GEOLOGICAL SKETCHES OF 'I' UK PRECIOUS METAL DEPOSITS OF THE WESTERN UNITED STATES, BY F. EMMOXS AND G. F. BECKER, WITH NOTES ON LEAD SMELTING AT LEADVILLE. EXTKArT FKOM Till: 'IK NTH CKNSITS OF THE CNITKD STATES, VOL. XIII "STATISTICS AND OK THE 1'KECIors METAI \V A S II I N G T O X : G O V K K N M i: X T P R I N T I N U O F F ICE. 1 8 GEOLOGICAL SKETCHES OF THE PRECIOUS METAL DEPOSITS OF THE WESTERN UNITED STATES, BY S. F: EMMOXS AND GfF.* DECKER, ? WITH NOTES ON LEAD SMELTING AT LEADVILLE. EXTRACT FROM THE TENTH CENSUS OF THE UNITED STATES, VOL. XIII "STATISTICS AND TECHNOLOGY OF THE PRECIOUS META1 \V A S II I N G T O N : GOVERNMENT PRINTING OFFICE. 1885. oft Ubnuy STATISTICS AND TECHNOLOGY OF THE PRECIOUS METALS. CHAPTER I. GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. BY GEORGE F. BKCKER. It is the purpose of this chapter to present such au outline of the geology of each of the states and territories west of the Rocky mountains as will serve to assist those unfamiliar with the country in forming an idea of the character and distribution of its mineral resources, and to convey such rudimentary information concerning the relations which the ore deposits bear to the larger features of the geological structure as is necessary to an intelligent perusal of the statistical chapters. The information available for this purpose is far from ample. The government geological explorations of the last twenty years have done a large amount of extremely valuable work, Bme of which has made a permanent mark on the history of the science; but the territory is so vast that many decades must elapse before even the preliminary explorations are completed. The collections and the data gathered! by the census experts are also very valuable. Few mines, however, can be properly understood without a somewhat extended examination of the surrounding country, for which the experts had no time, and the information is therefore rather fragmentary. The order adopted in sketching the states and territories is not that which would have been chosen had the information been more complete. Washington territory and Oregon are placed after California, because little is known of them directly, while certain inferences maybe legitimately drawn from the analogous territory embraced in the last-named state, and Idaho is described after Nevada and Utah for similar reasons. The regularity of the distribution of ores in the Pacific division and its relations to the singularly uniform- topography long ago drew the attention of writers to the resources of this region. Mr. W. P. Blake (a) first published a note on the subject in 1866, and his statement was accepted and enlarged upon by Mr. King (b) in 1870. The more detailed technical and scientific investigations of later years have greatly increased our knowledge of the distribution and extent of the ores, and it will now scarcely be maintained that there are more than four well defined and continuous ore belts west of the Rocky mountains. Beginning at the east, the first is that at the western foot of the Wahsateh and the southwestern continuation of that range. With the exception of the Leeds (Silver Reef) district, all the important ore deposits of Utah lie in the foot-hills of this range, bearing a very definite relation to the main line of crests. The gold and copper belt of California stands for a long distance in a similar relation to the Sierra Nevada. The quicksilver belt in the California coast ranges is not quite so regular in its occurrence, yet its direction is very nearly parallel to the coast, and it is very persistent, though nowhere broad, for some 300 or 400 miles. The Arizona belt is less known than any of the others, but no one can glance at a map of the territory showing the mining districts without perceiving that these lie in a northwestern and southeastern line diagonally across the country. The mining districts in Nevada are extremely numerous, so niHch so indeed that some grounds could be given for assuming a belt to run in almost any desired direction, but they are scarcely close or regular enough in any one line to compel the observer to regard them as connected. These four distinct belts appear to have an intimate connection with the four great orographical changes which the region west of the Rocky mountains has undergone during its geological history. The last of these was post- Miocene, and resulted in the uplift of the Pacific Coast ranges and the great interior valley of California, with a large part of Oregon and Washington territory. The disturbing force seems to have been most powerful to the north and south of San Francisco, or approximately in the region marked by the quicksilver deposits. A post Cretaceous, upheaval raised the whole western central portion of the continent now occupied by the complex system of the a Annotated catalogue of the principal mineral species hitherto recognized in California, etc. Report to state board of agriculture, p. 26. Exploration of tkt 40(A Parallel, iii, p. 5. 6 PRECIOUS METALS. Bocky mountains. The Wahsatch forms the western edge of this uplift, ;mtl the dislocation took place on an old fault coincident with the present western foot of that range. Here also lie the numerous mines of Utah. The Sierra Nevada and the ranges of the Great Basin were raised by a post-Jurassic uplift. The line of most intense disturbance coincided with the Sierra, and the greatest dislocation occurred along its western foot, in the gold belt, though it also extended to the south of that wonderful series of deposits. The earliest disturbance in the far west was that which raised the Palaeozoic strata of eastern Nevada, western Utah, and a portion of Arizona above the surface of the ancient sea. The western limit of this Palaeozoic area has been traced in detail across the belt surveyed by the exploration of the fortieth parallel, and i^that latitude it trends nearly north and south in longitude 117 30'. To the south the limit has been fixed at aw>nsiderable number of points, though it has not been followed in detail. South of Austin the course of the western edge of the Palaeozoic is somewhat west of south, and it enters California a little north of Owen's lake. In this region it is deflected toward the southeast, crosses the Colorado river in Virgin canon, passes by Prescott, and on through Arizona to the neighborhood of Tombstone. The main Arizona belt of deposits has the same trend as the border of the Palaeozoic, and nearly coincides with it in position. In short, though the relation still requires much investigation, the Arizona mineral belt appears to stand in nearly the same relation to the western edge of the post-Carboniferous upheaval as do the belts of Utah and California to the other uplifts. That these relations exist as a matter of fact is beyond question, though it is possible that they may be accidental. In any case, however, the uplifts, as such, are not to be regarded as the cause of the formation of the mineral belts ; these must rather be due to the fissuring of the rocks and the dislocations attending the orographical changes. There is evidence that the post-Carboniferous uplift in the state of Nevada and in southeastern California was comparatively gentle, and that it was not attended by any considerable crumpling of the strata. This would account for the fact that the number of ore deposits 'at its edge in these states is not very large. Nevertheless, the lead deposits of Battle Mountain, the Austin mines, the Candelaria district (which includes the famous Northern Belle mine), Panamint, and Cerro Gordo all occur at or close to the western edge of the Palaeozoic. Taken in connection with the geological similarity of their position to that of the Arizona mines, these deposits may perhaps fairly be regarded as the rudiments of a belt. In Arizona the area in which the contact occurs has been too little investigated to allow of any statement as to the violence of the uplift, but, all things considered, it would be remarkable if it should not ultimately prove to have been attended by much disturbance. This theory of a relation between the ore-belts and the lines of uplift is, of course, not to be understood as equivalent to the assertion that the deposits are to be found only along a single line representing the actual main fissure of the uplift. One is apt to think of the dislocation attending an orographical change as confined to a single vertical or highly inclined surface, but every geologist is aware that this is not an exact view. Simple fissures in the earth's crust are very rare, and parallel sets of fissures, with cross fractures and stringers into the surrounding country, are the rule even in the case of insignificant cracks. In disturbances such as those of the great uplifts a considerable belt of country is almost necessarily crushed and torn, and innumerable rents and cracks standing in most complex relations to one another penetrate the rocks in many directions. The breadth of such a zone must usually be measured in miles. It may be that some of the ore deposits of the Pacific division are independent of volcanic action, but the association of eruptive rocks with ores is a rule with comparatively few apparent exceptions, and in many cases the agency of solfataric action () is manifest. This has