcanic lavas at sight, to distinguish varieties, and to know all he possibly can about their -origin, varieties and mode of occurrence. Hence the im- |portance we gave to the subject in the preceeding remarks .on volcanoes. prospector zow would at a glance con- -sider tthe area about Soe Creek as worth looking over; -and the geologist would consider it a very ain place, not merely from the presence of the lavas, but mainly from the -great decomposition of the rocks, and the evidence of the presence of past solfataric action.

Difficulties In Prospecting.

"But the "eagle eyed" one did not entirely overlook this district in the past, for some years ago he was sufficiently prepossessed with the appearance of things to drive a -couple of short tunnels in Arequa guich, and narrowly escaped becoming a millionaire. What troubled the prospector was, that though he found the hills covered with an extraordinary amount of "float," he could not trace this float to any ledge or rocks "in place." For the most part the hills were grassed over, or covered with vegetation ; and through the turf were very few outcroppings of a likely 'kind, so far as he could see. There were no prominent "quartz veins, or zones deeply impregnated with iron, hence she gave up the region, mentally wondering where on earth call this rich float could have come from, perhaps solacing this mind by one of his igneous, brimstony theories that it had been scattered over the country from a distant volcano, or washed there by flood or glaciers from some unknown distant region. The former theory after all was not far from the truth but the absence of all rounding and smoothing of the fragments of float precludes the latter hypothesis. Evidences of former glaciation are ramen katy absent from the vicinity.

The Region Impregnated With Ore,

'To those who have studied Cripple Creek of to-day, the source of this "float" is no mystery. Little, if any of it, has been broken off from orthodox quartz fissure veins, or even extracted from well defined ore zones. The fact is,

that the whole andesitic area is more or less impregnated with the precious metals, and the float on the surface is little more than the surface debris of the general underlying rock. There is scarcely a stone that you may kick with your foot over the entire area, but what will show some trace of gold, On one hill an experienced mining superintendent told me, that for an experiment, he went around with a wagon and picked up the "float" almost at haphazard, and it averaged 22 dollars in gold. That such a "floaty " region should receive attention some day is not to be wondered at, and we believe Colorado Springs men were amongst the first to give it serious attention by opening holes and prospecting trenches almost at random, resulting in important discoveries. Asa rule even after this, the best mines were discovered by mere chance and guess work, or by plodding but blind prospecting, something like the Leadville prospector who in early days had all Leadville before him to prospect, but did not know where to begin, till sitting down under a tree eating his lunch, he saw a squirrel scratching in the ground; he accepted the happy omen and "went down," so the story goes, and 0° course "struck it rich;"" so we understand the Pharmacist

and many other now noted mines were discovered at Cripple Creek.

Mode Of Prospecting,

This absence of surface outcrops or visible leads, when the "rush" came, led to indiscriminate and abundant prospecting which has been kept up till the present time, hence, the extraordinary freckling of the hills with prospect holes and trenches.

Sometimes they would select any piece of land they thought, for some reason or other or without any reason at all, likely, and go to work to punch holes and dig trenches all over it to find something. In this way they frequently came across enough signs to warrant putting down a prospect hole, and holding the claim and then went on "to pastures new."

Character Of Float And Other Surface Signs.

As we have said, the whole region is covered with float.

This float is usually a somewhat porous piece of lava, or

andesitic breccia, or tuff, stained with yellow, brown, or red oxide of iron, sometimes in patterns or concentric rings, It

ns

Tees

Ses

is often found to be honeycombed when broken with a hammer. There is no visible ore, but an assay will most likely show traces of more or less gold. Again, a species ot

pee ae

PLATE LXXXI] Prospectors Opening a Prospect in a New Reg:on West of Cripple Creek.

wih edhe titties

red porphyritic granite has been desilicated and robbed of many of its crystal constituents, and left as a porous skeleton of a rock by the action of gases and springs. The pores in this are often occupied by oxide of iron, or even by crystais

atetnalestisnnereareara ancumains rity tamer nantes gs

b

of fluorspar, This isa likely kind of float. Honeycombed rusty rock with quartz crystals isalikely float, both of these representing the action of mineral hot springs. At rare intervals we may see a little of this oxidized rusty rock in place protruding from under the grass, and if so, there is sure to be a prospect hole alongside of it.

Bold outcrops of lava rock are comparatively scarce and when they do appear, as in the cliff above Victor mine, Mt. Pisgah, Bahr, and Rhyolite peaks, the rock is apt to be so hard as to preclude the probability of much ore deposits in it.

Pieces of rock or float stained a violet purple color by fluorine are considered a good sign of an ore body not far off, this fluorspar being found characteristic of some of the richest veins in the camp; and fluorine gas was doubtless connected with the deposits of ore matter, especially of tne tellurium, the present matrix of the gold in the deeper parts of the mines.

Pyrites is not usually found on the surface till the rock is broken open, and tellurium in little silver scales and spots, not till considerable depth is attained. But free gold may be found in surface float, and from the grass roots down, and in the early development of a mine, in the oxidized upper portions, associated with iron oxide and black manganese or " psilomelane."

Micaceous or specular iron, is seen in some prospect holes; and localities marked by evidences of past hot spring action, such as the appearance of botryoidal chalcedony or opal should be prospected. A commonand curious marking in some of the bleached volcanic lavas is that of an imitation of trees, ferns and mosses, popularly called " photographic rock," scientifically " dendrite " or tree rock.

This remarkable imitation of nature is due to crystallization of solutions of manganese, and may be compared to fern-like appearances on a frosty window-pane in winter, which are certainly not of organic origin, or in anyway connected with the processes of photography. These dendritic markings may or may not be considered as signs of ore. Similar markings are very common in the porphyries of Leadville overlying the silver deposits.

Surface Prospecting Of A Mine.

In some of the surface discoveries of mines, when a considerable area, covered by a blow-out of iron oxide as-

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if G:

mn

if

Biz

sociated or net with purple fluorspar, has been found to run well in free gold, the ground is prospected and developed to the depth of a few feet, and over a certain area, with pews and scrapers, the material so obtained being sent wholesale to the stamp=mill and often giving rich returns. The object of this work ms not merely to get all the values out of this rich float, but in hopes of uncovering the vein or veins of which it is the oxidized cap or blossom. This was the way in which the Deerhorn mine was opened up, and its veins discovered on Summit Hill, The ground on the top of the hill is observed to have been "gophered"' in all directions like the catacombs to a depth of about 20 feet, and over an area of a square acre or so, This was done partly to gather up and collect the rich float which was found scattered over the hill and partly to discover the leads in place.

This rich float was stained with purple fluorine, and upwards of 25,000 dollars' worth of gold was obtained from this, the material being dug up by plows and scrapers, before the subsequently discovered veins were found or worked.

In the case of the Anaconda mine on Gold Hill, the outcrop of a dyke of andesite was discovered on the hillside covered with am oxidized crust carrying gold. The owners developed this by an open quarry, about a hundred feet in length and 4o to 50 feet deep, from which they extracted the bonanza which made this mine at its outset so celebrated, and later proceeded to uncover the dyke on the surface, to a depth of about 20 feet along the entire length of their claims, but nothing comparable with the bonanzas of the first quarry has been found since in extension or depth.

Richness With Depth, Etc.

Many of the mines shipped their best ore from the grass roots and upper oxidized portions of the veins, which contained free gold wand were free milling. With depth some of these mines have not done nearly as well, especially when they reached the unoxidized zone, away from surface influences, and the ore was found wrapped up in tellurium or iron pyrites.

The palmiest days of many a gold camp are its earliest days.

Suggestions 'To Prospectors.

In the more productive area the prospector will do well to keep to the andesitic breccia, and follow the sisis we

have mentioned, Outside of this area his course may be a little different, as then he isin the granite district, and looks out for the appearance of dykes of phonolite, rarely more than a few feet, though sometimes many yards, in width, and easily distinguished from the red granite by their light gray or white color, These dykes do not often appear outcropping in the granite cliffs, but are more commonly to be found buried beneath the debris and grass of the 'slopes. On these he may find no indication and trust to haphazard trenching; or a few stray pieces may lead him to the spot. The more rusty, oxidized and decomposed the phonolite, the more likely it is to carry gold; at times he may find ore

Plate Lxxxii.

ection Moose Mine Vein, Raven Hill, 1. Country Rock Breccia. 2, Yellow

Jasner, with Cavities of Quartz Crystals. 3. Blue Grey Jasper, with Seams

of 'Quartz and Iron containing Gold. and tree gold in the dyke itself, but more often at its contact, on one or both sides, with the granite. There he is likely to find a crevice filled with clay or iron-oxide, carrying seams and cavities lined with quartz crystals or stains of purple fluorspar,

Sometimes he may find the coarse granite, as in the case of the Independence mine on Battle Mt., just at the contact with the dyke of lava, to be very rotten, much honeycombed and robbed of many constituent minerals, and these, by replacement with metal, may yield him the richest ore, Again, the dyke between walls may be reduced to a blue or yellow jaspery clay, with a vertical lamination or cleavage, the lines of cleavage filled with quartz and iron oxide (See Plate LX XXII); in such lines he is apt to find the richest ore.

vs RRL SL NE ES TE 7 opemanenneracy

Aiter opening a prospect, the ore signs, consisting of stains of oxide of iron and manganese, instead of pursuing an even or regular course are apt to scatter amongst the infinite number of crevices shattering the rocks, no one little lead being of sufficient richness to follow with profit, and the whole body between walls scarcely paying to work.

The ore signs often follow a very uneven course, now lying upon a fairly defined wall, then running for a distance into one wall or other, or again following the main course of the creviced lava breccia between walls, now in pockets and crevices, again scattered, or again impregnating the porous and decomposed rock. There are very few true, well-defined veins in the camp; the ore rather impregnates certain ill-defined, shattered zones of rocks between certain ill-defined boundaries called walls. At others the ore occupies narrow Cleavage planes in the rock, of which there may be two or three in a mine, some of them productive, others very little so. Ore bodies in the harder or more compact rocks, such as the Buena Vista and Victor mines, are apt to have something more like defined veins and defined walls. In some cases surface signs have been poor, and with depth have done well; the exact opposite has often been the case. Some mines have been good from bottom to top, but we have to be careful here, as in most gold camps, of the old fallacy of "richness with depth." There is little more criterion for this than in other camps, and many a once famous mine is looking vainly with depth for its lost bonanza, though in other respects doing fairly well.

As regards the granite itself, we have heard of few ordinary quartz fissure veins unaccompanied by lava intrusions proving productive.

The fine grained, red, eruptive granite on Barnard Creek, north of Cripple Creek, has shown a promising ore body in a lava dyke in the granite, which, singularly enough, produces a fine grained galena, rich in gold. Galena is quite a rare ore in Cripple Creek. Green carbonate of copper stains appear at times in the schists and gneisses, but none so far productive.

The railroad from Canyon City to Cripple Creek did some good prospecting work in the granite area, its cuttings exposing quite a number of phonolite and other dykes, together with some granitic veins.

Outside of Cripple Creek, in the great volcanic area to the north, between Cripple Creek and South Park, is a fair prospecting field. The rocks are mainly granites, rhyolites,

trachytes, andesites and basalt, the products, as at Cripple Creek, of a series of volcanic SERDE EOE. of which the latest q appears to have been basalt, which commonly caps the fi other and lighter colored lavas,

The rocks in this region are for the most part less decomposed than those at Cripple Creek, which is not so favorable ee sign. Here the prospector should look out for all signs a

of decomposition, such as we observed at Freshwater district, a not unlikely spot. The very hard, massive rocks are not likely to be productive, such as the hard black basalts. The lighter colored and more decomposable lavas offer a better chance.

Centers of eruption, such as relics of old craters and dykes from which these different lavas issued, should be sought for and prospected. Balfour, a small mining camp at the north of this area, is established among granite and eruptive rocks, which have been found to be mineralized by pyrites. The granites here have several fissure veins and dykes in them, showing considerable disturbance to have taken place in that neighborhood. The low hills in which the prospect holes are located are capped with basalt, apparently resting on volcanic tuffs and other lavas. So far, nothing very productive has been found, though here, as elsewhere, much is hoped for with depth, Singularly enough, in one of these veins in lava, we noticed a tarry substance or inspissated bitum_n in the cavities of the rock, an unusual occurrence in fissure veins or in volcanic rock,

Chapter Xii. Ore Deposits In Sedimentary Rocks.

Blanket Ore Deposits, Contact Deposits,

This great second class of ore deposits, occurring principally in Paleozoic limestones at contact more or less with intrusive sheets of porphyry, is mainly represented in Colorado by the Leadville and South Park mining district, the Kokomo and Red Cliff districts, and the Aspen and Gunnison districts, though locally here and there, wherever Paleozoic strata accompanied by igneous rock may be exposed, silver mines may be found. We will begin with Leadville and South Park as primarily instructive and typical.

we LEIS NT 7

ees See

a NC EIEIO AS

South Park Ore Deposits,

The basin plain of South Park is underlaid by sedimentary rocks from the Cambrian below, to the Upper Cretaceous on top. These strata slope up to the crest of the Mosquito range on the west, where they become violently folded and faulted and eroded,

The mineral developments are on the slopes of this range on both sides of it.

The order of succession of strata forming the structure

Lime fl see S § Shale 000. SS i Black Shale pw SS SS spate °/ UT SS as Contact Deposit

ty Ss ™ "pe + ; SRL SGEOIS IL wartoPoronyey SRR hae PMO MYY Shale SSSSSSss8 Spe tl Lower Carboniferous " SSS Sen "Blue Limestone" & RLS S EERE OSS fares ng Quartzite f . te n A COO ERS Drab dotomitio Aki % pe oe cae gemestone hry Pts ADEN te 'ambrian

U iP : SSMS: SES Ses ez es Quartzite

PLATE LXXXIII. Section of Leadville Cliff.

and cliffs of the range and resting on the granite, 1s as follows, beginning with the lowest : Feet thick. Cambriat Quarvtste ss siiiccccdicecsccecesdiwecsvis ousneagencseest 200 Silurian drab limestone (dolomite) cscseeeeceeeeeeeeeenes 200

Lower Carboniferous blue limestone 0seeeeeeees eoeees 200 Middle Carboniferous sandstones and quartzite (Weber grits). .2,000 Upper Carboniferous limestones, reddish sandstones 1,000

PORES ies vera nee Bice oes users 3,600 to 4,000

These formations have been traversed by eruptive quartzporphyry and porphyrite dykes and intrusive sheets. The dykes occur principally in the Archzean, but the intrusive sheets are many and are spread out between the quartzites and limestones of the Cambrian, Silurian and Carboniferous.

The connection between the eruptive masses and deposition of ore ts very marked, The ore bodies are a concentration of the metallic minerals originally disseminated through the mass of these eruptive porphyries and deposited along their plane of contact with the sedimentary beds, and by metasomatic substitution extending more or less into the mass of the latter,

On mountains Lincoln and Bross, in the principal mines, the ores are mainly argentiferous, yielding galena and its products of decomposition, viz., carbonate of lead (cerussite) and sulphate of lead (anglesite) with chloride of silver, Barite (heavy spar) is a common gangue or veinstone especially in the richest parts of the mine. Iron pyrites decomposed and passing into a hydrated oxide of iron, together with a black oxide of manganese, give to the ore its rusty and black color.

The deposits occur in irregular bodies or pockets often of great size, in the blue limestone, near its upper surface, but not always easy to find or follow. This limestone was originally covered by a sheet of quartz-porphyry which has been locally removed from the ore deposits, but exists in the peak. This porphyry, generally recognized by its large feldspar crystals is called Mt. Lincoln porphyry and is quite common and characteristic of Western Colorado, In the Dolly Varden mine the ore occurs in the limestone at contact a vertical dyke of white quarts-porphyry.

In the Fanny Barrett mine, on Loveland Hill, rich deposits of galena and anglesite occur in a vertical fissure (probably a gash vein) crossing the hill from side to side and traversing the Paleozoic strata at right angles to their dip, but probably not entering into the underlying granite. This mine was discovered by eels little pieces of iron following a general line across the hill.

n Buckskin Gulch the Phillips mine is an immense mass of gold-bearing iron pyrites, deposited, in beds of Cambrian quartzite near a dyke of guartz-porphyry. This mine was discovered by its rusty outcrop being exposed along the edge of the stream. At first this crust of iron oxide was loose enough to be panned for gold with good success by the old timers, and afterward milled. But when the hard pyrite set in, the ore was found to be too low grade to pay for roasting and smelting, and for many years lay idle. The Criterion in the cliff above this consists of /arge caves in Cambrian quartzite, still partly occupied by oidized gold-bearing iron ore, and galena-bearing silver close to a porphyrite dyke.

ee

a ae RE GOL BOSAL

The London mine in Mosquito gulch is peculiar and instructive as being involved in the great London fault. There are two strong veins or deposits of pyrites carrying both gold and silver, the gangue of one is quartz, the other

sea

Underlying Granite.

Gramte PLATE LXXXIV.

Silver Lead Gash Veins in Faults in Paleozoic and Porphyrite Rocks, Buckskin Canyon, South

These Veins do not extend down to th

Park.

calcite. They occur in the limestone in connection with an intrusive bed of white porphyry. These deposits stand in a vertical position, the beds containing them having been turned up abrupt] against the great London fault, by whose movement the Archean granite rocks forming the easte rn

half of London Mt. are brought up into juxtaposition with the Silurian and Carboniferous beds at its western point.

Going south along the Mosquito range the intrusive porphyries diminish tn extent and with them also the mineral deposits,

The Sacramento mine is a good example of a "pocket" mine. Rich bodies of galena and rich decomposed ores have been found at uncertain intervals ina series of pockets or cavities. Some of these pockets or cavities are empty, and lined with modern stalact.tes, others contain loose

london Hill PO

a53%" ae bs PS efasets . tetas — 7 oo whe ' . é &%e ee

——, Ggranité C+ mefenceae vphyry a —— ee ' Granite London Hill A " sy

' % - Granite eee

a —

a PLATE LXXXV. The London Mine Fault.

sand, with pebbles of rich ore, others are quite full of rich ore deposits. These deposits are difficult to follow with any degree of certainty, and much of the profits made in the rich pockets has been used up in blindly "gophering" after other pockets. From some of these chambers open fissures or joint planes ascend to the surface. The limestone was originally capped by a porphyry which has since been eroded off. This porphyry doubtless supplied the ore.

Leadville District,

The western Boney of this district is the Sawatc': ranyre of Archean granite. The slope of the Mosquito rang 'n th:

east and the hills on the north, forming the water shed between the Grand and Arkansas Rivers, have a basis of Archean granite and gneiss more or less covered by patches and remnants of the Paleozoic formations, ¢. e., Cambrian, Silurian and Carboniferous, which have escaped erosion.

Their lower position relative to corresponding beds on the eastern or South Park side of the sae ai range is due in part to faulting, and in part to folding of the beds.

Within these Paleozoic fremattons, these beds of quartzite and limestone, there zs an enormous development of eruptive rocks, principally quartz-porphyries partially occurring as dykes but generally as immense intrusive sheets following the bedding plane of the sedimentary rocks.

Glaciers have been at work also in this neighborhood. A huge "mer de glace" occupied the great valley of the Arkansas to whose bulk numerous side glaciers contributed; these glaciers have carved and sculptured the mountains. In the flood period following the first glacial epoch a lake was formed occupying the head of the Arkansas Valley. The stratified gravel and sand beds which were deposited at the bottom of this lake now form terraces bordering the valley of the Arkansas River. These beds, known as "wash" or placer grounds, yield gold and are open to further development. Leadville is the center of the mining district, the ores are argentiferous galenaand zinc-blende, They are smelting ores. Their value is increased by their having been oxidized, the lead occurring as carbonate, the silver as chloride in a clayey, or else silicious, mass of hydrated oxides of iron and manganese.

The ore is Bc ay confined to the horizon of the "blue" or Lower Carboniferous limestone, covered by an intrusive sheet of "white Leadville quartz-porphyry." The ore bodies occur not only at the immediate contact of these rocks, but extend down in irregular pockets and chambers into the mass of the limestone, sometimes toa depth of 100 feet. Sometimes the ore completely replaces the limestone between two sheets of porphyry, as in the "Col. Sellers mine," Chrysolite, Little Pittsburg, and on Fryer Hill. A few ore bodies occur, carrying more gold than silver, found at other horizons,. usually as "gash" veins running across the stratification or along bedding planes. Such are the Colorado Prince in quartzite, the Tiger and Ontario in the Weber grits of the Middle Carboniferous.

The "Printer Boy," one of the oldest mines, has_produced a good deal of gold, found as free gold associated with

carbonate of lead and galena, passing down, as is usual in gold mines, into unaltered auriferous iron and copper pyrites, which occur ina body of quartz-porphyry along a vertical cross-joint or fault plane in the porphyry. The gangue is a white clay resulting from decomposition of the quartzporphyry and though the clay ore is rich, it shows no minerals to the eye.

The Paleozoic formations, together with the intrusive porphyry sheets sandwiched in between them, have been compressed into gentle folds, and where the fold was at its greatest tension, a series of parallel faults have occurred having a general north and south direction; their uplifted side is generally to the east.

The prevailing eruptive rock is the "white Leadville porphyry," occurring generally above the blue limestone but also in places below it and at other horizons.

There are also other intrusive sheets of different varieties of quartz-porphyry. The ground is generally buried beneath a hundred feet of glacial moraine material, locally called "wash."

The general geology of the South Park and Leadville region has been so elaborately traced by the labors of the U. S. Geological Survey that we cannot do better than give an abstract of their report in this connection :

Mosquito Range,

A study of this range is necessary to the understanding of the Leadville ore deposits, which occur on its western side. It comprises a length of 19 miles along the crest of the range, and in width including its foothills bordering the Arkansas Valley on the west, and South Park on the east, a slope, in one case of 7% miles, and in the other of about 9 miles. All of it is about 10,000 feet above the sea level.

The range has a sharp single crest trending north and south. To the west this crest presents abrupt cliffs descending precipitously into great glacial amphitheatres at the head of the streams flowing from the range. Mts. Bross, Cameron and Lincoln constitute an independent uplift. The abrupt slope west of the crest is due to a great fault extending along its foot, by which the western continuation of the sedimentary beds, which slope up the eastern spurs and cap the crest, are found at a very much lower elevation on the western spurs. The jagged step-like outline of the western spurs is due toa series of minor parallel faults and folds.

See bing tM Sy SR

go 3s

ton aha

signa

Bas

Perea aot

The secondary uplift of Sheep Mountain on the eastern slope is due to a second great fold and fault.

The elevation of Mount Lincoln is the result of the combination of forces which have uplifted the Mosquito range and those which built up the transverse ridge separating the Middle from the South Park.

The range has been sculptured by glaciers into canyons, and the Arkansas valley is covered with horizontal terraces representing the distribution of material by waters, on the melting of the glaciers.

In the seas of thy Paleozoic and Mesozoic eras which surrounded the Sawatch islands, some 10,000 to 12,000 feet of sandstones, conglomerates, dolomitic limestones and shales were deposited. Towards the close of the Cretaceous, eruptions occurred by which enormous masses of eruptive rock were intruded through the Archzan floor into the overlying sedimentary beds, crossing some ot the beds, and then spreading out in immense intrusive sheets along the planes of division between the different strata.

The intrusive force must have been very great, since comparatively thin sheets of molten rock were forced continuously for distances of many miles between the sedimentary beds.

That the eruptions were intermittent and continued for a long time is shown by the great variety of eruptive rocks found. That this eruptive activity preceded the great movement at the close of the Cretaceous, which uplifted the Mosquito range as well as che other Rocky Mountain ranges, is proved by the folding and faulting of the porphyry eruptions themselves.

In the period intervening between the close of the Cretaceous and the deposition of the Tertiary strata, during which the waters of the ocean gradually receded from the Rocky Mountain region, the pent-up forces of contraction in the earth's crust, which had been long accumulating, found expression in dynamic movements of the rocky strata, pushing together from the east and the west the more recent stratified rocks against the relatively rigid masses of the Archean land, and thus folding and crumpling the beds in the vicinity of the shore lines.

The crystalline and already contorteu beds of the Archawan doubtless received fresh crumples in this movement.

A minor force also acted north and south, producing gentle lateral folds along the foothills at right angles to the trend of the range. These movements were not paroxysmal

or sudden and violent, but protracted for an enormous lapse of time, and appear to be continued in diminished force up to the present day.

SUMUSLULICS ALU SAILS CULO UEEU SreREU ER BNyKvenee Nee ween neighborhood, which are less susceptible to percolating water. The Paleozoic formations in America are the principal repositories for lead and silver ores, not by reason ot their geological age, so much as by their containing such a quantity of soluble limestones and being physically as well

or sudden and violent, but protracted for an enormous lapse of time, and appear to be continued in diminished force up to the present day.

Cretaceous Crelerceotes Crevamceous Jura .as Archaeara SieraMreas Sierra Trias Carborrfervtis Granite CEPOOMRESEPr OLS Carbontfereu Silurian, waa 7 Stl te rrr, Levelt of Mesos ovesSea Selreriars Se SS OO See ain os . : ¥ ee es on einen Np amet a met ad a aa OS a eI! 2, ile EETT (ras 'i MaweateAr Archacanlsland Granctle Floor Vol. detead Section, showing Paleosovc and Mesosote Strata, with intrusions Of eruglies Rock, lynne beneath/

Vountain elevation at close of Creta SuralTrias

g Grrworraprets, Grantce bat Qe ; ] ACesoxove : fo as ) — a Spine, pis ey + ff Ss -— rz (E a A Pox aes —y¥ ek -i"4/ ¥y, y 4 ' a —S: eZ os ¢ s

N Sau ead A "Ue aT (Arkan. 90x85 Volley Atosgutlo Range Voree : Dewressvcor P

ce COOLCT(

No. 2. /deal Section, showing result of the event Post Cretaceous uplift

R & x g My 3 3 a 4 y me ¢ 3 8 i S gp ys 38 5 Silerany a 3 : x 3 M4 ters me") va 5 x Ss 8 2 3 "ras riage A & £ 3 Ovtacecues ! if Ys ; Qualernary g g Q - "OPK 4 f \X& . xs rbd ad eae PE a 7 é ec samme ae sara ee / / /

x eave ate a slang Leadville District Mosgurte Range

Vo. 3. Average Section of Leadville District, Mosy gusto Range and South Park as tt ts

Plate Lxxxvi.

Sections to Iustrate the Gradual Geological Development of the Lea

DAMUSLOMOCS AMG SUMAI~D CUE rote Chew weneue RY ween neighborhood, which are less susceptible to percolating water, The Paleozoic formations in America are the principal repositories for lead and silver ores, not by reason of their geological age, so much as by their conti aining such a quantity of soluble limestones and being physically as well

ous lapse force up

Credwcroat Cretticecd tes

pas ee Tt tas ; / pis "- Trias — a OMT Orotes ar ree a couse Selurinre ' ott rs ere) ' : ; " eal tluricgen — sss SS SSerrercecenest

a ott gee ees es tarts Rsk ath re — aoa a meece oar a ——g —£ aaa -—— Frarncle Ftoor Cotorade Front Range Jstand

es of er wgtive Rock, lying beneath the Mesozoic Sea, between Sawatch and Front Range Islands prior to the great beretacin elevation at close of Cretaceous,

Juralrvas Carborife eT)

PSC i a"re

Foothvte

"N Plairis

hicear : ¥ : ——— - a A h ES Te Range South Park Basin Cotoracdofront Range Upirft

fthe great Post Cretaceous uplift and the folding up of the Mosquito Range.

N

r § x Lt ak Sit iN 3 & Cretaceous bo Sp Seep ME. x hate ArchacanGranste Gnesss ¥ ; ae ga

—— Gretareneees Silursan ) e sh

bd 3 A Se SS 4 36 Notauite Range : South Perk Basin Colorado FrontRange

10 Rance and South Park as tt ts to-day, showing result of faulting and subsequent erosion, PLATE LXXXVI,

ecological Development of the Leadville and South Park Region, Colorado.

wee

perc ol; iting

the prin- - reason ol! ning such a ally as well

The secondary uplift of Sheep Mountain on the eastern

slope is due to a second great fold and 'ault. The elevation of Mount Lincoln is che result of the com-

in the vicinity of the shore lines.

The crystalline and already contorted beds of the Archaan doubtless received fresh crumples in this movement.

A minor force also acted north and south, producing gentle lateral folds along the foothills at right angles to the trend of the range. These movements were not paroxysmal

or sudden and violent, but protracted for an enormous lapse of time, and appear to be continued in diminished force up to the present day.