long been recognized by observers. That there are relations between the rocks inclosing ore deposits and the character of the ores has been known to miners for centuries, but the study of the nature of this dependence is comparatively new. It is far too complex a subject to be discussed in this chapter, but it may at least be stated that the census collections and data appear to confirm, emphatically, the existence of such relations. Lead ores are almost invariably accompanied by limestone, and veins in granite present only a very small number of associations of minerals, which are possibly reducible to a single one. Deposits in metamorphic rocks, too, though more varied than the others, appear to represent but a few types. It was not practicable, however, for the experts to make such minute examinations of the mines as would have been necessary to furnish material for a conclusive investigation of this subject. With some hesitation most of the determinations of the ore and gaugue minerals, the country rocks, and the kind of deposit, are introduced county by county. There can be no doubt that the list of ore minerals is often imperfect. The determination of the wall rocks is subject to some uncertainty without a thorough examination in the field aa well as in the study, and the nature of a deposit is in many cases not to be decided by a single visit. It is probable, however, that the determinations of rocks and minerals are, nearly always correct as far as they go, and in the, cases in which the character of the ore deposits was not clear as much may generally be inferred from the statement regarding them. The tables, therefore, contain much information of value, and many suggestions to such geologists and miners as are careful to remember that they are not exhaustive statements. Except in a few cases, in which I happened to have visited the localities, the determination of the character of the deposits rests on the authority of the experts. The determinations of rocks and minerals inclosed in parenthesis are also due to the experts, a AH originally employed, the term solfataric action denoted only the effect of gaseous emanations from volcanic vents. In use, however, it has gradually coine to include the action of heated waters charged with these giwes or holding them in solution, and is BO employed in this chanter. GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 7 while the remainder I have made from the specimens collected by my assistants. The difficulties met with in making these determinations were considerable, for rocks near ore deposits are usually, much altered, and the ore minerals need much closer attention than in ordinary specimens of merely mineralogical interest. A few minute particles of such minerals in a hand specimen often make the difference between waste rock and rich ore and the inspection of the samples needed to be correspondingly searching. Maps of the states and territories of the Pacific division accompany the sketches. These are necessarily on a small scale, but present the leading features sufficiently well to assist the reader in following the descriptions. On them are entered signs indicating the distribution of gold, silver, and quicksilver. These are not designed to represent every spot where precious metals have been detected, but to indicate at a glance their general distribution. GEOLOGICAL SKETCH OF CALIFORNIA. The mineral resources of California are extremely varied, but are also of very unequal importance. Its gold production is an essential factor in determining the relations of the mediums of exchange throughout the world, its total value since 1849 exceeding $1,200,000,000. Its quicksilver production, also, though of far less value, exceeds that of any other country. The total known product of California from 1850 to the close of 1880 was a trifle less than 91,000,000 pounds, of an average value of 71 cents, and has yielded above $65,000,000. It is important as an adjunct to the precious-metal industries no less than as an independent source of profit. The silver product yields above a million per year ; and the coal-fields, though not of the best, furnish a large part of the supply necessary for home consumption. Asphalt and petroleum are obtained in small quantities, and some sulphur and borax are extracted, while lead is reduced only as an incident of the silver industries, and copper and iron, though their ores are plentiful, are worked on a small scale only. Tin, chromic iron, black oxide of manganese, and other useful minerals also occur in the state, but as yet contribute little to its commercial prosperity. The great industrial importance of the gold production of California has drawn the attention of many geologists and engineers to the geology of the state, and the literature on the subject is comparatively extensive. The Pacific railroad survey, Mr. J. A. Phillips' work on gold and silver, the reports of the mining commissioners, the proceedings of the California Academy of Sciences, and the scientific journals of America and Europe, all contain contributions to the subject; but the chief source of authority is the volumes of the state geological survey of California, conducted under the charge of Professor J. D. Whitney, who had the assistance of Messrs. Clarence King, W. H. Brewer, W. M. Gabb, William Ash burner, W. H. Pettee, and others. Unfortunately, the legislature ceased to appropriate funds for the survey in 1874 before a single geological map had been issued. Professor Whitney, however, has continued to work up the material collected, and has issued a number of volumes during the last eight years. The census reports and collections also furnish some information of value from a geological point of view, but the following sketch owes most to the data collected by Professor Whitney and his assistants or recorded in the volumes published under his supervision. The interior of California forms a long, oval valley. Its greater diameter is parallel to the coast, and extends from th neighborhood of Fort Tejon to Mount Shasta, a distance of 450 miles, while the average width is about 40 miles. This valley is surrounded by mountains, except at a single point, where San Francisco, San Pablo, and Suisun bays afford an outlet for the drainage gathered by the Sacramento river from the north and the San Joaquin from the south. Though the mountain ranges inclosing this basin unite at its extremities, the Great Valley is not a mere undisturbed area between different ranges of a complex chain ; on the contrary, the Sierra Nevada to the east and the Coast ranges to the west represent upheavals of different characters and widely distant eras. The Sierm Nevada is a single range forming the western rampart of the elevated plateau of the Great Basin, and was raised in post- Jurassic times. The Coast ranges consist largely of detritus from the Sierra; they were uplifted for the most part at the end of the Miocene, and constitute a mountainous belt of country to which even the name of chain can scarcely be applied. No term answering to the Coast ranges was used by the Spanish settlers of the country, but they gave special names to a considerable number of small ranges within the Coast belt, and these are still in use. The elevation of the Coast ranges is greatly inferior to that of the Sierra, a number of peaks of the latter exceeding 14,000 feet, while none of the culminating points of the Coast ranges appear to rise more than 6,000 feet above sea level. Both the Sierra Nevada and the Coast ranges are greatly metamorphosed and contain extensive deposits of useful minerals, and the alteration of the strata and the deposition of ore are probably in each case related phenomena ; but the metamorphosis and ore-deposition of the Coast ranges occurred long after the cessation of similar activity in the Sierra, and led to widely different results. The more remarkable deposits of the Coast ranges are cinnabar, chromic iron, coal, asphalt, and mineral oil, Awhile gold and copper are characteristic of the western slope of the Sierra, lead and more or less auriferous silver occurring very extensively on the eastern slope, of which only a portion lies within the limits of the state. The backbone of the Sierra is granitic, the higher summits and a large part of the western slope of the range being of this rock, except in the northern portion of the state, where it has been covered by basaltic and 8 PRECIOUS METALS. andesitic lavas. The granite penetrates some of the accompanying strata in dikes, and Professor Whitney regaich it as beyond question of eruptive origin, while some other geologists see iu it only highly metainorphosed.seditnentary material reduced to a plastic state in situ. Except at the northern end of the Great Valley, near Mount Shasta, and near Owen's lake, no Palaeozoic strata have been identified. lu the Gray mountains, Shasta county, a limited area of Carboniferous limestone occurs, amply identified by fossils. A small amount of limestone with the same external characteristics occurs farther south, and Professor Whitney regards it as not improbably of the same age. From a mining point of view, however, it is insignificant, carrying little gold. The principal strata on the west flank of the Sierra are Jurassic and Triassic, occurring chiefly and characteristically as slates and shales. They are highly metamorphic, contain few fossils, and have been profoundly disturbed, showing that the range was uplifted since their deposition. These are the main gold-bearing rocks, and will be more particularly described further on. Near the foot of the range are areas of Cretaceous and Tertiary beds, chiefly marine, nearly horizontal, and resting unconfoi-m- ably on the upturned auriferous slates. Above the Mesozoic slates lie fresh-water auriferous gravels, mainly of Tertiary age, and these toward the north are in part covered by flows of Tertiary and post-Tertiary lavas. Inyo and Mono counties lie to the east of the Sierra. The metamorphic slates and limestones of this region are for the most part Triassic, though the Jurassic is probably also represented, and are covered to a great extent by volcanic rocks. Mr. Gilbert has shown that the eastern edge of Inyo county reaches the Paleozoic area. The Jura-Trias strata extend to the east of the Sierra abont as far as longitude 117 30'. They rest directly upon Archaean schists and granite, and the long interval of time which they represent seems to have been extremely quiet, for no non-conformity has been detected in the series. At the close of the Jurassic, however, the whole area from the western foot of tbe Sierra to the middle of the state of Nevada was raised above the ocean and compressed from west to east, resulting in the formation of a number of parallel ranges, of which the most westerly were the Sierra Nevada and the Blue Mountain range of Oregon. Ore deposits occur on the eastern as well as on the western flank of the Sierra, but their character and mode of occurrence differ from those prevailing in the gold belt. The Coast ranges, or the western mountainous belt between Mount Shasta and fort Tejou, are for the most part composed of more or less altered rocks of Cretaceous and Tertiary age. The geologists and the paleontologists of the state survey divided the Cretaceous into lower and upper, and, while recognizing the later divisions of the Tertiary, failed to find anything certainly corresponding to Eocene. Of late, however, it has been shown that the fossils of what had been considered as the Upper Cretaceous exhibit strongly marked Tertiary affinities, and it seems by no means impossible that the beds in question, which are sometimes called the Tejon group, and include the Monte Diablo coal-fields, really represent the Eocene. Considering that differences of climate must always have existed, whether more or less marked than those of the present time, it is not strange that doubtful cases like those of the Tejon group, the Laramie beds, and the Australian coal-bearing rocks occur, but rather that it is so often possible to determine the correspondence of strata in widely separated areas. Though the Coast ranges here and there show granitic rocks, granite is of only local importance, and does not appear to form the central mass, as is the case with the Sierra. The body of these ranges is made up of crumpled and fractured strata, indicating, according to Professor Whitney, sharp and sudden elevations and depressions, extending through the Pliocene epoch. To the southward the prevailing rocks are Tertiary, but north of the bay of San Francisco these almost disappear, the Cretaceous becoming predominant. Volcanic rocks are not widely spread, most of the known occurrences being found between San Francisco and Clear lake. It appears, therefore, that the elevation of the coast as a whole was comparatively recent. While the quartz veins were forming, and while the gravels were accumulating ou the west flank of the Sierra, the region of the Coast ranges and the Great Valley were wholly or partly under a gulf or sea, shallow in parts and surrounding more or less extensive islands. The existence of this shallow sea must have had an important influence OH the climate of the Sierra, for, supposing the evaporation to have been the same, nearly the whole amount of moisture now distributed through the Coast ranges and the interior of California would have fallen on the Sierra in addition to its present rainfall. But evaporation is considerably more rapid from shallow seas than from deep ones, and the rainfall on the Sierra must consequently have been enormous. The chief uplift of the Coast ranges took place at the close of the Miocene, and the great metamorphism and ore deposition are probably for the most part referable to the same period, though it is likely that the still later volcanic eruptions induced a portion of them. The Pliocene or post-Pliocene disturbances were comparatively gentle, but Professor Whitney regards the break at the Golden Gate, the prevalence of volcanic rocks from that point north to Clear lake, and the disturbances of the Pliocene south of San Francisco bay, as connected phenomena. The region south of fort Tejon has been much less investigated than the central portion cf the state. It appears to possess some extremely interesting geological features, but also to present unusual difficulties. The San Gabriel range north of Los Angeles has a granitic axis, and it is possible to trace this granite ridge uninterruptedly through Los Angeles, San Bernardino, and San Diego counties into Lower California, and along the peninsula to within a few miles of tbe old mission of Santa Gertrudis. (a) The sedimentary rocks accompanying this granite ridge are for the most part highly metamorphosed, and are frequently penetrated by dikes of granite. They are nevertheless considered by both Professor Whitney and Mr. Gabb as of Cretaceous and Tertiary age, and the uplift is referred, like that .of the Coast ranges proper, to the close of the Miocene. a Geological Survey f California, ii, 137. GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 9 Besides the bitumen springs of Ventura and Los Angeles counties, there are gold mines in this southern California range, but few details have been published as to their occurrence, and their geological relations are still to be studied. The character of the rocks of the Coast range shows that the Cretaceous and Tertiary sea near the present coast was shallow, but there is evidence that the Great Valley represents a former depression of immense depth. This, .however, would not prevent the gulf at the foot of the Tertiary Sierra from being as warm, for example, as the Gulf of Mexico, for the temperature of the water of a land-locked basin depends on the depth of the inlet to it, and if this is small the water of the basin will be warm. In Russia and Australia the Silurian is the gold-bearing formation, and Sir Roderick Murchisou enunciated the somewhat rash generalization that gold was to be looked for only in the Palaeozoic. In California it is amply proved by rare, but characteristic fossils that the gold-bearing sedimentary rocks are Mesozoic. Generalizations similar to Murchison's have been attempted with reference to ores of other metals, but the simple fact seems to be that eruptive activity or inetamorphisin is usually a concomitant of the concentration of ores in veins and other allied deposits, and that the older the rocks the greater the general probability that they will have been subjected to action of this description. In the search for coal the fact that the important deposits of the best character are confined to one formation has been of great economical value. The geological indications accompanying the occurrence of veins are to be sought, not in the age of the rocks, but in evidences of disturbance and of certain kinds of decomposition of the surrounding country. The decomposition or alteration of rocks in the neighborhood of ore deposits has been but little studied by geologists until lately, for very sufficient reasons; but of the fact of a connectiou between it and the deposition of ore California affords excellent examples. The "bed-rock" or auriferous slates of the gold belt is characteristically altered, and the metamorphic stratum in which cinnabar occurs art- at once recognized by those familiar with them as "quicksilver rock". The belt of metamorphic rocks which incloses the greater part of the gold-quartz veins of California is insignificant in width and of little industrial importance south of the southern boundary of Mariposa county. To the north of that line, however, it suddenly widens. Passing northward, the breadth of the belt is stated at about 25 miles in Tuolumne county, 24 miles in Calaveras, 12 in Amador, and 30 in El Dorado. In Placer it is not well exposed, being covered by gravel and volcanic rocks. North of Placer county the metamorphics occupy most of the western slope of the range for a considerable distance, with occasional irregularly distributed patches of granite, but in Uutte county the edge of the great lava fields, which occupy much of the surface of northeastern California, are encountered, and cut off the central mining region. The same gold-bearing series seems to reappear in the north- western counties, but its character and relations are less well understood, and its industrial importance is smaller than in central California. As illustrative of the structure of the gold belt, Professor Whitney describes in some detail the important portion lying between the Merced and the Stanislaus rivers. Starting