Mineral Deposition,

It was during the period intervening between the intrusion of the eruptive rocks and the dynamic movements which uplifted the Mosquito range, that the original cepositions of metallic minerals occurred in the Leadville region in the form of metallic sulphides, though now they are found largely oxidized and in other combinations. They were derived from the eruptive rocks themselves and are therefore of later formation than they. Their having been folded and faulted with them shows that they must have been formed before the great Cretaceous uplift, and therefore they are Ider than the Mosquito ras. itself. The deposits were formed by the action of percolating waters taking up certain ore materials in their passage :hrough neighboring rocks, and depositing them in more concentrated form in their present position. This may have taken place while the sedimentary beds were still covered by the waters ot the ocean, and the waters therefore may have been derived from it, or the area of the Mosquito range may have already emerged from the ocean and the waters have been estuarine. The uplift of the Mosquito range consisted of a series of folds fractured by faults. The crest is formed by the Mosquito fault, another parallel fracture is the London fault. The greatest movement is towards the center or Leadville region, dying out at either end north and south ; the greatest displacement is 10,000 feet. Whatever cliffs may have originally been formed by this faulting have been planed down by glacial erosion,

Origin Of Leadville Ore Deposits,

The ores are deposited for the most part in the blue limestone of the Lower Carboniferous. As the ores were deposited by water solutions, the soluble limestone — beds would be more easily acted upon by solutions than the sandstones and shales composing the other rocks of the neighborhood, which are less susceptible to percolating water. The Paleozoic formations in America are the principal repositories for lead and silver ores, not by reason ot their geological age, so much as by their containing such a quantity of soluble limestones and being physically as well

ff

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as Chemically favorable for the reception of mineral solutions.

The physical structural conditions of Leadville are particularly favorable to the concentration of percolating waters in the blue limestone, Great intrusive sheets of porphyry follow the limestone persistently, principally on its upper surface, This porphyry is very porous, and full of cracks and joints, affording ready channels for water from above, and also channels for ascending water from below, along the walls of the fissures, through which it is erupted, Such waters passing through a medium of different composition would be ready for a chemical interchange with the limestone,

Composition Of Ores,

The ores were deposited originally as sulphides, This is shown by the fact that the oxidized ores near the surface pass down with depth into sulphides. In Ten-Mile district these oxidized ores are seen to result from the alteration of a mixture of galena, pyrite, and zinc-blende. There is very little gold in the average Leadville ores; what little there is comes from the Florence mine (native gold), and from others where it is associated with pyrites. It is usually associated with porphyry rocks, and a porphyry commonly

called pyritiferous porphyry shows gold to exist diffused through the pyrites disseminated through its mass.

Stlver occurs as chloride, a secondary condition, its original condition probably being sulphide.

Lead occurs as carbonate and sulphate and, deep in the mines, as sulphide, Specimens are common of galena nodules surrounded by a thin coat of sulphate, and that again by a coat of carbonate, showing the order of transition from sulphide to sulphate and thence to carbonate.

In the iron mine native sulphur occurs as an alteration product of galena,

/ronald manganese constitute rather a gangue material than adore. Theyare hydrated oxides and protoxides, The iron was originally deposited as sulphide or pyrites, but has been wholly transformed by oxidation.

Zinc is not common, but occurs as calamine (zinc silicate) in needle-like hairs and white crystals in cavities in the mines. Its original form was zinc-blende (zinc sulphide), as shown in the Ten-Mile district.

The earthy minerals, alumina, lime, silica and magnesia, are in fair proportions, as might be expected from ores which are a replacement of limestone in close connection

with porphyry. The alkaline element among the ores might also be traced to the influence of the latter rock,

The agents of alteration were surface waters, which contain everywhere carbonic acid, oxygen, organic matter, chloride of sodium (common salt), and phosphoric acid, The rocks through which these waters passed, such as porphyries and limestones, were found to contain phosphoric

'id and chlorine, while organic matter exists in the blue

mestones ; and in the overlying shales and sandstones are many carbonaceous beds and even beds of coal. Water passing through these rocks would take up all these elements and be ready for chemical reactions.

Galena (lead sulphide) is much richer in silver than its alteration product, carbonate of lead, or cerussite. On Carbonate Hill the carbonate averages 40 oz. silver, the galena is 145 oz. to the ton. But galena is harder of treatment.

Silver is found at times disseminated through vein matter and country rock, without the presence of lead, proving that during alteration silver was removed farther from its original condition and more widely disseminated than lead,

Outcrop deposits have provedin n ny cases richer than those at depth. The deposits near the surface have been the refined, concentrated remains of larger bodies gradually removed by erosion, as the alteration by surface waters went on, The baser and more soluble metals have thus been removed in solutions, leaving behind the more valuable and perhaps less soluble metals in new and richer secondary combinations.

Kaolin" or "Chinese talc," which occurs both along the line of contact and between the porphyry and limestone and also in the heart of the ore deposit, is a decomposition product from porphyry. It consists principally of hydrated silicate of alumina derived from the feldspars of the porphyries, perhaps at the time when acted upon by sulphurous. waters, Which brought in the original ore deposits.

Calette occurs incrusting recent crevices and lining recent cavities.

Barite is common, generally associated with chloride ot silver and manganese and is locally recognized as a sign of rich ore.

Mode Of Formation Of Leadville Ore Deposits.

The ores were deposited from water solutions by a metasomatic interchange, 7 e, Substance exchanged for substance with the lime tone ; and lastly e+ originally as sulphides.

—

Mineral matter is carried from. ae place to another within the earth's crust by heat and water, or these combined, Metasomatic interchange of metal for limestone and the removal of dolomite could only have been produced by water. The ores were nof deposited in pre-resténg cavities, but are a replacement of the country rock, 2 é, dolomitic limestone,

The ores grade off gradually into the material of the limestone, with a definite limit, as would not have been the case if the limestone had been previously caverned, The only limiting outline to the ore bodies is that formed by the contact porphy ry.

Fragments of unaltered) limestone are found entirely enclosed within the ore bodies, and ore bodies often occupy the entire space for long distances between two horizontal sheets of porphyry, w hich space further on is occupied by the limestone. This is well seen in Colonel Sellers mine. Examination of ores and veinstone shows lime and magnesia not in the crystalline condition they would have, had they been brought into a pre-existing cavity and de posite 'dd, but in the same granular condition in which they exist in the country rock.

The deposits in rocks other than limestone consist of metallic minerals and of altered portions of the country rock, in which the structure of the latter can sometimes be still traced, and are not the regular lavers of matter foreign to the country rock, which results from the filling of a pre-existing fissure or cavity by materials brought: in from a distance and de posite d along the walls.

In the Ten-Mile district the arrangement of the particles of the original rock is Trequently seen to be preserved in the metallic minerals, which maintain a certain parallelism with the original bedding planes in the lines defined by minute changes in these minerals.

The common characteristic of caves which have been dissolved out of limestone is, that their walls are coated with alaver of clay which has been left undissolved by the percolating waters, and these walls have a peculiar surtace of little cup-shaped irregularities from which also. stalactites frequently hang, There is also an accumulation at the bottom of the cave of fragments of limestone, fallen from the sides of the roof. None of these characteristics are found associated with the ore replacements.

Also, when mineral matter is deposited in " pre-existing cavities' it takes the form of regular layers parallel with

the walls of the cavity, as is beautifully shown in geodes lined with a succession of zeolites or with layers of chalcedony, opal and quartz,

No such successive arrangement in layers is found in the Leadville ore bodies,

Again, could suc h large, open cavities have existed for long distances without support between the layers of porphyry ?) Why did not these porphyry sheets close together ? And further, how could such extensive cavities have been formed and kept open under a pressure of 10,000 feet of rock, Which the geology of the region shows to have existed above the deposits at the time they were being formed ? Such cavities as we do find in the region are all of very recent origin, Cutting through both limestone and ore bodies, and have been hollowed out by surface waters more recent even than those which produced the secondary alterations in the ore bodies,

The ore deposits of Ten-Mile district about Kokomo, not far north from Leadville, are very similar in character to those at Leadville. They occur, however, in a somewhat higher division of the Carboniferous, and the ores as a rule are not so decomposed and oxidized, and the transition from the original sulphide character of the deposits to the oxidized condition is more easily shown,

Red Cliff Gold Deposits,

At Red Cliff, still further north of Leadville, in the Valley of the Eagle, the same geologic series are found, penetrated, as at Leadville and Kokomo, by eruptive sheets. In the limestones at contact with the porphyries, much the sume classes of ore deposits occur, but the pec uliar and instructive feature of the camp is the rich deposits of gold in chambers and cavities in the hard and usually unproductive Cambrian quartzites resting on the granite.

The gold in these chambers often occurs as nuggets. The quartzites dip about 10° N. E., and between their bedding planes lies the ore. The so-called contact or bedding plane between one stratum of quartzite and another is clearly defined. At this line there is a filling so to speak of breeciated," broken up quartzite fragments cemented by iron rust and at times by iron pyrites. The thickness ot this breccia varies between four and six feet. Ore chimneys on this breecia occur at intervals.

Their presence is indicated on the outerop by seams of rusty clay, which lies on top of the ore body and follows it along the roof of the de pusit for 100 to 200 feet, then thins out gradually and disappears entirely; at the point of "s disappearance, unaltered iron vyrites set in,

These ore chimneys are about 4 feet in width, their thickness is limited to the space between the floor and roof, The quartzite roof is always smooth, but the lower quartzite floor is rough and corrugated and shows chemical action on it attendant on deposition of ore, The floor at times is impregnated with ore which does not, however, extend any great distance into it. Though the ore chimneys are from 4 to 6 feet wide the pay ore is only a few ine hes, swelling from floor to roof. The pay ore in the oxidized rusty portion yields 7 ounces gold and 50 ounces silver.

In mining, the floor is followed as a guide, Individual ore chimneys are connected laterally by ore chutes like a network, These ore chimneys div ine and separate, the branches reuniting or again splitting u The whole ramification comes together again at intervals in one main chimney. The rock filling the space where the divergence has taken place is the same as the breccia filling, only more compact and impregnated with pyrite. These fillings are left standing as pillars after the ore is mined,

To sum up, the characteristics of these deposits are :

First, Vhe outcrop of the ore chimney indicated by what is locally called a " joint-clay.'

Second, A zone of oxidation for 200 feet, which gradually merges, as the natural water level is approach hed, through a zone of mixed oxides and sulphides to the zone of unaffected sulphides.

Third, The "joint-clay" gradually disappears as the sulphides are approached, The ore on analysis shows sesquioxide and sesquisulphate of iron, silica and alumina and sulphate of barium.

In the Ground Hog mine the ore chimneys are 600 feet apart but are probably connected. They abound in nuggets; the latter are sometimes twisted like bent horns ; in other chutes they are lumpy, composed of crystalline gold e articles cemented together by sesquisulphate of iron and

1orn silver.

Nuggets are found in troughs in the quartzite floor imbedded in clay associated with rich silver or horn silver ore, With the nuggets are lumps of sesquisulphate of iron carrying much gold, .This proves, according to Mr, Guiter-

man, that the secondary deposition of gold in crystals was through the medium of persulphate of iron derived from slow oxidation of iron pyrites, and is an admirable contirmation of the theory as stated by Prof. Le Conte in his Geology. ,

Aspen Ore Depostts,

The Aspen mining region is geologically related to that of Leadville; each is on the shore line of the old Aechaan island of the Sawatch, one on the east, the other on che West, opposite one another, but about 50 miles apart,

The ore deposits occur in the same general horizon, viz. the Lower Carboniferous.

Both regions show intense disturbance, both by voleani: intrusions of igneous rock, folding, and faulting. The process of ore deposition in both regions has been an ac tu il replacement of the country rock by vein material.

At Aspen the ore is not found in ae/va/ contact with the overlying eruptive igneous rock, but at some depth down in the limestone, at a zone where the "blue limestone" becomes dolomized, or as Aspen miners say "passes from blue lime into short lime.'

The mines of Aspen are situated in Paleozoic strata reclining upon the slope of a narrow ridged mountain, forming a granite spur "ev eche/on" with the Sawatch ri inge.

The strip of country in the vicinity of Aspen constitutes the dividing line between the two distinct uplifts of the Sawatch range on the east, and the Elk mountains on the west, and has been successively atlected by each upheaval,

The Sawatch upheaval was a gradual elevation of this mountain mass resulting from a gradual subsidence of the adjoining sea bottoms, which caused the sedinientary beds deposited in those sea bottoms to slope up at varying angles all along the ancient shore line toward the central mass of the Archwan island.

Vhe Elk Mountain range, which extends to the west and south of this region, was upheaved later than the Sawatch, with greater violence and eruptive energy, and the upheaval was accompanied by enormous intrusions of eruptive rock which were forced into the sedimentary strata already shattered by the forces of upheaval, in great " laccolites," or solid masses, and spread out through them in every direction in the form of dykes and intrusive sheets, The surface exposures of these igneous bodies cover areas ot twenty-five to thirty square miles, and their extension below the surface is doubtless very much greater,

" "4

The intrusion of such enormous masses Of foreign matter must not only have greatly disturbed the beds within the region otf up heaval, but also have so expanded the volume of the earth's crust im this area as to cause a severe lateral pressure in the adjommng region, Phat adjoining region was Aspen and its neighborhood

Ht would be justin the strip ot sedimentary beds along the Aspen Mountain ridge, whieh is backed by a projecting: pommt of the un wielding Sawateb Arehiean, that this compression would be most severely felt, the Sawateh granite mass wehing as a pomt of resistanee against the mitense laterabeompres ston caused by the younger Elk VMountarn uplift,

Phe sedimentary beds resting against the Archiean correspond generally, with sheet differences, to those in the South Park and Leadville region tna similar post tion

Phe latter were deposited ima partially enclosed bay, now const tuting the South Park basin, the former oon the west side ot the Archiean tshind ina wider and deeper sea, and oon this) western slope the beds are generally much thicker than those of correspond ing geological horizons on the east,

Sp Ratigorapey Of Aspen,

1, The horizons re presented ane the Upper Cacnbrian quartzite 100 feet, resting on the Arechoean errand

Silurian stlietous limestone and quartzites, 340 feet

Darker limestones, rusty

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brown and dolomitic at base, blue compact and pure on top, 240 feet. (These are Lower Carboniferous.)

4. Carboniferous clays and shales and thin bedded lime stones, 425 feet. These belong to the Weber grits (Middle Carboniferous).