from the west, or at the bottom of tb Sierra, the first rock encountered is horizontally stratified and undisturbed Tertiary sandstone. To this succeeds the belt of Mesozoic metamorphics in nearly vertical strata. The lower edge is composed of talcose and chloritic slates, weathering irregularly, and locally known as "grave-stone" slates. Next comes a wide belt of a dark-grayish green, somewhat porphyritic, material, which shows a sheeted structure, though not the fine lamination of clay slates. This was known to the state survey as i( porphyritic green slate", but Professor Whitney and Mr. Wadsworth are inclined to regard it as a metamorphosed diabasitic tufa. This belt incloses another of argillaceous slate, carrying Jurassic fossils, with which is associated the "mother lode", or the "great quartz vein". Accompanying the argillaceous slate and the mother lodeisa band of serpentine, (a) In the southern portion of this section the seqjeutine is confined to the northeast side of the argillaceous slate, but near the Stanislaus river it widens out, occurring in irregular patches and on both sides of the slates. The strike of the metamorphosed rocks is, as a whole, parallel to the trend of the Sierra, but there are many sharp deflections. The dip of the slates in the southern and central portion of the gold belt is nearly vertical, and usually to the northeast; but in the northern portion, where the belt widens out, the dip becomes irregular, and over wide areas is to the west, becoming natter as the distance from the crest of the range increases. Though not confined to the argillaceous slates, or even to the metamorphic strata, the gold-quartz veins of California are more frequent and richer in the argillaceous slates than elsewhere, many fine veins beside the "mother lode" occurring in it. The veins are usually parallel to the stratification, as the following quotation shows :(b) A very heavy quartz vein passes a little south ef Big Oak Flat, Tuoluume county, cutting the strata of slate in which it is contained at a small angle, the lines of bedding of the wall-rock appearing to run nearly northwest and southeast, while the vein of quartz has a strike of N. 30 W.; it dips to the tast at tin angle of 30, the slates themselves standing nearly vertical. This is, perhaps the most marked instance hitherto observed in the state of a heavy quartz vein differing essentially both in dip and strike from the inclosing rucks. a The origin of serpentine is a disputed point. If it is a fact, as eminent mineralogists have maintained, that it occurs as an alteration of hornblende and pyroxene as well as of olivine, there, appears t be no difficulty in accounting for its presence in metamorphic rocks. Chlorite and serpentine, however, are ccusioually confounded. b Geological Surrey of California : Geology, vol I, p. 237. 10 PRECIOUS METALS. The most remarkable primary metalliferous deposit of California is the mother lode already referred to. Many of tho great mines of the state are upon it, and others are in its immediate vicinity on veins which most likely have an intimate structural connection with it. It extends from a point a few miles southeast of the Merced river, iu Mariposa county, to near the center of Amador, a distance of about 80 miles. Though the croppings are in places hidden by overlying rock or detritus, they are visible for a great portion of the distance at such frequent intervals that the identity of the lode is not doubtful. It is more than probable that it extends to the north of the point, indicated, but it cannot be traced with absolute certainty. This powerful lode (a) is made up of irregularly parallel plates of white compact quartz aud crystalline dolomite or uiagnesite (6) more or less mixed with green talc; and these plates, which somewhat resemble the "combs" of ordinary lodes, are either in contact or separated from each other by intercalated layers of talcose slate. The quartz is chiefly developed in the central portion of tho vein; and, from its color and resistance to decomposition, it gives rise to a very conspicuous outcrop, forming the crest of the hills, so that it can be readily seen from a distance of several miles. The dolotnitic or magnesitic portion decomposes somewhat readily, and it becomes a kind of "gossan "or cellular, ferruginous mass, of a dark-brown color, often traversed in every direction by seams of white quartz. The quartz is the auriferous portion of the lode, although it is far from being uniformly impregnated with gold. Most of the mines which have been worked between the Merced and the Stanislaus are on the northeast side of the great quartz vein, either in contact with it or in some parallel band of quartz subordinate to or at a little distance from it. The talcose-slate bands in the vein are often themselves more or less auriferous. Professor Whitney does not regard it as by any means proved to be a fissure vein, or even an exclusively segregated one; on the contrary, it seems to him most likely the result of metamorphic action on a belt of rock of peculiar composition, and perhaps originally largely dolomitic in character. Besides the quartz veins in the metamorphics of California, there are also many in the granites of the same region. Though of less importance than those in the sedimentary rocks, many of them have been worked with profit, but no careful comparison has been instituted between the two classes of veins. In some instances at least, and when near the slates, the veins in the granite are parallel to the stratification of the metamorphic rocks, and are also essentially gold veins. It is probable, however, that on closer investigation they will be found to present characteristic differences. Gold never occurs in nature unassociated with silver, and silver, it is said, is never wholly free from gold ; but there seems, nevertheless, to be a natural distinction between gold veins and silver veins. In Nevada, Arizona, and throughout Mexico gold usually occurs only in minute particles entangled in sulpho-salts of silver and other metals, except near the surface, where atmospheric action has decomposed the original matrix. Though the value of the gold in such cases sometimes equals or exceeds that of the accompanying silver, the latter usually greatly surpasses it iu weight. In the gold belt of California, on the other hand, the gold occurs in great part as flakes or even as masses, often not immediately iu contact with sulphides, and carrying in alloy only 0.100 or 0.200 of metallic silver. As a rule, the gold does not assume a crystalline form in the California mines, but more or less perfect octohedral forms have been found at Spanish Dry Diggings and at Byrd's valley. Cubical crystals have not until lately been observed, and Professor Whitney notes that he has neither seen nor heard of any in the state, (c) Sulphides always accompany the gold iu the veins, though these minerals are not always found in contact with the larger particles of the metal. So general is the association, however, that when, as is often the case even with rich quartz, the gold is not visible to the naked eye, miners judge of the value of the ore by the quantity of sulphnrets. Quartz with plenty of sulphurets and no visible gold often occurs in large bodies, and is apt to pay better in the long run than ore with very coarse gold, or " specimen quartz", as it is called by the miners. The minerals embraced under the term "sulphurets" are considerable in number, but the most common are pyrite, mispickel, ziucblende, and galena. Though seldom containing the greater part of the gold, it is rarely that the sulphurets do not include a portion of the metal in such a way that it cannot be extracted by amalgamation. Concentration of the sulphurets, followed by chloridatiou, is then the readiest means of extraction. There is an occurrence of cinnabar in gold quartz veins inclosed in slate in Calaveras and one in Mariposa. The distribution of gold in the veins is usually very irregular, and while on some veins it will pay to extract the ore from wall to wall, in most cases certain belts or chimneys of rock only are remunerative. Had the veins been deposited in the slates before they were raised into their present position in post- Jurassic times, they must have been much faulted and broken. This is not the case, nor is it probable that veins could have formed in undisturbed strata. On the other hand, there can be no doubt that the auriferous gravels have been formed at the expense of eroded croppings of the quartz veins ; and the veins, or most of them, must therefore have been deposited before the gravels. These, according to Professor Whitney, were accumulated during the whole of the Tertiary period, while Cretaceous gravels appear to be entirely absent. The range was above water during a Professor Whitney: Auriferous Gravels, p. 46. It In the only specimen which has thus far been chemically examined the supposed dolomitic portion proves to be an intimate mixture of quartz and magnesite. o In December, 1882, however, Mr. James Terry purchased a specimen of gold from Louis Abraham, Kearney street, San Francisco, which is said to have come from Eldorado county, between Plumas and Placerville, which shows a number of fine cubical crystals witk full faces and sharp edges. The