5. A series of variegated green and red sandstones, clays and shales, some limestones and red sandstones of the Upper Carboniferous,

6. Heavy bedded red sandstones (Triassic).

Above these again are several thousand feet of Cretaceous strata, up to the base of the Laramie coal beds, (The Cretaceous, however, and the Jurassic do not rest immediately upon the granite),

Diortte—On Aspen Mountain is a bed of "white porphyrv" (diorite) in the black shales, 60 to too feet above the top of the blue limestone. It is 260 feet thick on the slope back of town, but thickens considerably to the south, and is traceable to Ashcroft. It appears to extend also across the valley of Roaring Fork to Smuggler Mountain. Small intrusive sheets also occur in the lower quartzites near the point of Aspen Mountain and on the east face of Richmond Hill.

As affected by the Sawatch upheaval, these beds wrap around the Archwan mass, resting against or dipping away from it at varying angles,

The quartzites and limestones cross the valley of Roaring Fork from Smuggler Mountain to Aspen Mountain, striking northeast and southwest, dipping northwest. The angle of dip is about 45°, varying from a minimum of 30° toa maximum of 60° in " flats' and "steeps."

The Ore Bodies.

The lower carboniferous " blue limestone" is compact, homogeneous and composed of pure carbonate of lime. The "brown" or "short"? dolomitic limestone is of a dark gray color, finely crystalline, finely granulated and traversed in every direction by a network of minute veinlets containing iron salts, which, when oxidized, color the surface a rusty brown. The oxidation along these minute veins makes the rock break easily into dice-shaped fragments giving the rock a' crackly " structure, hence its local name of short lime.

Ore Distribution.— The outlines of the ore bodies cannot be detected by the eye, owing to the gradual transition from ore to country rock,

The ore is not confined to the brown dolomite below the

Q

so-called contact, but several ore bodies extend 20 or 2 feet above this contact into the blue limestone and in some cases follow the lines of cross-fracture entirely across the blue limestone,

The ore is not confined, either, to a d"finite plane or COontact between two dissimilar beds of limestone and dolomite from which its solutions have eaten into the underlying dolomite, for in the first place there is not one single contact, but many; and if this so-called contact constitutes an essential condition of ore deposition, there is no reason w hy it should be confined to the one and not found in the others where the rocks have the same composition, Again, orebearing solutions would not be likely to eat upwi rds for any great dist: ince trom the contact plane if they entered the beds along this plane.

This so-called contact plane is well defined on Spar Ridge and continues down with the dip in the underground working, but ore bodies occur above and below it.

The rock thus mineralized is dolomite in most cases, but it is none the less above the true bedding plane called the contact,

In other parts there has been fracturing across the beds as shown by a vertical breccia of limestone fragments with a cement of iron oxide and manganese,

Over the ore bodies are lines of open cavities tollowing the lines of cross-fracture, through which the ore solutions passed which deposited the ore bodies, These caves are now being hollowed out by water descending from the surface dissolving the limestone in the roof and flowing off along the floor, depositing a mud of silica, alumina, lime, magnesia and iron oxide,

Hlence this contact is not necessarily the only ore channel of the district, and other channels may be sought tor

Portions of the Gre bodies have been formed by solutions percolating through cross-fractures and spreading out between the parallel bedding planes.

This would happen if these solutions derived their metals from the overlying porphyry, for it is separated trom the limestone by argill: iceous Shales which would be impervious unless fracture id across the bedding. The analysis of the lime mud at bottom of the cave shows by its pre ponde rance of alkalies, which do not exist in the composition of either brown or blue limestone ,that the waters dissolving it cam: from the porphyry. The waters brought both alkalies and sil ca from the porphyry, and probably the iron and baryta

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Dolomppization,

This is a secondary process upon the blue limestone by magnesian waters, which is proved by irregular tongues ot dolomite extending up, into and across the blue limestone, The lenticular bodies in the Durant cliff point to the same fact. The crackly structure of the brown lime results from the replacement of a molecule of lime by a molecule of magnesia, involving also a contraction in' volume of the rock itself, which would cause it to separate in angular fragments, the intersections filled by material more soluble than the rock itself,

The magnesian waters may have been connected with those which brought in the vein materials,

In the ore bodies the partially mineralized rock on the borders of the ore is changed to dolomite, hence dolomitization either preceded or accompanied ore deposition,

Mr. Emmons suggests as probabilétéces only, that the poryhvry intrusion preceded the faulting ;

That the ore deposit followed the intrusion of porphyry and tso the principal faulting movements ;

Tiiat small movements have taken place in recent times both in the strata and contained ore bodies since the oxidation of the latter; that at the time of the great faulting, the beds may net have attained entirely their present position

In the vicinity of Aspen Mountain ore bodies, the strata appear to have been synelinally folded and faulted between the main Archwan area on the cast, and a mass of granite at the western extremity of the mountain, thus producing a second series of Oppositely inclined beds, also containing a lew ore bodies, Intrusions of altered eruptive diorite occupy i prominent position in the intervening trough and may have seriously faulted or dislocated the strata in the depths. he bulk of the Aspen ores are largely oxidation products otargentiferous minerals with true silver minerals, associated with calespar and baryta; itis a "dry ore" requiring to be mixed with silicious lead ores before it can be treated. Such rich ores as polybasite and brittle silver occur also,

A great deal of the ore consists of tine grained steel galena, very rich in silver,

Aspen As A Prospecting Ground,

Aspen again is an exampleof a region that had often been AvMed over by the prospector and abandoned before the final thorough prospecting revealed its great riches, Years

ago some prospectors found signs of float and © blossom" cropping out under the blue limestone of Spar Ridge. They even went so faras to sink aa incline of a hundred feet o1 more, but though they found ore, its character was so low grade, that the mine was for a long time shut down and practically abandoned, Then an enterprising individual conceived the idea of boring down on the sloping back of the limestone in the adjoining Vallejo gulch, to tap the ore body, already discovered along the outcropping, on the underside of the limestone, At about 150 leet deep the limestone was pierced, and an enormously large and rich ore body was discovered, Immediately, the original locators began again with all speed to push on their incline, and then originated the celebrated apex and side line" lawsuit The original locators had the apex on the outerop., 'They

therefore claimed the whole mountain, aoc tried to drive out the side line me Finally a Compromise was etteected, but that boring dewn on the back of the mestone and its discoveries led immediately to an army ot prospectors ex amining the mountain, and it was astonishing how n Vor deposits were discovered in a region that was supposed to have beeu prospecied and given up as no good, Of cours Aspen is an exaupls of "azchness with depth." XN den OUS precede. t and encouragement to that often rumors pics of runnése long cross-cut tunnels to cut an ore body at depth, whici has only proved indifferently good near the urface, the fallacy we have before alluded to, of the

improbable probability of "richness increasing with depth

An Exampli -F Prospecting,

Now supposing our prospector was the first man to cater that region years ago, Whit signs were there to lead bin, to think it was a good prospecting ground? supposing hima te be fairly versed in geology, he would have hot fi, ald he came down over the Sawatch range, that the Paleozoic

trata he had observed as ore-bearing at Leadville, out- ' dropped also on this western side, together with the " blue limestone; " secondly, he would have noticed the presence of large masses of evuféérve rock constituting the Elk range ; thirdly, he would observe the region was much disturbe

that the strata were intensely folded, and intensely faulted, All these signs he would have considered likely, Then after following up the various creeks, he would select such

spots as where he saw the massive blue limestone out-

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cropping. Ile would readily find this bed from its relation to the granite and Cambrian quartzite below. He would look for places where porphyry was intruded into the limestone or where gre at masses of it lay above or in vicinity of the limestone. This would probably have led him, on nearing Aspen Mountain to give that mountain more than a peeing look. He would notice that the strata on Aspen

Mountain were very much disturbed and faulted, that a spur of granite, quite out of place, came right up through the middle of the mount in, that strata were pitching in various directions off from this, and moreover that in the lap of this fault-fold was a very thick bed of porphyry. Tle would observe the line of change from the blue limestone to the dolomite, and at that line he would have prospected and found and followed up the " blossom" at the line, consisting of calcite and baryta running in a rusty line, like the outcrop of a coal seam, all up the side of Spar Gulch and so he would have discovered the great Aspen ore-deposits, and by following up the indications along the outcrop and locating claim after claim as along an outcropping coal seam, he couid b .ve secured practically the whole "apex" of the hill, and become master of the mountain and all it contained ; but had he known then the litigation of "side line and apex" that was to arise, he should have gone further, and located claims covering the side line, on the back of the sloping limestone ridge, leading down into Vallejo gulch. But again he might, like the original first discoverers, have become disheartened with his find on testing the outcropping ore by assay or mill run, and finding it so low grade neat the surface. On general principles in this respect he would have been right.

Now having thoroughly explored the little Aspen Mountain, he would observe that much the same formations crossed the creek and entered into Smuggler Mountain, though much obscured by heavy glacial drift. Here he might have located fresh claims on this hill,and become the owner of the celebrated Smuggler, Regent and other mines with their untold wealth. Thence he might have continued his successful trip, and followed the same so-called " contact' outcrop for miles on to Asheroft. It must be remembered here, however, that in locating all these claims, whilst the prospector may drive his location stake at every 1,500 feet, he is required within sixty days after location, to dig a ten foot hole in each location, As this may be a little difhcult for him to do he generally enlists others in his enter-

prise, to assist him, and enters some of the claims in their names, to prevent the discoveries being jumped by a horde of prospectors who press in as soon as anything is found Good advice to a prospector, is to keep very still and "mum about his discoveries until he has well secured them, and to be very careful how he " opens his head" to any one. Commonly a prospector who has "struck it," comes into town fills up with whiskey, "blows it in," and then, blows it off' all over town about his discovery, andis elated to tind himself the hero of the hour, The result is, before daylight the following morning, a hundred men are chasing ove another in the direction of his discovery, and before a day or mor is over, the mountain is covered with locations as close as graves in oa citv churchyard, and in a week's time thes locations are covered again by a second layer, as the saving is, 'several feet deep." , A boom follows. The offscourings of the country pour it with the saloon, dance hall and gambling hell element. murder or two follows, Lynch law takes a hand. Then a here of real estate men come in, and lots are sold at fabulous prices, and the town is inflated with a population and everything else usually far above the capacity of thi mines to support. A collapse follows, and a steady retreat of hollow-eved, disappointed adventurers, Intime the town and camp assume their lawful) proportions and business settles down to its lawful regime.

Whilst all this has been going on, and amidst all the tuss and bustle and " hooraying" of real estate "boomers " and so forth, some prospectors have been quietly trying to follow up the first desirable indications into the neighboring region, resulting often in an extension of the ore-bearing region. Some of these locations are 'bona fide" and valuable. Other "holes in the ground" are dug on the merest pretext of indications to catch the ignorant, adventurous tendertoot capitalist purchasers, or 'suckers,' An investor going into the camp at such a time, tinds a

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Pa) fabulous price placed on every prospect, Whether genuine o1 false. Asa prudent man, he either beats down such prices

or concludes he will visit the camp a little later, when the excitement and inflation has gone down, and when thing are on more of a business footing, and something like the real value of the camp has been found and proved, Ot course in such a gambling speculation, by such prudence and delay he may lose a lucky chance, but he has preserved his prudence and escaped being wofully bitten.

Perhaps in a month's time, the discoveries are found to be merely superticial, the boom utterly collapses, and the dreary sight is seen a little later, of a desolate village, with frame houses and log cabins, and possibly a mill or two, for mills are sure to follow, lying in wreck and ruin, a home for the owls and the bats; or else the genuine discovery produces one or two mines and supports a handful of population legitimately,

Again, a region like Aspen may disclose a limited number of very rich ore deposits, but) suflicient to support and sustain a fair sized town,

But the most important and most lasting discoveries of allure of areas producing an immense quantity of low grade ore such as Leadville. This gives an opportunity for a great number of mines and for the support of a large and permanent town

CHAPTER Alltrl.

Examining And Sampling Mining Properties, Prospects Or Mines.

A prospector may be, or become, a " mining expert" and be called upon to make examinations of mining properties, whether prospects or developed mines, so a few suggestions may prove useful,

Mining properties of the precious metals are generally ot two kinds, those containing ore deposits in place, such as fissure veins and blanket deposits and placers, the latter being gold-bearing, In both cases, and especially in' the former, the character, position and other relations of properties are infinitely varied, so that no hard and fast rule can be given to suit all cases; certain rules, however, will generally apply.

A mining engineer receives a letter from a company tell ing him to go to such and such a country or region and examine and report on a certain property that has been offered them, Such a mandate is usually accompanied by a letter or report from the owner or parties offering the property, giving the owner's description of the same, or else the report of some expert on it. As a general rule such reports give the most favorable view, and in some cases must

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betaken "can grano sais." To the mining engineer they give some sort of an idea as to what the property may be like. As to its value, ete., that he proposes to find out for himself, The company sometimes asks him to examine with a View to verifying or modifying or contradicting such reports,

The region, the country, the character of the de posits, the local conditions, m: i inall probability be comparatively new or strange to him, Prior to starting he may make inquiries in mining circles if anything is known about the region o1 district, If there are any published mining or geological reports or maps, he will consult these, Finally he starts out With as little baggage as possible, usually a small hand bag, containing a few necessaries; a tapeline, geological pick clinometer and compass and note or sketch book, [lis dress is generally a suit of corduroys, leather gaiters and strong boots.

As he enters the region by ratlor on horseback he notices the main geological features, whetherthe rocks are granitic sedimentary, or eruptive, Finally he reaches the camp calls on the owner or superintendent and rides up with him to visit the mine. Tf he should "lay over" for the atterhoon in the village, he may as indirectly as possible try to pick up any gossip there may be afloat relating to the prope rtv. tle is at once impressed with the accessibility or inaccessibility of the property, and estimates the probable cost of bringing down the ore to the mill or to the railway track, and observes the proximity or absence of timber and water power At last he reaches the mine, dines at the boarding house, and is then taken over the premises by the superintendent, Tlis first attention is directed to the surlace character of the property, its LOpGaTND whether rolling, smooth or precipitous, whether it is high above the

valley or near down to it, whether the mine is high or low as regards the water level or drainage system of the neighborhood, whether the property is conveniently situated tor working the mine and transporting the ore, ete,

Accessibility is an important matter, [In some regions, such as in the San Juan district (Colorado) for example, mines and prospect holes are sometimes on the top or sides of mountains or precipices, thousands of feet above the valley below, located at spots one would think only an cagle could reach; prospect tunnels, too, are driven where there appears scarce ly a foothold for squid rel, No spot, howe, er, seems too inaccessible for the prospector, Ata glance thi

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engineer sees that in a property situated in such a region, accessibility is one of the first and often most formidable problems to be considered,

To some of these mines are long zigzag trails cut in the side of the mountain, The engineer calculates how much the owners of the donkey or "burro train will charge to bring that ore down to the valley or mill, Hle argues that amine at that almost inaccessible height, ought to carry a good deal of pretty high grade ore to pay even for transportation by the © burros," let alone the cost of freight atterwards to distant smelting works, On the other handa mine whose workings open out within easy access of the valley or railway track, could athord to carry less valuable ore, Then there is timber and water power to be considered, the former tor timbering the workings of the mine, the latter for running stamp mill, or for supplying steam power to the engines of the mine, If there be no water power, and the vein carries free gold, the ore must be carried down to the nearest stamp mill, [na young or virgin" property or prospect, the engineer will look out fora convenient site for such a mill, under a developed property ; if there be a mill on the premises, he will examine and report on its capacity and suitability for treating the ores, Ao mill site must, of course, be selected close to some water power, In some districts there is a superabundance of water, in others ws serious lack of it, or the supply is meagre at certain: seasons, or is frozen up in winter. Some mines are quite dry, but generally they will supply enough mine-water trom thei Workings to afford steam power,

Ife observes the character and dip and direction of the veins if exposed on the surface, examines any prospect holes on them, and takes a few samples for assay, Ele will consider the nature of the ore deposits, whether they are in fissure veins in crystalline rocks, or blanket deposits in sedimentary rocks, or contacts at junction with eruptive porphyries. A great variety of local and minor details have to be noticed which can hardly be specified.

Having looked over the surface, he enters the tunnel o1 workings with the superintendent, As he passes along, the latter is likely to call his attention to this or that spot, as especially good, and naturally he rather overlooks the poorer parts of the mine, Tle may suggest the advisability of taking samples from such favorable spots. The engineer, however, takes little heed, as, if he were to continue his attention to, and sample only these choice portions, he would

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Having traversed the workings and obtained a general idea of the position of the vein and ore bodies, and taking an inventory of the amount of development, length of drifts, shafts, etc. (the latter he can obtain from a map of the mine in the superintendent's office. a copy of which he will send to his company) he asks the superintendent to leave him and his assistant and vacate the mine, as he does not wish any one except his assistant to be w.th him whilst he is taking samples for assay.

Sampling,

Now begins his hard and most telling work, the time and labor depending very much upon the size and amount of development in the mine, or the degree of accuracy necessary. Taking a large strip of muslin, he cuts part of it up into small pieces about the size of a pocket handkerchief, these are to contain his samples for assay, when quartered. Then he takes the remainder of the muslin, or better still an ordinary candlebox, this to catch the mass of small fragments he detaches from the vein with his pick.

Now witha light pick or with achisel and hammer he begins, either from the entrance or end of the tunnel, to detach small portions of the rock, cutting a rough groove across the vein. Sometimes the tunnel occupies the whole width of the vein in which case he will have to make a circular groove clear around the tunnel, across floor, roof and walls as shown in Plate XCIV; the fragments from his work drop into the candlebox or onto the muslin.

According to the length of the workings or the need for great accuracy, he repeats this operation at intervals which may be every 5 feet, 10 feet or 20 feet ; at intervals of say 20 feet, he masses and mixes together all the samples, breaks them up as fine as he can on a shovel and divides the result into four parts, throws away three parts and retains one. This he reduces to a fine powder and wraps up in the small muslin pieces, ties it up and seals with seniwe wax, marking on it the number and other notes, such as to feet from entrance, etc., with an indelible pencil. This work he continues till he has reached the end of the tunnel, which if it be 100 feet long will give him from 20 feet intervals, five little sacks of powdered ore for assaying. As check upon this work and for reference in case of any accident to or any tampering with his samples in transit, he will occasionally take a "grab" sample from his broken rock before quartering it. Here and there, too, he may take a chunk of some

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peculiar rock such asa porphyry or some peculiar streak in the gangue, these he will put in his coat pocket and keep on his person.

It is sometimes important in a vein to find out what rock or portion of rock carries the most value. For instance, on one occasion we examined a vein said to carry gold clear across its entire width of some 50 feet. Now this socalled vein proved to be a decomposed dyke of porphyry

PLATE XCI. impregnated with

Natural Appearance of Mine on a Blanket Ore pyrites and free goid,

Deposit. and through the

dyke ran a net-work

of little narrow quartz veins or veinlets. On sampling, whilst we took samples clear across the whole width of the vein, we kept those fragments which came from the quartz veinlets apart from those which came from the porphyry

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Plate Xcii.

Geological Section Showing Workings and Ore Bodies in Contact Bianket Ore Body. Shaded Portions are All Worked Out.

gangue. The result was we found the porphyry, constituting of course the main element, to be barren and the

gold to be concentrated in the quartz veinlets constituting a minimum of the width,

So in a vein there will generally be parts richer than others, " pay streaks" as they are called, which it is important to distinguish, also certain metallic minerals in the vein Carrying greater values than others. Thus the pyrites, if undecomposed, may prove too poor to treat for gold, or ina silver mine, streaks of gray Copper may be very rich, whilst bodies of coarse galena may be very poor. Ina gold inine it is important for the engineer, if he can, to find out to what depth surface decomposition or oxidation has penetrated, because in this brown rusty matter will likely be most of the "free gold;" whilst when the unoxidized pyrites makes its appearance the ore is no longer free ore, but must be treated by some process other than that of a stamp mill,

Plate Xciii.

Plano-Section of a Flat Ore Body.

and with the incoming of pyrite the palmy days of the gold mine may be at an end. Sometimes, however, though the an oxidized brown gossan may play out and succeed to white quartz, the latter, if it be not too hard, white and " hungry," may still continue to carry free gold in it. Again in the veins, with their descent into depths, greater or less richness may occur or different varieties of ore set in, or absolutely barren quartz, so if there be shafts or tunnels driven on the vein a distinction should be noted with descent as to values found at different levels, also as to character and i richness of the ore above and below water line; the latter i corresponds to the average drainage level of the country. This completes his underground examination, Whilst in the mine he may make a rough sketch or two of the vein

showing the general disposition of the ore bodies or any

peculiarities. On emerging and carefully securing his

samples beyond reach of their being tampered with, he

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PLATE XCIV. fatter is often a difficult and un-

Baport-Taking. rata pies certain problem. He may make

some sort of estimate as to the reasonableness or not of

the price asked and give his estimate; he can form, how-

ever, no true estimate of the value of the ore bodies till he

has had time to assay his samples, for these are the crucial test of the value of the property.

Plate Xcv,

Fissure Vein Outcrop on Hillside Showing Surface Workings,

In writing up his report at his leisure, which will most likely be read at a general meeting of the company, he cannot be too clear, simple and explanatory in his account and its details, as it is to be remembered that the company is

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likely largely to be composed of men unacquainted with mining and mining terms; he must therefore not take it for granted that they know what "stopes," "adits" and "gouge," etc, are, but explain as he goes along, accompanying his remarks with rough sketches to make his meaning clear and put the members of the company as much on the ground as possible. We ourselves have found that it is not necessary, generally to make elaborate notes in the field or to write pages of reading matter then, provided we make many sketches and on them put down items such as length of workings, etc., etc. The sketch is generally the notes, and

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Cross Section of Vein Showing Workings. Dotted Portion is Ore Body, Shaded is Ore Worked Out.

when the engineer returns home, his sketches will recall vividly all he has seen 'and from these he will write his report. Upon certain matters, however, such as involve numbers, he should be very accurate in writing notes and not trust to treacherous memory for them.

Description Of Plates.

In Plate LX X XIX we have an actual example of a rather inaccessible property in the San Juan, which with Plate XC shows the kind of sketches to accompany a report. In Plate LXX XIX with its section, it will be observed how very high up the mining holes and prospects are perched, in most cases over 1,000 feet above the valley, and again, before the ore can be brought over to the mill, a ravine of a hundred feet deep occupied by a boiling torrent has to be crossed. Some of the properties might be worked perhaps

by a suspension tramway thrown across the gulch, In another case a trail has had to be cut in long z gags of some miles before the bottom of that could be reached. Another disadvantageous feature in this property is the number of scattered veins, none of them very rich by itself ; this involves a separate plant or workings for each. One ood vein would be better than all these put together. here is fine water power on the property and plenty of timber.

In Plate XC there is one fine rich gold vein easily accessible and easily worked; below it lies a natural basin and abundant water which makes it an admirable location for the stamp mill. This Plate gives an idea of the rough kind of a sketch the expert makes on the ground, which he embellishes and elaborates on his return.

Plates XCI, XCII and XCIII show:

(XCI.) The surface appearance of a "flat" or contact blanket on the side of a hill, such as at Leadville.

(XCII.) Cross-section showing the position of ore bodies, the portions worked out and portions probably left in reserve, also the workings of the mine anche geological section, together with a prominent fault.

(XCIII.) Is a somewhat ideal sketch of the probable relations of a flat ore body if the surface matter were removed, or rather if it were opened like a book,

Plate XCIV shows the expert taking samples in a tunnel driven in the vein; the vein in this instance, being a very large one, occupies the whole width of the tunnel; this is not generally the case, the vein and ore body are more commonly observed about the middle of the roof, z. e., if the vein is small,

Plate XCV shows the outside appearance of a fissure vein with three tunnels down in it, and Plate XC VI shows crosssection and profile showing the tunnel and the ore bodies so far discovered in the quartz gangue and how much has been worked out.

Chapter Xiv, Salting Mines,

In these days when, owing to the depression of silver, so much attention is being turned towards gold and gold mines, too much care cannot be taken by those investing or act ing aS examiners or experts in gold mines, that there are no tricks played upon shar by the astute miner; for "for ways that are dark and tricks that are vain" the western miner is at times "peculiar." One of these tricks is what is known as "salting'' mines or ledges; that is, by various means and ways introducing into the mine or into the samples taken from it, certain rich minerals which do not rightly

elong by nature in the mine or property, in order to raise the value of the mine in the eyes of the investor or expert. When samples are taken from such a tampered-with mine the values and results must be accepted cum grano salts, with a very large grain of salt indeed. Whether this classical allusion be the origin of the word "salting" we do not know.

"Take care you ain't salted" is the advice to the inexperienced investor or novice expert. So clever are the miners, that cases are on record where even a most experienced expert has been taken in, and comparatively, or wholly valueless properties sold for large sums, the purchase followed later by woeful dismay and surprise, when dividends were called for and did not appear.

Gold mines of all others, are the most easy to salt, hence the precaution in these days is timely.

Whilst a mining engineer or expert can hardly prevent salting, with care he can, and ought to be able to avoid being taken in; to be forewirned is to be forearmed.

On entering a mining camp in the far West, especially in the more remote outlandish districts, an investor or an expert, may consider that the whole village, from the ho el bell-boy to the mayor, (who, by the way may be the principal saloon keeper) is in league against him. Directly he arrives, everybody in town wants to know his business ; on this he should keep as mum as possible, and, if he can, throw im-

pertinent inquirers off the scent. The idea is, "Here is a capitalist to fleece and an expert to delude."" Every one, too, has a "hole in the ground" of his own to present. Should they get wind of the particular property in view,

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there are confederates and middlemen anxious to share the spoils. Moreover, it is considered to the general credit of the camp to sell a mine, be it whose it may, good or bad, and if you mention any property, you will invariably hear it "Cracked up." The eastern "tenderfoot"" is somewhat of a "sheep among wolves" in sucha camp, The expert, too, is ata certain disadvantage on entering into a strange mining camp, not being familiar with the local conditions, Ores for instance in one section or region are not always of the same value as similar ores in another, the rocks may look new and strange to him, and there are a hundred local conditions known only to the resident miner. It would be well, when possible, for an expert, before passing a decided opinion on an important property, to stay around in the vicinity for a while till he knows the " hang of things."

On his way to the mine there will be plenty to fill his ears with the untold value of the property he is about to examine, this friendly duty is not unfrequently performed by an officious middleman. To favor and "soften up" the expert's mind and heart and make him" feel good" toward the property, attentions of all kinds are showered on him. He is driven about town like a nabob, and if he shows a weakness for a " wee drappie,"" champagne and whiskey are at his service ad /2b,, as judicious preparation for the coming examination, It may be observed here, that attempts are made sometimes to " salt' the expert as well as the mine, not merely by befuddling his brain with intoxicants, but by offering bribes, and as an expert is often not too well off, the latter is a grea', temptation.

We will now suppose, after this ordeal, he goes to the mine with the superintendent or miner. All may be, and we may say generally is, honest and square, or it may not. The expert looks over the exterior and surface signs of the property, studies the outcrop of the vein on the surface, its probable surface continuity, the advantages and disadvantages of the situation of the mine, its proximity to railroads, smelting works, markets, etc., and then enters the mine in company with the miner. As a rule the latter will naturally point out to him the richest portions and ignore the poorer; sometimes he excuses himself from taking him down into the latter because it is dangerous or full of water. If full of water the expert if possible should have it pumped out. He may suggest here and there, that such and sucha spot would be a good one for the expert to take his samples and so forth. The expert of course assents to all he is told,

but with one eye open, and does not stop to take any samples for assaying until he has seen the whole of the mine, then he requests his companion to go out on the dump and smoke his pipe there, as he insists upon having no one with him in the tunnel when he is taking his samples for assay. He will be inclined to rather avoid those particularly favorable spots suggested to him by the miner, as probably giving too rich an average for the general run of the mine, or as not impossibly being " fixed" for him. If he suspects the latter, he will take a sample or two to see if the mine has been tampered with, taking a little of this out on the dump crushing it and washing it in an iron spoon, If a very astonishing amount of gold colors show up, his suspicions are aroused, The judicious miner does not generally want to salt too heavily, for fear of the enormous results exciting suspicion, but despite his care he nearly always salts a little higher than he intended. Ina mine where the rock is hard, a miner may salt by drilling holes and inserting mineral or ore and disguising the hole. In loose ground or one full of cracks, a shot-gun loaded with a moderate discharge of gold-dust will do the work. The skill of the miner in this case lies in his choice of a spot where he thinks it probable the expert will take samples, or in coaxing the expert to take samples from such ground, In hard ground the expert may avoid such salting by having the work blasted out in his presence till a purely fresh, virgin face is shown and then taking his sample. These precautions are not necessary under all circumstances, but only in such cases where the expert has a suspicion that there is an attempt to " put up a job" on him.

After getting his samples, and as many as possible, he will sack and seal them then and there in the mine, and never lose sight of them till he has expressed them to his own home.