same specimen also shows well-developed dodecahedrons, trapezohedrons combined with the cube and octohedron, a cube the corners of which are truncated by a trapezohedron, and possibly other combinations. GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 11 the Cretaceous, jiud such fresh- water deposits as accumulated ou its west slope seem to have beeu swept away during the succeeding period. The natural inference would seem to be that the formation of the veins occurred between the end of the Jurassic aud the beginning of the Tertiary, and that it was intimately connected with the upheaval of the Sierra and the metamorphisin of the strata of preceding epochs. Substantially coincident with the area of gold veins is that of the auriferous gravels of California. In the gold bearing regions of all countries secondary deposits of the metal, associated with gravel or sand, have played ;i large part, because the gold may be separated from such loose material at a low cost. In California, however, the gravels have proved particularly important because of the invention and development there of the peculiar system of hydraulic mining, which consists in washing the gravels into sluices provided with quicksilver by the aid of powerful jets of water. The great importance of this system is due to the fact that it is among the least costly methods of handling material, if it is not the very cheapest known. It costs under favorable circumstances but five cents per cubic yard, or, say, three cents per ton, and sometimes even less. It thus renders deposits of gravel valuable which under most conditions would be absolutely worthless. Several conditions, however, are necessary to the successful prosecution of hydraulic mining, among which the most important are a deep gravel bank, abundance of water with a great head, and some available valley at a lower level than the bank, into which the gravel from which the gold has been extracted may be washed. The topographical and climatic conditions in the Sierra are peculiarly favorable for this process, while in Australia, where gravel is abundant, circumstances rarely permit the application of this method of extraction. The gravel consists of bowlders and pebbles of various rocks, with silt, clay, and volcanic ash. The gold occurs as nuggets and fine particles, free or nearly free from rock, but also as fragments of gold quartz, and is accompanied by a variety of other heavy substances, as magnetite, garnet, and zircon; rarely and locally also by cinnabar, platinum and iridosmine, diamonds, native copper, and other substauces of high specific gravity. One of the striking features of most deep gravel banks is the so-called "blue lead". This name is applied to the lower portions of banks, which are generally somewhat closely compacted and possess the color of the blue clays occurring all over the world. Although the " blue lead" has led to wholly untenable theories as to the character of the gravel deposits, its nature is very readily accounted for. Loose materials n*>ar the earth's surface are every where impregnated with a small amount of organic matter carried down from the surface by water and filtered from it by the porous strata. This organic matter, in the absence of free oxygen, exercises a slow but inevitable reducing action ou ferric oxide and on some ferric compounds, and gives the soil the bluish color characteristic of the presence of iron in the ferrous state. Close to the surface, however, oxygen, either gaseous or in aqueous solution, more than counterbalances the reducing action of the organic matter, and above a certain line the gravel is consequently reddened by ferric oxide. In shallow deposits the gravel is usually reddened to the bottom, but of course this does not aecessarily imply that such gravels have a different origin from those of a bluish tint. To a very large extent the deep gravels are covered by a capping of volcanic material, sometimes as solid black basalt, and sometimes as loose volcanic " ash"; and while some banks are not thus covered, these are rarely at any great distance from volcanic capping. The volcanic material has protected the gravels in many cases from erosion, but there is also a connection in their deposition. The gravels occur in ancient river beds, which formed the natural channels for the flow of lava as well as of water. Volcanic eruptions occurred during the period of the gravel formation, as well as at its close, and sheets of ash or even of solid lava are found in the banks as well as upon them. When the lava cap is thick and solid the gravels can only be mined by drifting, and are not workable by the, hydraulic process. Besides the deep gravels, which date from a period prior to the volcanic eruptions, there are many accumulations of recent origin. The bars of the present river system have yielded great quantities of gold, and there are many shallow placer deposits which are no doubt due to the modern erosion of quartz croppings, while others are a consequence of the erosion of older gravels. The modern gravels, however, are trifling in quantity as compared with the older deposits. Some of the shallow placers are no doubt mere remnants of deeper Tertiary gravels which have not beeu wholly carried away by the erosion of the present epoch. The bed-rock of the gravel deposits varies in character, being either limestone, granite, or metamorphic slate; but the last is the rule, and few important deposits occur far from the slate bed-rock, which, as has been explained, is the main, though not the exclusive, habitat of the gold veins. In nearly all cases the gravel rests in local depressions, early recognized by the California miners as the beds of former streams. Many of the gravels, it is true, are high above the present drainage system, and even form the tops of hills; but this is due to the erosion of the present stream-beds, which have been cut down to a great depth since the gravel period. The bed-rock is usually rough, consisting of nearly vertical slates, and the natural crevices, or " riffles", large and small, thus formed often contain extremely rich gravel. As might naturally be supposed, the greater part of the gold is generally found near the bed-rock, for as gold is about seven times as heavy as ordinary rock every disturbance of a gravel bar in a stream tends to shift the gold to a lower level. Sometimes, however, rich gravel is again deposited over a comparatively firm stratum in the gravel, and occasionally gold is quite uniformly disseminated through a whole bank. 12 PRECIOUS METALS. An idea has been current in the mining region that by some process masses of gold in the gravel have increased in size. For this there is absolutely no valid evidence. The rounded masses of gold found could not have been deposited from solution in that form or with such a surface. They have been beaten and worn into shape, much as the accompanying pebbles have been formed, the only difference being due to the fact that gold is malleable. Professor Whitney believes it probable that the higher croppings of the gold veins were richer and contained larger masses of gold than the lower portions of the veins still in place, and if there was any difference at all it was probably of that character. As Professor Newberry (a) points out, however, the gravels represent vastly more vein-quartz than has been extracted by deep mining, and the proportion of large masses of gold met with in the veins probably bears as great a ratio to the total weight of quartz extracted, as do the nuggets in the gravels to the quartz from which their metallic contents were derived. The investigations of the state survey have shown that the deep gravels were deposited by rivers which headed in the high Sierra and ran in a westerly direction, emptying into the sea, which, in Tertiary time, occupied the great valley of California. Although all the details of the former river system cannot now be traced out, the courses and relations of the channels developed by hydraulic mining seem to establish this point beyond a question. There were two great rivers in the Pliocene epoch, one corresponding to the American and the other to the Yuba; but the Bear river of that time probably emptied into the American at a considerable height above the valley. The gravels cannot possibly have accumulated under the present conditions of precipitation. A far greater erosive power than that exhibited by the California streams of to-day must have been exerted at the time in question, as no one can doubt who has ever visited the gold belt. For a long time past the present rivers have merely been deepening their narrow courses, and when freshets occur they merely serve to sweep the canons clear of debris, but cannot alter the course of the stream. The width of the old channels, as well as the character of the deposits, shows that the old rivers were tumultuous streams of great volume, which frequently burst their bounds and formed new beds. The evidence of enormous erosive power during the deposition of the gravel has been so apparent to all observers that some of them have called in the action of great glaciers to account for the occurrence of the deposits. According to Professor Whitney this is incorrect ; indeed, lie holds that the former glaciers of the Sierra did not