Sometimes a mine is so timbered up, that sampling is difficult. Now as they go down the shaft, it may be the expert remarks "I should like to take a sample in this shaft, but it is so timbered up that I don't see how we can do it without ripping out some of these boards." "Why of course, so you oughtter" says the miner, "and see here, I think this board is loose." Now beware lest that board was purposely loosened and behind it the ground is salted.

By taking a great number of samples at comparatively close intervals, provided afterwards the samples are not tampered with, the expert is less liable to be deceived by salting, than

if he took very few. A mine cannot be salted all over from end to end if it is a large one, only at judicious intervals, and it will be hard if the expert does not escape some of those intervals and get some true samples,

Besides taking his regular assay samples by cutting all around the walls, roof and floor of the tunnels at intervals of five, ten, or twenty feet, according to circumstances, crushing, and quartering the debris, and finally sacking and sealing his sample bags, he should occasionally take a" grab sumple," or a Dit of rock at random, or a small sackful from the great mass of his sample, and put them in his coat pocket, and keep them on his person, to act as.a reference in case of any possible tampering or accident to his samples whilst in the vicinity or in transit. He should also take bulk samples, good sized chunks of uncrushed rock which should agree with the assay results of his quartered samples.

A disadvantage an expert is under in a strange camp, if he cannot take his own assistant with him, is, that he is very much at the mercy of the miner, if any hard work has to be done, such as blasting or hard Hanlin Whilst engaged in such work the miner, if he pleases, has many chances of scattering around a little gold-dust on the rock of the vein or the loose dirt of a placer.

Whiist gold-dust is the favorite medium for salting a gold mine, chloride of gold is sometimes used. The latter, however, is rather a dangerous and barefaced trick to try on a competent expert,as its quality can readily be detected by the chemist, it being soluble in water. Ina case of this kind that came to our knowledge, an experienced expert had examined a certain mine and condemned it. Later, the owner who was an honorable man, asked him if, as a special favor, he would re-examine it, as in his absence the assay values from the mine had of late shown much better results. The expert reluctantly consented to do this, though contrary to his general rule. In going along the workings he noticed here and there on the walls, certain patches and streaks of clay or mud, he had not observed on his first visit. Guessing what they were, he casually observed to the miners, 'Seems to have been raining in the mine since was here."' However to the great delight doubtless of the miners he took several samples of these, and forwarded them to a reliable chemist. The latter pronounced them chloride of gold. This of course gave the salting scheme away as chloride of gold does not occur free in nature, much less in a mine. The owner of the mine was exceedingly

angry when he learned what the miners had done without his knowledge or connivance, The men themselves being commonly more or less interested in the sale of a mine, are apt to try and salt it without any connivance of the owner or superintendent. We heard of a case in the San Juan district where a mine that was fairly good was about to be examined, This mine carried occasionally specimens of the very rich ore, called ruby silver, Not satisfied with the fair, natural richness of the mine, the miners must needs import into the hole, quantities of ruby collected from other mines in the district, whose men were of course in sympathy with the scheme and probable sale. This was acting without the knowledge of the owners,

Salting Gold Placers,

Although a gold placer usually covers a very large area of ground, it is possible to salt it. Usually a miner shows up his placer by opening up pits at convenient intervals, so as to cover the property. Nothing is easier than to salt these pits with gold-dust. Consequently whilst an expert wiil examine these holes and pan the dirt, he should be on his guard, and insist, where possible, on holes being freshly dug in his presence. Even then he is not safe. Generally in a placer, by the cutting of a stream, sections are shown sometimes from grass roots to bed rock, From such he should take and pan samples at different levels in the exposure, this too, privately and without too much supervision of the interested miner,

Assay Samples,

Salting

This may be done in several ways. If the expert is imprudent enough to allow a miner to accompany and assist 1imin breaking down or crushing samples or panning them, then the infusion of a little gold-dust is easy. Again, after the expert has made up, sacked and duly sealed his samples with wax, should he leave them anywhere within reach of the miners, they are not wholly safe, for the miner may insert the point of a fine syringe containing gold-dust into the bag, or he may make a bread mould of the wax seal, open the sacks, and either change the ore for richer, or infuse some gold-dust. Changing of samples for others is not an uncommon trick. The expert cannot watch his samples too closely. Heshov' sack and seal them on the grand, sleep

with them under his pillow if need be at night, yet even then cases have been known when the wary miner has succeeded in extracting and changing them for bags, to all appearance exactly similar. The samples are never safe till boxed up and expressed and on the way to the city address. He should never fail, as we have said, to have partial duplicates of these about his person.

If the expert wishes to assay the ore at a friendly assay office near the mine, whilst he is grinding down his sample to dust, an innocent looking miner may loaf in, and whilst watching the operation, accidently upset the ashes in his pipe over the sample. Probably these ashes contain golddust, and we might here observe that a single grain of gold smaller than a pin's head may materially alter the results of an assay.

Some years ago an individual who had succeeded in booming acertain placer district and getting up an excitement and a rush, constituted himself as a referee, and professor ; and when miners brought samples for his inspection, the were always found to be very rich in gold. But simila samples from the same spot if uninspected were somehow invariably barren. The wizard's inere look seemed to change

the sand into gold, until it was found that he concealed in

"

his finger nails "which were taper" not wax, but fine particles of gold. Hence Midas-like whatever he touched he turned into gold. Whilst the salter may lay traps for ihe expert, the expert may sometimes lay traps for the salter. An expert, who had reasons to suspect a certain mine he was examining had been tampered with and guessing there was a likelihood of an attempt on his samples, after securing himself with duplicates, left his samples exposed on the floor of his room at the hotel, then went out and hired a reliable Mexican boy to watch his room and report to him immediately if he saw any one enter it. He had not long to wait. At dinner the boy tapped him on the shoulder, and he went to his room and caught the miner in the act of tampering with his samples.

Sometimes miners, if wealthy enough, will go to great expense to salt a property. Some miners took a couple of well-to-do eastern capitalists to a certain placer, panned the gravel before their eyes, and showed up wondrous colors. The investors having been warned of miners' ways, refused to entirely swallow the bait, but told the boys to go ahead and develop the property, and if at their next visit, it showed up as well as the pans did on this occasion, they would

buy it. When the easterners were gone, at cost, of several thousand dollars they built a flume, put in a hydraulic plant, and gathered a pile of loose dirt to wash down the flume, where the go!d is gathered upon quicksilver. The "sharks " raised $50,000 for a gold-dust fund. This dust was run evenly over the quicksilver so that when the capitalists returned, there was everything to show an enormously rich placer-ground. The capitalists insisted upon clean-up after the first fortnight's run, which added so much more joy to the sharks. This time the bait was swallowed whole, string and all. The capitalists paid down promptly $250,000 for the ground. The sharks left the country. Ina few weeks nothing could be found but the amalgam of the sharks.

An ingenious trick once baffled some experienced experts and came very near selling a mine. The mine was a well developed one and had done great things in its day. It was claimed that at the face of the turned, or where the workings left off, there was still a fine showing of ore in nlace to go on with. The experts found it as stated; on the face or end of the tunnel there was a fine showing of ore, and the probable amount in place and for the future was July measured up and estimated. It leaked out later that this block of ore was only thin screen purposely left, all back of, and behind it, having been carefully worked out and the opening for the miners ingress and egress skilfullv concealed. The mine was re-examined, the cheat discovered and the reputation of the experts saved as well as many thousands of dollars from the pockets of guileless investors.

This brief sketch of some of the ways of some miners, for some regions and properties, would give an unfair idea of some mines and miners as a whole, if it were supposed that all miners are given to salting, and all properties for sale are beset by a network of dishonest devices. On the contrary many, very many, miners are as straight as a string and hundreds of properties are to be examined without fear of tampering. But it often happens that a miner, who in every other relation of life, is as honest as the day, draws a line, when it comes to the selling of a mine, which he considers "fair game."

But, as elsewhere the world through, honesty pure and simple is the right policy, and in the end would be found the best paving one. For the notorious dishonesty connected with mines (much more common in the past than in the present) scares away capitalists from investing, whilst

if truth and honesty were maintained, money would roll in freely,

One lesson at least may be learned from what we have said, and that is, that if in some cases a professional expert is ever taken in, what chances has a capitalist, ignorant of mines, to buy a mine on his own examination? What man ignorant of horseflesh would venture to buy a steed from a professional horse-jockey, without taking with him a friend who is knowing about horses ?

How much more so in such a difficult and delicate problem as that of purchasing a-mine, is it the duty of an investor never to purchase or induce his friends to purchase a mine, until he has employed the services of a competent expert to previously examine it. If the expert's fee should amount to a few hundreds, and after all he should decide on condemning the property, it is far better for the company to entail this expense, and perhaps lose this small sum, than to involve themselves in the loss of thousands of their own as well as other people's money in a bogus, worthless, or wildcat scheme,

Chapter Xv.

Prospectors' Tools And How To Sharpen And Temper Them.

The principal tools a prospector takes into the field, are picks, drills, hammers and sl.ovel.

A prospector, especially when climbing mountains, likes to be as light-handed and unencumbered as possible.

For his trip as a whole, ite may carry several different tools packed on his donkey, but when he has arrived at a locality, the vicinity of which looks likely, he leaves most of his heavier tools in his temporary camp, or near to where he pickets his pack animal. He makes a short excursion up the mountain for a general reconnoitre, armed with nothing more than a light prospecting pick, weighing not more than three or four pounds. This little pick is about ten inches in length, with a handle about fifteen inches long; the longer portion is sharpened into a pick, and the shorter ends in a square faced hammer. We recommend a square sharp cornered face to the hammer, in preference to the bevelled

face, as the sharp edges and corners are better adapted for breaking rock than the rounded or bevelled ends. This prospecting pick or geological pick and hammer, should be all of good steel, with a good sized eye to admit a springy handle of hickory. See Plate XCVII, Figs. 1, 1, 1. y Armed with this little weapon he climbs the hillside, hunting for " float" or for rusty outcrops of ledges. Loose pieces of rock he cracks open with the hammer end, softer rock in place he explores with the pick. '" When

I am climbing over the hills," said an old weather-beaten pros-

pector to me, "I want nothing

but my little pick, then if I find

anything likely 'in place,' I

mark the spot, and go on, and

at noon I come down to camp, or to where the 'burro' is feeding, I take up my heavy digging pick and shovel and 'open up'; this will occupy me till evening

at least, then if I find there is a

Pirate XCVII. ledge worth more thorough expioring, I leave my tools by the hole, and next morning bring

up the drills, hammers and blasting outfit. But the first thing I would advise a tenderfoot, is to get his eve trained, trained to looking for float and observing mineral signs, trained to the whole business of close observation. Why! I myself, old hand as I am, after being away for some months about town or looking at other things, can't get my eyé in and down to it for two or three days; then it kind of comes natural.

" You must have an eye for float and rocks like an artist has an eye for color, and a musician, an ear for music. A tenderfoot had better go along with an old hand for a few days to get into training."

Picks and Hammers.

Description Of Tools, Picks And Drills.

Picks and drills are the main tools that need sharpening and tempering. The kind of sharpening and nature or degree of tempering depend upon the kind of work or kind

of rock to be worked, whether hard or soft, loose grained or fine grained, siliceous or clayey. Drills, for example, would have to be differently sharpened and tempered for hard vitreous quartzite than for soft sandstone or hardened clay. The same remark applies also to picks. Picks may be double pointed or single, or with a hammer head called a poll, if it is to be used for breaking rock. The main points ofea pick are, strong cutting tips, stout eye and a tight handle. The little prospecting pick is made of the best steel throughout, but in the heavier pick, the wearing parts are the tips, which should be replaceable. An all steel pick is liable soon to be shortened up aud useless, whilst the iron pick eye, a 14 inch length of best iron, gives long service by welding on tip ends, whenever desired. Professor Ihlseng, in his '' Manual of Mining," as also Mr. George Andre, in his book on " Rock Blasting," give excellent descriptions of tools used as well as the mode of sharpening and tempering them; to them we are indebted for many of the details of this article, and to their works we refer the reader for further information on this subject. "The picks are sharpened to form on an anvil, and commonly drawn to a four sided pyramidal point, for hard rock, and a slim taper for fissured rock, and a bluff taper to cut crisp ground, and to a chisel end for chipping the ground. The eye is oval and well surrounded with metal. All the strain of the prying falls on the eye, which must be true and stout."

"The Grill is a bar which has one cutter edge and one hammer end. It is of round or octagonal steel. Drills may be of various lengths, from a foot to four or five or even more feet. For prospecting purposes two or three medium short drills from two to four feet are generally enough, as the prospector's business is rather to find than to develop. In beginning to drill, it is common to use a short thick drill, with a stout 'bull edge' rather than a thin, tapering one, especially in hard rock; smaller sized, z. ¢. narrower drills may be used for increasing depth.

"The rock drill consists of chisel edge, bit, stock and striking face. To allow the tool to free itself readily in the bore hole, and to avoid introducing unnecessary weight onto the stock, the bit is made wider than the latter. In hard rock, the liability of the edge to fracture increases as the difference of width ; the edge of the drill may be straight

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In

or slightly curved, a straight edge cuts more freely than the curved ; a bull bit for hard rock is generally curved, a straight edge is weaker at the corners than the curved. The width of bits varies from 1 inch to 2% inches. Figs. 1, 2, 1a, 2d, Plate XCVIII., show the straight and curved bits and angles of cutting edges for use in rock. The stock is octagonal in section. It is made in lengths varying from 20 inches to 42 inches. The shorter the stock, the more effectively it transmits the force of the blow. To insure the longer drills working freely in the hole, the width of the bit should be very slightly reduced in each length. Diameter of stock is less than the width of the bit generally by 3% of an inch. "The smith cuts up the 'borer' steel bars into desired lengths to form the bit, the end of the bar is heated and flattened out by hammering toa width a little greater than the diameter of the hole to be bored. The cutting edge is then hammered up with a light hammer to the requisite

Oi!

Drill in hole

c in rock, Twa COLvierv ENGinere ANO MeéraL Miner ot

oh Fe

Plate Xcviii.