come, into existence until after the greater part of the gravels occupied their present position. The bed-rock which the gravels cover, and which they have protected uot only from erosion but even from atmospheric action, shows no traces of glacial polishing and scratching. This is in marked contrast to the higher regions of the range, where the glacial markings are almost as fresh as in the Alps. Nor are occurrences frequent which can possibly be confounded with moraines, while the fossils found indicate, according to Mr. Lesquerenx, a climate a few degrees warmer than that of the present time. Professor Whitney believes the great precipitation necessary to account for the large rivers of the Tertiary in California to have been mainly due to the prevalence of higher temperatures at that period and to the accompany i:,g increased evaporation from the surface of tlie ocean. It is at least conceivable that the climate should have been something like that of the Khassia hills, upon parts of which the hot winds from the bay of Bengal deposit some 500 inches of rain yearly. The presence of a sea at the foot of the range must have largely increased the rainfall, as has been pointed out. It is to be inferred from Professor Whitney's remarks that he supposes the climate of the Sierra to have been too warm for glaciers during the Tertiary. He regards the present climate, on the other hand, as too dry to permit of their formation, though there can be no doubt of their existence in the higher part of the range above the gold belt up to within a comparatively short time. A few small glaciers on the northern slopes of mount Shasta are now the only remnant of the former ice system of the state. The Sierra glaciers were of the mountain type, however, comparable at their greatest 'extension with those of modern Switzerland, and nothing like a general glaciation or a diluvial period ever existed in California. The following sections of auriferous gravel deposits are selected from a large number furnished by the reports of the special experts to illustrate the mode of occurrence of the gravels in various portions of the state : BONANZA MINE. MOKEL0MNE HILL DISTRICT, CALAVEEAS COUNTY, CALIFORNIA. I II III IV Lava cap in places. Alternating fine and coarse sand with pebbles (chiefly quartz) . Cement, sesquioxide of iron. Bed-rock, slate. A quartzose (also granitic and slaty) conglomerate, cemented with > Maximum, 123 feet; avetage, 75 feet. Richest portion nsnnlly lower 15 feet above bed-rock. ID place* gold nearly evenly disseminated throughout deposit. The ancient channel on which this mine is located is traceable, with intermittent breaks, for 10 miles. The channel is 500 feet wide, the outer edges barren, and the pay channel is 300 feet wide. o School of Mine* Quarterly, November, 1881. GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 13 LAGRANGE HYDRAULIC MINE. LAGRANGE DISTRICT. STANISLAUS COUNT Y, v CALIFORNIA. II m IV v Red sand Coarse red gravel, containing pebbles of granite, etc.. Red cement ( ' ' hard-pan "). White siliceous clay Red cement (same as HI) VI Sand with pebbles VII Loose yellow sand VTII Dark-colored gravel, containing dtbris of granite, argillaceous slate, " ser- Dentine," etc., with some quartz. IX Bed-rock at Lagrange "dioriteand, slate"; at Patricksvillc "basaltic tufa" (no specimen). ' Maximum, 300 feet ; average, 40 feet. Lowest 6 feet 8 inches riohest. Quartz forms but a small proportion of the gravel, which is chiefly granite, etc. Generally the upper workings do not pay, 90 per cent, of the gold being obtained from near the bed-rock ; but sometimes the upper horizon is the richest. At Patricksville, gravel is overlaid by tufa ; not much tnfaceons cropping at Lagrange. Ancient river bed. Deposit in patches for 1 mile wide by 2J miles long. LYON DRIFT MINE. PLACERVILLE DISTRICT, EL DORADO COUNTY, CALIFORNIA. I " Lava" or a consolidated sediment of volcanic origin 60-130 feet. II Mountain gravel 0-50 feet. m Granitic sand, in places consolidated 0-20 feet TV Gravel Maximum, 20 feet ; average, 3 j feet. V Bed-rock, slate. Three benches of ancient river, overlaid with volcanic matter, 60 to 130 feet wide, are here traceable for 3,000 feet. ORION MINE. IOWA HILL, PLACER COUNTY, CALIFORNIA. I Sand and fine gravel .... 1 ( n Coarser blue gravel >Maximnm,180feet; average, 100 feet, i \ All pays. Bichest near bed-rock. III Bed-rock, black slate, rough. No lava ; no quicksand. Ancient river bed, said to be 2,000 feet wide, traceable 2J miles. VAN EMMOXDS 1 MINE. MICHIGAN BLUFFS, PLACER COUNTY, CALIFORNIA. . , _ I Very little lava. II Fine gravel, alternating with sand strata , , HI Blue gravel I : All pays; but white gravel nearest TTT ' AVI , ,,.i ! Maximum, 50 feet ; average, 30 feet, { I bed-rock best IV >> Illtc g!M\ el...... ....................... V Bed-rock, rough slate ) ( Petrified wood, leaves of oak, pine, etc., found in sand strata. It is unusual to meet white gravel beneath the blue. MORRIS RAVINE MINE. MORRIS RAVINE DISTRICT, BUTTE COUNTY. CALIFORNIA. I Hard, solid lava cap in places. H Fine quartz gravel ! , III Kotten bowlders i I Maximum, 150 feet ; aver- I ! A little gold throughout. Blue gravel . , I age. 40 feet. richest. IV Bin-gravel 3-20feet..l V Bed-rock, chloride and clay slates, rough and decomposed. Pipe-clay occurs irregularly throughout deposit. Quicksand met with. SPRING VALLEY MINE. CHEROKEE DISTRICT. BUTTE COUNTY, CALIFORNIA. -^TZ ~ | . ~ I Lava cap over part of claim. II Fine quartz gravel 25-150 feet. ] ] III Rotten lm-l,l... s of yellow slat,, mixe.l with quartz gravel 5-15 feet, l' iva'a vel'.g, ' ' luo'feet. [ I! " 1 P a - v in KI and IV ^ d ~ r "^- IV . Blue gravel 15-SO feet. ) V lied rock, where exposed, described as '-b^^It" like the cap, probably inrtiunoi jiiiii-. Sarrouoiding country loi'lA shite. \Vutei- and quiekikind found in large quantities at the depth of 300 feet. Barren pipe-clay, 25 to 150 feet in places, as a rule overlying rich gravel. 14 PRECIOUS METALS. HUNGARIAN HILL MINE. PLTJMAS COUNTY, CALIFORNIA. I n III Soil Loose gravel, name character from surface to bed-rock Generally soft slate bed-rock; in places hard siliceous slate. Rough, with projecting points in some places rising nearly to surface. | , > Maximum, 110 feet; average, 75 feet. ) Gold thronghont gravel. All pays. Kiver bed, with rim-rock on each side, 250 feet wide; traceable, 3j miles. No lava, water, or quicksand. CARROLL DRIFT MINE. McADAU'S CREEK DISTRICT, SISKIYOU COUNTY, CALIFORNIA. I II III IV V VI VII Loam ,4 feet, I Loose tailings , 6 feet. Wash gravel, with clay and sand j 10 feet. Compact yellowish-white clay (water level) j 18 inches to 4 feet. Coarse yellowish gravel (bulk of deposit) j Qnartzoso matter J 3-6 inches. Greenish gravel 12 feet j, Maximum, 115 feet ; average 73 feet. j vm i Bed-rock, rotten brown slato and hard fine-grained blue slate. None barren, lint only a email portion pays for drifting. The pay streak is 200 feet wide and length of claim. Good pay. Best pny ou bed-rock and in bed-rock to a depth of 2 feet. Bed of McAdam's creek. Mining is carried on over a length of 34 miles by a width of 150 to COO feet. OAK GROVE DRIFT MINE. McADAM S CREEK DISTRICT, SISKIYOU COUNTY, CALIFORNIA. I n in IV v VI VII vin Loam 4 feet. Loose tailings 6 feet. Wash gravel, with clay and sand ! 10 feet. 18 inches to 4 feet. Compact yellowish clay (water level) Coarse yellow gravel Qnartzoso matter 4 to fl inches. Yellow gravel Bed-rock, brown slate, ridgy and seamy in places; in others soft and open. Average, 63 feet. None of the gravel is barren. Good pay. The best pay is 1 to 3 feet on bed-rock and 1 to S 'feet iu bed-rook. PACIFIC MINE. HUMBUG DISTRICT, SISKIYOU COUNTY, CALIFORNIA. n m IV v Loose wash gravel Coarse yellow gravel, containing many large bowlders Fine sand Yellow gravel 20 feet. Dark yellow gravel [l foot. 5 feet 8 feet, Inches to 2 feet. ( Maximum, 50 feet; average, 45 feet. VI | Bine gravel 8 inches to 10 feet. . VII i Bed-rock, bine slate. Contains but little gold. None barren. > Best pay. River bed traced for 1 mile, average 50 feet wide. BUNKER HILL MINE. DEL NOKTE COUNTY, CALIFORNIA. I II HI IV Red loam mixed with fine gravel Loose gravel Gray cement streak, 60 feet wide. Large bowlders in best ground "Serpentine" bed-rock easily piped, having bine slate under it (Leavens). Specimen determined as highly metamorphio dioritic-looking rock. 15 feet. 1 Maximum depth of bank, 125 r f ep ,t I feet; average, 80 feet. Maxi- (None of the gravel is barren, bnt the [ mum depth of gravel, 50 feet; [ richer portion is near bed-rock. 20 feet, j average, 30 feet. Channel one-half to three-quarters of a mile, 150 feet long ; course a little west of north. Large deposits of copper ores have been found in the auriferous slate series, especially in Calaveras county. Oopperopolis is the principal point, but there are also deposits at Campo Seco, and again further north near lone City. Prospects have also been found on the same line beyond this point. The ors are native copper and carbonates near the surface, replaced by a mixture of iron and copper pyrite below the water-line. The deposits have the same dip and strike as the inclosing chloritic slates. Extensive shipments were made in former years. Mono and Iiiyo counties, though politically united to California, considered from a physico-geographical point of view, form a portion of the Great Basin. The sedimentary rocks of Mono county appear to be Mesozoic, but the western edge of the great Palaeozoic area which covers the eastern portion of the Great Basin crosses the California, line about due south of Columbus, Nevada, passing near Owen's lake and then diverging to the southeast. Great quantities of lava are met with in both counties, as throughout the Great Basi* The deposits of these counties also GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 15 bear a much closer resemblance to those of Nevada thaii to those of central California. The best known mining localities are Bodie, Cerro Gordo, and Panamint, but noHe of them have formed the subject of any detailed geological investigation. The bullion of Bodie is usually regarded as gold, because its silver contents are much less valuable than the accompanying gold. Keports made to the director of the mint for the year 1880 show that from 5 to 63 per cent, of the value of the bullion produced by the various mines was silver, which also formed 17.91 per cent, of the value of the total product ($3,063,699 13). It follows that from 45.7 to 96.5 per cent, of the weight of the bullion from different mines and 77.72 per cent, of the total weight was silver. In 1879, when a smaller portion of the colorados were worked out, silver only formed 65.2 per cent, of the entire weight. Bodie metal may therefore very properly be regarded as a highly dor silver bullion, similar to that of the Comstock lode, and as essentially different from that of the gravel and slate region ordinarily known as the gold belt. The Comstock was at first worked for gold. The Bulwer, the Syndicate, and the Standard Consolidated, which show but little silver, are on top of a hill where the water-level is far from the surface and the quartz is reddened to a great depth ; the Bodie Consolidated, Noonday, and others are at lower elevations. The sulphurets of these mines are not oxidized, and the bullion shows a large amount of silver. The gangne minerals of these deposits are base sulphurets, quartz, and calc-spar. They are inclosed in extremely decomposed rock, bearing clear signs of solfataric action. The rock is so highly altered that tolerably fresh specimens are not obtainable near the mines. Slides of the freshest specimens collected are not decisive as to the character of the rock. They show plagioclase, and apparently some orthoclase, accompanied by mica and a little hornblende; the ground mass also contains quartz. Only a detailed examination in the field will decide what name the rock should bear. The mines of Cerro Gordo were not in operation during the census year. The deposits, which at one time were very productive, were masses of argentiferous lead ores occurring in limestone, and consisting for the most part of carbonate, sulphate, and other decomposition products of galena. Schists and slates were also met with in the mines, ;is well as a granite-porphyry. This is said to occur as a dike in the Union mine and elsewhere, and is locally called syenite, though it is qtiartzose and micaceous. Panamint was for a short time a very flourishing camp, its prosperity being derived from veins in limestone carrying chiefly argentiferous gray copper ore or freibergite, associated with galena and zincblende. Mining is still being carried on, but the richer deposits were soon worked out. The age of the limestones of Cerro Gordo and Panamint is unknown. Both districts lie near the contact between the Palaeozoic and the Mesozoic, and may belong to either; but limestones are exceptional in the Trias and Jura of the Sierra region, while they predominate in the Palaeozoic area. Gold has been found at a great number of points in the Coast ranges proper and in the western ranges of southern California. No doubt large individual profits have been made at certain localities, and it is by no means impossible that as good or better veins than those found await discovery. It is scarcely likely, however, that after thirty years of skillful prospecting any important gold-mining region has escaped observation. A few years since great hopes were raised by the prospects on* veins in the slates and on the contact between slates and granite in the Julian and Banner districts near San Diego, but they have fallen short of the expectations excited. ' The so-called Gold Bluffs along the coast of the northern counties, especially near the mouth of the Klamath river, are bluffs which contain extremely small quantities of gold, and seem to be beds of detritus left by the shifting of the river channels. The sea encroaches upon them, and when the surf strikes the beach in certain directions and with a certain strength the gold is concentrated in comparatively rich sands, which are gathered and treated in apparatus of various designs by amalgamation. The only quicksilver ore of great importance is cinnabar, although metacinnabarite, the black sulphide, is rather abundant in a few mines, and metallic quicksilver sometimes accompanies the deposits of its compounds. The metaoinnabarite described by Dr. G. E. Moore was amorphous, but according to Mr. Goodyear it also occurs as minute crystals. Cinnabar is found in a great number of localities in the Coast ranges for 100 or 150 miles north and south of San Francisco, always, so far as known, ill metamorphic rocks of Cretaceous age. The character of the metamorphism is generally peculiar, and the so-called quicksilver rock is readily recognizable. It is a silicitted chert like material, often reddened by iron oxide, and usually accompanied by serpentine or serpeutiuoid matter. In almost all cases pyrite or marcasite and bituminous matter accompany the cinnabar, and mispickel and copper pyrite are reported in a few instances. At Sulphur Banks, on Clear lake, native sulphur occurs in great quantities with the quicksilver ore, and native gold has been found in water- worn masses of cinnabar not far from the same locality. The converse occurrence of cinnabar in two of the quartz veins of the Sierra gold belt has already been noticed. Stibnite is reported as occurring with cinnabar at the Lake mine near Knoxville. The usual gangue minerals are quartz, calcite, and magnesite. Cinnabar does not occur in well-marked veins, but generally in irregular bodies distributed through the rock. In the New Almadeii mine, which has been much more extensively woi ked than any other in the state, these bodies appear, from a model constructed by the owners, to lie on a curved surface, indicating a geometrical relation between the positions of the several ore-bodies, though an obscure one. At this mine the masses of ore are usually connected by tiny seams of the same material. There is a strong similarity between this mode of occurrence and that of many lead ore deposits in limestone, and it may be that the problem of their tme character is the same. 16 PRECIOUS METALS. The quicksilver country north of San Francisco is a volcanic region, while to the south volcanic rocks are subordinate in some localities and wanting in others. To the south, too, there is no indication of any recent deposition of the ore, while to the north deposition is still actually in progress. No general inference as to the genesis or the age of the deposits can therefore be drawn without further investigation, while the great similarity in the association of minerals suggests a similar origin for most of them. The Sulphur Banks, on Clear lake, forms the subject of a recent paper by Professors Le Conte and Rising, (a) At that point cinnabar with pyrite and some bituminous matter, as well as free sulphur, is now being deposited. The hot waters rising to the surface are charged with sulphides of ammonium and of the fixed alkalies, and appear to carry in solution cinnabar and pyrite, which are deposited, in the opinion of the authors, by reduction of temperature and pressure, probably assisted by neutralization through the percolation of free sulphuric acid from the surface. The deposition of sulphur is a surface phenomenon. It may also have attended the formation of the deposits to the south of San Francisco and Lave been subsequently removed by erosion. The only Californiuii coal-fields of great importance are those near Monte Diablo, which occur in sandstones of the Upper Cretaceous or Tejon group. According to Professor S. F. Peckhain's examination, (/>) these coals carry from 5 to 11 per cent, of ash, 4i to 5.J per cent, of sulphur, and from 11 to 13 per cent, of water. The refuse dumps of these mines frequently take fire spontaneously from the oxidation of pyrite. Coal of the same age occurs under less favorable conditions at Corral Hollow, in the Monte Diablo range. Seams are fonnd here and there all along the Coast ranges, but they are usually thin, and even when of a workable thickness are so faulted and broken as to be of small value. Lignite of Pliocene age is found at lone valley, Amador county, and is used along the line of the railroad to some extent at Dog creek, near the Truckee river. In southern California there are vast quantities of bitumen, from which asphalt and a certain quantity of illuminating oils are obtained. The bitumen occurs in shales of the Miocene, which are in large part too much