Forms of Drills.

angle and corners beaten in to give the exact diameter of the bore hole intended. The drills are made in sets and the longer stocks will have a bit slightly narrower than the shorter ones for reasons already given. The edge is touched up with a file. Heavy hammering and high heats should be avoided. The steel should be well covered with coal, in making the heat, and protected from the raw air. Overheated or burned steel is liable to fly, and drills so injured are useless until the burned portion has been cut away. Care is required to form the cutting edge evenly, and of the

full form. If the corners get hammered as in Fig. 3a, Plate XCVIIL, they are said to be 'nipped' and the tool will not free itself in cutting. When a depression of the straight or curved line forming the edge occurs, as Fig. 34, the bit is said to be 'backward' and when one of the corners is too far back, as Fig. 3c, it is spoken of as 'odd cornered.' Either of these defects causes the force of the blow to be thrown upon a portion only of the edge, which is thereby overstrained and liable to fracture."

Sharpening Tools.

Professor Ihlseng in his ' Manual of Mining" says: " The best fuel for blacksmithing may be a slightly caking coal, giving flame and high heat. Coke is hotter but harder to keep fire in. The. fuel should be as free from sulphuras possible. White ash coal is better than red ash; sulphur makes the iron hot short, and tends to produce scales. The coal should be clear of shale or slate, for they fuse and make a pasty cinder that is annoying."

A prospector away from civilization may have to use wood ; in that case he should use chips, and-blow them with a portable bellows.

The prospectors who try to get along on as small an outfit as possible usually take one to three blasting powder cans and cut the heads out of all but the bottom one, and one head of that must be cut out ; these they place one on top of the other to make a furnace. They punch an inchand a half hole in the side of the bottom one at the bottom for draft and to put in the points of the tools to heat them.

They use charcoal for fuel and then a chunk of steel or railroad iron about 6 inches long serves for an anvil. Some take a small bellows and anvil with them. For tempering drills they give the drill, when red, aplungein water. After two or three rubs on wood, to brighten it, they hold it up to the light and watch it until it takes on a straw color. Then they dip it in water again. For picks a blue color is the most satisfactory in general.

Steel is a compound of iron and carbon and its homogeneity and presence of carbon imparts to it a capability of hardening and tempering to a degree depending on the temperature of the heating and subsequent cooling. As the amount of carbon increases, the melting point of the iron decreases, and this greater fusibility reduces its welding quality.

"A steel is called ' hardened' when it has been suddenly cooled and thereby become as hard as possible. This is owing to the presence of carbon, for pure malleable iron is not affected by the operation, while both steel and cast iron are to a marked degree.

'The operation consists in forging the steel to a certain degree of temperature, and then plunging it into some fluid which abstracts the heat from the tool. The quicker it is done, and the greater the difference of temperature, the harder is the tool. Either water or oils used; both volatilize at a temperature much below that of the immersed tools, so the hardening takes place in a vapor; oil generally produces the best effects. On the first plunge the metal is chilled

and coated with soot, after which, a slow process of cooling takes place.'

Tempering,

" Tempering follows hardening, whereby the steel is subjected to a subsequent lower heat, which softens it, and removes its brittleness. When the hardened iron is slowly reheeted, its surface gradually assumes phases of color, beginning with a light straw, passing through shades of yellow, brown, purple, blue and red. At a cherry-red heat, the original color before hardening, the effects of the chilling are practically removed.

" Tempering consists in carrying the second heat to one of the above mentioned colors, according to the amount of. the brittleness to be annealed. This depends upon the use to which the article is to be put. A second stage of the operation finishes the job. The aforementioned reheat, goes on a little way beyond the desired color. The tool is carefully plunged part way into the water or oil, till the disappearance of the steam indicates that it is cold, when another portion of the distance is further immersed fora moment. The tool is withdrawn, the scales rubbed off and the heat of the remaining portion draws to the edge, until it has assumed the proper tempering color. It is then thoroughly cooled. The idea that the steel is cooler at a blue, than at a yellow, in final drawing, is erroneous; for more of the heat is conducted from the red portion to the point, than it radiates to the air, and the first heat to the edge only gives a yellow; with more, it becomes purple, and so on. Hardened drill and pick points are treated in in this way, 4" of the end being heated to a yellow; and, in thirds. the tempering is proceeded with as above.

"Care should be taken that the plunged too! while tempering, be not held too long a time at a certain color line, as it has a tendency to break at that point. The tool should be slightly waved in the water. 'Pieces' which are to be tempered throughout must be allowed to soak, ¢@ ¢, become uniformly hot, before plunging.

"The proper color fora given ground, is only ascertained by experience. Generally speaking, the picks and drills are stopped at a 'straw,' if intended for hard ground; at a blue, for mild ground. The toughness of the steel should be preserved as much as possible, therefore select the lowest color compatible with the service to be performed. A high carbon He se given a lighter color than steel of low carbon.

" A pick is made of a square iron ber 14" X 14" heated at the middle, and then struck endwise, till about 1%" across. This spot is softened and at red heat, cut open, and swelled bya drift to form the eye. This is then slit at the ends, and softened, while a 6" length of pick steel is being heated. When ready, this steel is tongued into the iron, and hammered, reheating with borax, and a hammering complete the weld, after which the picks are sharpened and tempered, no signs of the weld should be visible."

'' Pick-steel " is a special steel that can be had in bars 14" or 144" & 3" or "and used only for tips.

Steel bars for drills come in lengths of about 14 feet each and from %" to 2" diameter. The American "Black Diamond" brand is a favorite. The bars are cut into pieces as long as can conveniently be used, ¢. g. 30" and 36". The bits are wider than the tool, to prevent it sticking to the hole. They are widened according to pattern, so they can " follow" well. The first drill has the widest bit; the followers narrower ones. In hard rock the flare is smaller than that in soft rock.

"The temper is a lighter color for hard than for soft rock. If the edges of the returned drills are cracked or broken the steel is too brittle, and should be made softer or other coal used. Ifthe edges blunt much by wearing round, they are all right, though a harder temperature may give them longer life. Cast steel borers are never heated above a cherry. They are annealed at the striking end."

Practical Sugg2Zstions And Points By A Blacksmith.

A Ber must have something to act as an anvil,a

hard pebble wont do, he can carry a small anvil or a chunk

of railroad iron, A small hand bellows or even a portable forge worked with a crank will make his outfit complete. The following practical hints I picked up from a blacksmith whilst watching him at work tempering both picks and drills for some prospectors, He said: "You must temper your drill according to the character of the rocks.

" For hard rock, use a short thick edged ' bull bit' which will stand a high brittle temper such as 'straw.' For picks, alight blue color is a good temper, rather than 'straw ' which is too brittle. Cherry red is the heat of your bar, not hotter ; laying this on the anviland hammering it well all over gives it toughness. If blisters show on the steel you must hammer it over again. By occasionally dipping your hammer in water and then striking with it, you get the steel down to a fine grain. When you are dipping for tempering, put the point in the water, that cools the point, and the heat runs the color down to the cool point ; when the color reaches the tint you want, then is your time to cool off quickly. The color progresses from a white or pale straw to copper color, to blue. Copper tint is a good one to stop at fora drill,— blue, fora pick, The right moment to stop and cool is just at the turning point from one color to another."

He took a piece of steel, heated it to cherry red, laid it on the anvil and pounded it Hepes with his hammer all over, to toughen it by blows, occasionally na Ae his hammer in the water to "water temper" it: this further toughens it, by partially cooling it. Now the bar was again put in the fire and heated to a cherry red, care being taken not to keep the bar too long in the fire, as that would tend to take its toughness out, or produce blisters. The bar was plunged about an inch into the water, and then rubbed against a brick, to show the colors plainer. These passed from the point upwards, gradually through the colors we have mentioned ; to arrest it by suddenly cooling off at "straw," would make it too brittle for ordinary drills, except a " bull drill." Now the "straw" turns into a copper hue, a good point to cool off fora drz7v. Now it passes into a blue, at this point it would be well to cool off fora pick. The edge of drill is almost of secondary importance to the sharpness of the projecting corners ; when these are gone, the drill is used up, and clogs in the hole. Some rocks like sandstone will, by reason of the quartz in them, wear off the corners very rapidly, others, like limestone or granite, less rapidly.

Another blacksmith advised me not to dip (as is commonly done) the point only an inch in water as it is apt in use to

break at the water line, but plunge it a// over in the water. "Who shall decide when doctors disagree ?"

A prospector should take with him a regular blacksmith's hammer for sharpening, as well as the 4 or 5-lb, hammer he uses for striking drill or the rock.

Chapter Xvi.

Some Elements Of Mining Law Relating To Prospecting.

A prospector would do well to as fr himself with a few elements of mining law, so we will give a few samples of Colorado mining law for his benefit.

Extent of Lode or Claim—The length of any lode may equal, but not exceed, 1,500 feet along the vein.

Dimensions.-—The width of lode claims in Gilpin, Clear Creek, Boulder and Summit counties, shall be 75 feet on each side of the center of the vein or crevice.

Certificate of Location—The discoverer of a lode shall, within three months from the date of discovery, record his claim in the office of the recorder of the county in which such lode is situated, by'a location certificate, which shall contain ;

ist. The name of the lode. ©

2d. The name of the locator.

3d. The date of the location.

4th. The number of feet in length claimed on each side of the center of the discovery shaft.

5th. The general course of the lode as near as may be.

Discovery Shaft—Before filing such location certificate, the discoverer shall locate his claim by first sinking a discovery shaft on the lode, to the depth of at least to feet, or deeper if necessary, to show a well-defined crevice.

Second, by posting at the point.of discovery on the surface, a plain sign or notice containing the name of the lode, the name of the locator and the date of the discovery.

Third, by marking the surface boundary line of the claim.

Staking.—Such surface boundaries shall be marked by six substantial posts, hewed or marked on the side or sides of which are in toward the claim, and sunk in the ground, to wit, one at each corner, and one at the center of each side line, Where it is impossible on account of bed rock, or precipitous ground, to sink such posts, they may be placed in a pile of stones,

Open Cuts —Any open cut or cross-cut tunnel, or tunnel which shall cut a lode at the depth of ten feet below the surface, shall hold it, the same as if a discovery shaft were sunk thereon, or an adit of at least ten feet along the lode from the point where the lode may be in any manner discovered, shall be equivalent to a discovery shaft.

7ime.—The discoverer shall have 60 days from the time of uncovering or disclosing a lode, to sink a discovery shaft thereon.

Construction of Certificate—The location certificate of any lode claim shall be constructed to include all surface ground within the surface lines thereof, and all lodes and ledges throughout their entire depth, the top or "apex" of which lies inside of such lines extending downward vertically, with such parts of all lodes or ledges as continue to dip beyond the side-lines of the plane, but shall not include any portion of such lodes or ledges beyond the end lines of the claim, or at the end-lines continued, whether by dip or otherwise, or beyond the sice-lines in any other manner than by the dip of the lode.

Cannot be Followed.—l{ the top or "apex" of a lode in its longitudinal course extends beyond the exterior lines of the claim at any point on the surface, or as extended vertically downward, such lode may not be followed in its longitudinal course beyond the point where it is intersected by the exterior lines.

Proof of Development.—The amount of work done, or improvements made during each year shall be that prescribed by laws of the United States.

Placer Mining Claims.—The discoverer of a placer claim shall, within 30 days from the date of discovery, record his claim in the office of the recorder of the county in which said claim is situated, by a location certificate, which shall contain :

ist. The name of the claim, designating it as a placer claim.

2d. The name of the locator.

3d. The date of the location.

4th. The number of feet or acres claimed.

5th. The description of the claim by such reference to natural objects or permanent monuments as shall identify the claim,

Before filing such location certificate, the discover shall locate his claim ;

1st. By posting upon such claim a plain sign or notice containing the name of the claim and of the locator, the date of discovery, and number of acres or feet claimed,

2d. By marking the surface boundaries with substantial posts sunk in the ground, one at each angle of the claim.

On each placer claim of 160 acres, not less than too dollars' worth of infor shall be done by the first of August each year, and upon less or more ground a sum in proportion,

PAGE Algonkian Epoch csee :- iaewneekiausececkuas 26-27 Alteration of Rocks and Ores gy, 161 Andesite Lava 23, 35, 57, 94, 124, 127, 137, 141, ISTE ADOR ENG BIGE LING cecciccpcccascewssensees cestesecsen 171, 172 Archean Age pcuebbeetenens esebwesswees 18, 20, 21, 39, 96 Argentite Ore... cece cece ceeee nee ccee cre reeeecees 63

SN Wak aeks cake eons bG4c KEES VEC se keéedeebhenssadebendecaar

Aspen Mining Camp 75, 83, 85, 88, 99, 165- 74 PUM ic es cbse ticcccteeveeeckeess cenebecretenn déachemnens can 51 PAIGE oon 55005 hC LAE RKS DAA e9 5D 0 dSsNss Oud Ceeenneeee 106, 110 Banded or Ribbon Structure 2020 seeees-eeeeeeee 87 MORE ckceebscaciakeccuaccanses as RObme ngs GSMO wie a 52, 76, 161 BMORIE EBVE scree scbi a ce cevecccontvecvsance 34, 35, 57, 58, 94, 112 ERED PEE ce hns v cc encaceteccnses senceceucnee eueneuban 113 BIT GND nce ood oc ccencceneccseviasencnsceshevesons 62, 95 Blanket Deposits... ccc. vecccesss eee pee eee 73,75, I51 OP CRONE ROR Reavccsnswentounesenseves 'Rene deren tine 88, 171 EMME" ¢scthbacthahwesiveeedevese ss Seacensesisuneene 112 (CRUG; RAMORIODE bcs sn ecdsnudeccacccdesaveedsascece 22, 39, 156 Booming" Mines (ecighihavedéhuscbstvaeys 173 Boulder Mining Region 20, 26, 73, 93, 117-123 DWC EIUG) Kascvens cavaces tien. odes tela ss ebpurebacneesceeas 88 CaleHe co scccecee SeRORREEG MELE Shud Ses one eRe eRbeKeRTebaeres 51 COROT vineeg ented sso eens ceucceses 34, 105, III, 112, 113, 115 COMPA soc keuee.ccbccevecdéceabesebsowetewcdicusne 21, 28, 4o, 48 WRVOUM eins tc cuiecess ietaceene wien b teers wowecoee¥Q)-90)-O8 Carbonates 'KEEBLE ANS EN RO RS RES ROE E RSE R NERS 65, 66 Carboniferous ceccecnesee 18, 21, 31, 42, 43, 49, 156, 168 GOVES Gt CAVIRES... . occ cecncwcccucccccescccccvens 162, 163, 169 GRIPE adits eal kGadc veer sna chhencdvees seuadiedcvuaweereeke 64 GNLINS Saree (Rene. cbdvadascoanedecbades ceedeo ae Cane ve brent 51 CERRB URE haa io kis hak icn wees ck heksn en acenaskeieaeeienned 35, 132 SON ee soa ck Sas hdc wccem Badbepebewosey sae auetaeaees 23, 31 GOBIOCI MING. 05 5 ccc ccs ccnenvonsenecesaace par g2, 103, IIO Contact Ore Deposits 49, 73, 94, 151, 169 GUDUGE cciewrctsadscecie- Cisdersenetensaenanswans 60, 61, 65, 126 COMEIEV TOO: 6 ceicn caudedad eocene wesdned cebee bese heme emben 97 CeGee NNR COIN, 5. -cncwcene sumac csaduacusegescngsgsacs 126 GPR OU ORG ceeibiavcccber ceeds vives cecbbsesceaseancn 23, 33, 45, 96

Cripple Creek Mining Region 12, 35, 94, 128-151 GEOR CUE, ccavecn scdenctecdbcececcnbusesesess eicseus IOI, 102

¢.

204 Index,

, PAGE Cross Veins... 2-22. 1006-2 nn en ne conn nn ene enn ee cece eens -86, 87 Dakotah Group 0 0-20-22 - ener eee ence eeeee- 23 Decomposed Ores 202 1+: cece ooo cece ween + 2-92 DONdrites oe cs os sees sebnccesee snr coeeneress ae Oe eee 147 Deep Leads ... --- sn eceecnten- Wallet owedesanweeneue -III WOVORNIONy .cc0c nde ncd nce ne wecewy geclnsaceemadate ene deeeee: 30, 42 PSA UTN seco ne Fak pice nal ve yabe elses ecawstnawenncasce dara DIGHtO Maio ooo ares cw wine Scenes weds Sulniseidie Simones sacicmes 55, 94, 168 Wi vader: GesicancessewndacenesanbentaGescys - abe eens 85, I0i, 102 DIGIOMICG oc oo 0s cvs con euscondtanasewagesnedaneteenmense 21, 51 DolOMitization=\8is002e Sees sar cne sue cacss sees wbeeccese 75, 170 PT tire oe aoe os wide So eco Somme: noise meas esalene orm agen 76, 195 DY ROSS 5 ncein ks cee canes - cccmensese -50, 93, 94, 100, aoe 149, 154 BRU OHOMEIGIN pvicirs baa cha nese Sao eices eked heanns pet eawea ce oe 25 EGucaow Of ProgpectOri..<o's cisco ches tend wig on naeeeenanedouace § BE UBLVE. INOCRG bc cs.wncans cbc ddewne dpa ncs ba 8bee veneer heweseae 57 PLPUPUVEG ROCKS. - veenndsutdiacnstabotevosbessesaseend 57, 94, 98 DUTCH WINCR ss sd aice cn ono nein debian sus dew wones Seca nes hear 30 EOIIGING: MINCSs ccs:cdncdin dn dewsdwcsiceeuqaecseabnennniss 174-185 POUR coat ead sm we aCe adlaw dy we wa pie sarsonk 68-71, 79, 80, 8I, 93, 153 POMBO cacecee ancien Lown gases cen endeetTaaaeges aasebd pe k ee oe 50 Fissure Veins 0+--5-ace- 48, 77, 87, 90. 117, 123, 131 PRIOR ap aewe eek Uncishee scans autem elke 13, 14, 88, 144, 145, 147 POUR is smpecsss eens ba nved esse S0heusitauceaeseare renee 28, 68, 8r BOSSIIGM coc castuntadewce eect Sam's 23, 29, 30, 32, 33, 34. 38-46 BreesMilling Ores. coc cnsebescuesicckacticcttue cheese 88, 95, 181 GAIENO aha pao sie we Silealsee bh cameos we.,Ee sedis 8, 98, 156, 161, 181 OER Sa) o SCE Re NGhe wae pains SDAweeu Scene cece smeencaee sans 139 Geography, Ancient New wee cites SEncaee eee 29, 33 GOClORY TIGIOTICAL,. ccs esceeisenesebseciddontgcsucteayeuee 24-46 Geolopical Ages. co50 cs cceeice ceelncecceebhscd ecg senesced 20, 23 Geological Sections Pree rey re eames wes 17-19 Geological. Traitting 2. .0censceewewae once eceees caw ol Acs ae Bate 15 Geological Works s-2c-eece0005 ese e aaa ees a 15 GIAGIAIFACHONN.. 3. 2c ows cectedetcetiesensdtacsteanees 116, FEO GIAGION NOCN cc nadaanenaxdwdessbeas wet ee abectead! exes Byers

GiGISS ee ot oes Owscame wa e bac ot bee saan Sarees cee a es

GHANE Canyons yas ass ccaw see ees ies teowsaeeetess -Ig GPANtCie sok a ceo cao ule ae tneee we SaSu eee Saas een ee Reser 52 UR CONV ODED oa soci nates cee en Knestagesceeeterds eet tater 22, 31 CUAHIION ROPION. oct vc. cevaseccsitdutccuensucc ose setiens ldap 96 COVE: Cac chide ce hGue wedeblactte SeUUSsicee ses Sous DApWAMwES Cee 52 Historical Geology Cekehewwrso ea coisa cee Musee eae ed Hornblende Sicldvchiaa -aGtele Stu a as Sieeia we ce ee ae ae 51

RUONBR Ss arch Gxon Cees winewcus enema adele ects asain vor aletante ere eee PEVOTHUNENC os ch wh vichn-cbnuwo bs cabbie <auwerescseceleaneneseee 113 FONGGUG ROCKS ccc siicnseerdiacCindcteawie boa ele-wia ease soe ae OAS

Index, 205

Page

Impregnations +-e-0+- eee 82, 86, 145, 164 WHlGAtlONG: oni. si:c cane ceewteeneseaede sseenseseee 78, 79, 143, 144 Intrusive Rocks. . ..62cc..c.sccccsectesecscenconassanss 54, 72, 94 Joints + ee eee ee eee 69-71, 82 Jurassic 2 eee ee eee eee eee ee eee eee 25, 44 MAQUI GN venadiowaeodNedesceKeksduedegsis si edebeeeakamees amy 161 Kootanie Region Le Se amd-gives Ge Us aNeéis emnees 27 LACCOILGR: oar ved cece bdnsdcenseeccstncencebecedeesen rene: ws 54 Laramie Group. nincec-seoeeeess Ver bresteeeeegam 23, 32, 33, 46 iT atetal SECKOtlOie occas excacic ccna sosaness weenusompecte sees 98 Lavas 23, 35, 94, 98, 134, 136, 137, 142 Leadville 22, 32, 38, 55, 56, 85, 94, 95, 99, 100, I14, 156-163 Limestone +--+ e00+ 22+ -- 18, 22, 28, 98, 100 Lincoln Mt. cess cece nee eee st wees 20, 17, 153 Lithology s200 -- 20-2 ne eee nnn ee eee ene eee 47 CTLOANHEGS os.0ccnegemaesada ts wansina scene emasaienbeey en elt 108, 109 Locating se eseee ne ccce ccs cneeee-- 14, 172, 173, 200-201 Mammoth . 0.0.6 e0cccnscnnceseen cceasrwpeerssicancw cetacean a 24, 46 ManOW scan cp ace decoy ct cenncbes cedenas Ha eedeSdasee smaeen eons Ig Manganese +--+ 22 eee ee rrr een ee .-+-59, 160 Mesozoic, Meaning of + 34 Metasomatic Replacement 74, 97; 162, 165 MWilee oo cies tewncew sed aks ORena Ee dded Sateen cebesneee eae ee 51 Microscopy of Minerals. + 133-135 Mineralogy +--+-- Likinceminaa ewes wie waaiare SER 59 MineralSac: scucccee go csccueecesseeis 50, 51, 59, 62, 63, 64-67, 161 Mineral Waters... 0.0. s000 2-5. e nce n ned cost eemcsce -.-69, 70 Mining Laws +--+ --00--- 2-2 neon eee e nee eeee 200-201 Mosquito Range +--+ secre eee - 157 Nebular Theory dis Sag RACE CRIME OS Neate ERS eS 25 NGPGCte. . ou... 5 se oe new en ee des ceecees II, 95, 105, 106, III, 164 ODSIMaN ac cae cect os Loewen eck eee cbse sceege nue ce steewese 58 Openings in Rocks 68-71 Ore Chimneys 002 -- +22 eee ee ener ee eree 164 Ore' Deposits weeic -son-sence cece sees 67, 74, 75, 83, 94, 159, 160 OUPCHOD icon ins Sako i senna eay ment aa be eee dane bed net 88 OUthtss soos ok cee ewcccd oes. wad cece rec eeeees coe renetaaeees 9 Paleozoic, Meaning of +eer- 32 Paleontology —. 26... se 0enn caw cecnnesies Ske tnb ae eK tear Oe ee 36, 39 PARMING oo osce. cnscccec as wc csr eet ne een eeceeene: 12, 13, 14 Pay Streak SRR ee ee rr ry rs 181 PHONO Gc shewe se cease csc ctiee dace d deme cee we tng eiee weneigien 137, 142 PIACOPE a... 5 chsas eee ava eae ates' TI, 13, 35, 30, 104-117, I14, 201 POCKEtS asco ad cesce Waien setacbacactcsctaseeeubeesanese gI Poly basite 20. cece cence ce ne eee eens ent eeeee eet ewen cso 63 Porphyty 2--ee-ese- , 50, 55, 56, 94, 134, 154, 168 PresCambrlat i. ccucvacucceccctacdes Gecrenmrcensesesewes Bers PYPHOG onc ees veccn vean eed scence sewsseciondseredoes 62, 88, 181

Quartz 022. 226 oe ee ence ee ee tee ewe ew em enc be er cewencne

Page

Quartz Porphyry... scccccccencenes dimen o 55, 56, 57, 121, 154 Quartzite i nae eeeewinyndet es 4ueee 18, 21, 22, 28, 53, 163 CHIACOINELY: sane os 2. cccenamocesgcececene errr eyes 23, 35 RGGSAGTSUIDANGERC: occeadccsddades cceeeh.senetebueosk ous 36 ReEdi@ fis Minesis- Wc acon se oa code edenccmaeseace 28, 62, 163, 164 RUVOING: cochcanewiesatsabuwed onions ee. le aweemes 23, 35. 57, 94, I51 Richness with Depth whabawoesetes QI, 92, 148, 177 ROCKSi peso ude cased wccneleeameeian sa cacceneetoew ene

PUNY, DIVO. c cedoeccpebecepedich ene deenaeeen cele cupeerweee 61, 64 Salting. Minegesss, cu o5s.cc catesxeeenSoncedmesareees 178, 185-192 DAMPNYE DIINOE> cancaeceedgiacins bosses eubban Soce-eneenenunn 179, 188 SHUUMONUST ay cna sacavass auch eeddvandy~upascdaspadoues 18, 21, 98 San Juan Mining Region 35, 78, 87-S9, 95, 97, 99, +95 124-127, 176, 177 SONIStSe cc ccsackwarnse Sacuiuydocewae ened with aes Sake e ae 53 Sedimentary RUS eAs foc ascwuteceus geeks wend nani 48, 151 BODOG tide we seanuks Adena ee eakwveee epebcatoonsarg eaten 54 Sharpening Tools Ritte Ce RUSRE Sem EARS eal aina Pe aeael ee mgaE 196 SidGhite 1rondo as wo ac. cuewicwin ecncc.cte Diecut He ee ciccimaceele bee oe 60 4 SUMMA te Bosse se Sot ocaees eos cleceeeetoates' 21, 28, 41, 48 ; SilVer Glia MiIneS cc Socata cues neuen Gaeacseeciereweewaece 35, 127 q Silver Reef Sandstone 33, 82 SoltatariccA Chon. sc ccausousncswwsecoeemeceeuoueese 139, 140 BOMMMONE cas veds cewek cases 67-73, 97, 99, 100, T04, 125, 138, 169 South Park Mining ROEQON GS dccineeesccisncns 20, 49, 81, 116, 151-156 DUBAI DONG CONNEC. bein wae cbaccwaateneareeksaeh" Ka So ueehek 140 UO TT 0 Se raga ue dwn bcuened bee Ve enews Kdasaaeeaeae eR sees 63 DMIKG oneal be sec cicee ails Bote anak asics eet were 85, IOI-102

PULOMUON VOLCANO. occ csccwicc cde set du catesieneeeabupewene sun 128 DU RO OUER waders Wavetssebaadaew hae' cs wade 95, 147, 148, 174 UDIAOR WISE a oh cs bw akoa dk caitwk ved ensheechadaemerrkwewe 75,79

aa RELATE OMEN PERC ES A os Ee Sonus eelee Cee ROA SESE Ea ae ee o83

ee ee en fe ee 2 oe

eawentg MIO Gl i iateiee as." wee oe kee S Re Meee ub annoy MPORUGT os css Sie es Sve RR Mus hedge a becca yeneus 23, 34, 97, 124 iy 5 RL 6) Se a WEE Mice a Secu ees SPRAGUE? LAV Msn cincs voce Gbede wkend ne eee edes COLDER DeAaR aes TREMORS cewek.' cecudnie sds ess dew bann eu nadtan omananaea 22, 32, 44 UTI NGIS wate dé o.n holt So Sowicin shah ats, arate Suan da oe cue wae te DE Bae

-- 34, 35, 93, 127, 128, 131, 135, 141, a 153, 155 Stckdahetdnabae sa ckebekear sonGavekanekat eeaeec 86, a

ee ee ee eos

List Of Authors, 207

List Of Authors And Works Referred To.

Balch, W. R. ) Mines, Miners and Mining Interests of the United Balch, A. ) States.

Cross, Whitman.—Geology of Cripple Creek.

Dana, J. D.—Geology and Mineralogy.

Emmons, S. F.—Geology and Mining Industry of Leadville. Farish, J. B.—A Typical Boulder County Mine.

Geikie, A.—Hand Book of Field Geology.

Guiterman, F.—Red Cliff Gold Deposits.

Ihlseng, M. C.—Manual of Mining.

Judd, J. W.—Volcanoes.

Kemp, J. F.—Ore Deposits.

ULakes, A..—Geology of Colorado and Western Ore Deposits. Le Conte, J.—Geology.

Lock, A. G.—Gold, its Occurrence and Extraction,

Lock, C. G. W.—Practical Gold Mining.

Penrose, Arthur.—Ore Deposits of Cripple Creek.

Phillips, J. A.—Ore Deposits.

Williams, Albert, Jr.—Mineral Resources of the United States.