disturbed to permit of the accumulation of pressure necessary to induce flowing wells. Many of these bitumens, though thin as they issue from the gronud, oxidize and are converted into hard asphalts. According to Professor Peckham, the California bitumens are composed of a different series of hydrocarbons from those which make up the petroleums of Pennsylvania. AMADOR COUNTY. This county lies directly across the main gold belt. Quartz mining takes the first rank, though there are gravel deposits, and hydraulic mining is carried on to a considerable extent. The gold in the veins is associated with iron and copper pyrite, marcasite, mispickel, and small quantities of galena. The gangue is chiefly quartz, but some calcite is occasionally found in the veins. The country rocks are slate and granite, the former being predominant, but a greenstone also occurs, which, though much decomposed, is probably a diabase or proterobase. The mother lode has been traced with certainty from Mariposa to about the center of Ainador. Copper is found in the western portion of the county, but it is not at present worked, and a lignite o&curs at lone City which is of considerable local importance. AMAUOK. [NOTE. Determinations in parentheses are given on the authority of the experts.] Mine. Ore anil gangue. WALLS. Foot. Hanging. AMADOU CITY. Keystone (Gold, chalcopyrite, galena), pyrite and quartz . .' Proterobase (?) * Proturobase (?)*. JACKSON. Monte Richard (Gold), iron-stained quartz (Greenstone or augite-por- Proterobase phyry, called granite.) Oru-ida (Gold, galena, chalcopvrite, ami marcasite). pj rite Grcenot one, probably an au- do and quartz. gite-porphyry. Zcile i (Gold, pyrite, rarely galena and cbalcopyrite, quartz) . (?) , Qoartzite PLYMOUTH. I'lu-itic Mining Company (Gold), indeterminable black sulphurets and quartz (Kmpire, etc., mines). SUTTEH CREEK. Consolidated Amador (Gold, galena, chalcopyrite, mispickel), pyrite and I (Clay mic:v elate) (Talcose slate) . quartz. VOLCANO. Madeira (Gold), galena, calcite, and quartz. Character of deposit. Vein. Vein. Do. Do. Vein. Vein. * Examined microscopically. a American Journal, vol. 2-4, v>. 2:1, 1882. l> Ceoloyical Surrey of California: Geology, II, p. 44. GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 17 BUTTE COUNTY. A large part of Butte county lies in the Great Valley, and produces no gold; but the eastern portion contains extensive gravel deposits, which are continuations of those of Plumas and Yuba. Much of the gravel is covered by a cap of basalt, and the bed-rock is, in all the cases reported, sandstone or metamorphic slate. BUTTE. [NOTE. Determinations in parentheses are giren on the authority of the experts.] w^ LL6. ' Character of Mine. Foot. Hanging. deposit. CEXTERVILLE. Basalt cap* Placer. CHEROKEE. (Gold gravel) ... .... Altered diabase* Do. ' Examined microscopically. CALAVERAS COUNTY. Both quartz and gravel mining are actively pursued in this county, which lies across the gold belt. The auriferous quartz carries iron and copper pyrites, mispickel, galena, and zincblende. The wall rocks in all the cases reported are metamorphic. The mother lode crosses this county. The gravel is of the ordinary character, and, as usual, is accompanied by more or less basaltic lava. Copper deposits occur below or to the west of the gold belt at and near Copperopolis. CALAVEKAS. [NOTE. Determinations in parentheses are given on the authority of the experts.) Mines. Ore and gangue. WALLS. Character of deposit. Foot. Hanging. AXGEL'S. Vein. Do. MOKELUMNE HILL. Gwin (Gold, mispickel, zincblende), pyrite, chalcopyrite, and quartz. (Black slate) (Black slate) DEL NORTE COUNTY. Auriferous gravels are the chief metalliferous deposits of this county, the bed-rock consisting of slate and other sedimentary strata. Beach sands are also worked to a small extent on the coast. DEL NORTE. [NOTE. Determinations in parentheses are given on the authority of the expert.] WA LLS. Character o Foot. Hanging. deposit. Bunker Hill (Goldgravel) Placer China Creek .do Do. Del Norte ....do Slate Do Happy Camp ....do do Do Muc-a-muc ....do Shale Do. Wingate ....do Slate Do. VOL 13 2 18 PRECIOUS METALS. EL DORADO COUNTY. El Dorado lies across the gold belt, and contains a great deal of gold quartz, while the placers are comparatively insignificant. Some of them, however, buried under heavy caps of lava, are profitably worked by drifting. The gold quartz carries the usual sulphurets, pyrites, mispickel, and zincblende. The country rock is chiefly slate. Copper ores also occur in the western part of the county. EL DORADO. [NOTB. Determinations in parentheses are given on the authority of the experts.] Mine. Ore and gangue. WALLS. Character of deposit. Foot. Hanging. FLACEBVILLB. (Gold gravel) Slate Lava cap, basalt, pumice* .. Placer. Vein. Do. Gold, pyrite, mispickel, quartz, (zincblende and ga- lena). (Slate) ... (Slate) . ' Examined microscopically. FRESNO COUNTY. Fresno extends from the crest of the Sierra to the Coast ranges. It lies to the south of the main gold belt, but 'contains a few gold quartz veins in the Potter ridge district and elsewhere, carrying the usual sulphurets, and being inclosed in slates. At the western edge of the county is the famous New Idria quicksilver mine, in which cinnabar is accompanied by pyrite and bituminous matter. According to Mr. Goodyear, the ore does not occur in a vein, at least of the typical character, but in irregular bodies, distributed in metamorphic sandstone and shale. FRESNO. [NoTK. Determinations in parentheses are given on the authority of the experts.) Mine WA I.LB. Character of Foot. Hanging. deposit. SAN CARLOS. New Idria Cinnabar, (pyrite, chalcopyrite, and bitumen) Vein POTTEB BIDGR. Fresno Enterprise (Gold, sulphurets, and quartz) (Slate) (Slate) Do HUMBOLDT COUNTY. There is no gold quartz mining in Humboldt, and the placer mines are not extensive, compared with those of the central counties. The gravels appear to represent modern river bars of the Klamath, along the banks of which they are -found, in some cases, however, at a very considerable elevation above the present stream. As in Del Norte, there are auriferous beach sands, which can be worked with profit when certain combinations of wind and waves have effected a preliminary concentration of the auriferous material. INYO COUNTY. The most important mines in this county carry argentiferous lead ores with calcareous gaugue. They occur either in limestone or in limestone associated with granite and schist. The deposits are chimneys, or bodies of an irregular form, such as lead ores frequently assume elsewhere. Copper ores, associated with those of lead, also occur. Where copper is the principal constituent the gangue is usually siliceous. The copper veins occur in limestone or in granite, or on the contact between the two. The lead ores are galena, cerussite, anglesite, and probably lead ocher, accompanied by argentite and other silver minerals. The copper ores are chalcopyrite, stromeyerite, tetrahedrite, bornite, and carbonates. They are usually argentiferous. In addition to the gangue minerals mentioned, fluorite is found in the Defiance mine, in a silver-lead deposit between granite and limestone. There are also gold-quartz veins in granite in the county, and some small gold placers. At the Lee mine argentite and horn-silver are reported as occurring in limestone. GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 19 INTO. [NOTE. Determinations in parentheses are given on the authority of the experts.) Mine. Ore and gangue. WALLS. Character of deposit. Foot Hanging. CEBBO GOBDO. (White limestone) Schist (white limestone). Marble. do. Vein. Vein. Do. Do. Do. Bedded vein. Vein. Bedded rein. Vein. Flat vein. Vein ; also small placer. Deposits. Marble do ....do ) J i Granite, porphyry dike *. > (Granite) . . CO8O. Galena, cenissite, chalcopyrlte, malachite, fluorspar, calcite, and pyrite. Siliceous limestone do (Granite) New Coso Company (includ- ing Lucky Jim and Christ- mas Gift). Limestone (containing bari- nm). (Granite) (Granite) Limestone and schist KEARSABGE. Cernssite, micaceous iron, limonite, (tetrahedrite, cerargyrite, and argentit*), qnartz. Stromeyerite, (tetrahedrite, galena, pyrite, and zinc- blende), quartz. (Cernssite, carrying gold and silver, with arsenic and antimony ; calcite, iron oxide, and manganese min- erals.) (Cernssite, galena, bornite, malachite, pyrite, and quartz.) Granite* Granite* PANAMCTT. (White limestone) LOOKOUT. Modoc Consolidated KUSe. FISH BPRIMGS. Golden Wreath, Granite Granite (Gold quartz) (Granite) (Granite) Lee (Limestone) ... (Limestone) * Examined microscopically. KERN COUNTY. Kern county lies south of the main gold belt ;' it nevertheless contains some gold-quartz veins in its northeastern portion, in the Sierra range, as well as some shallow placer gravels. LAKE COUNTY. The only important mineral di-posits of Lake county are those of quicksilver, which occur at a number of points in considerable quantities, accompanied by pyrite, sulphur, bituminous matter, and quartz. The inclosing rocks are metamorphic. The deposits are associated in some cases with basalt. LAKE. [NOTE. Determinations in parentheses are given on the authority of the experts.] Mine. Ore and gangne. WALLS. Character of deposit. Foot. Hanging. Vein. Irregular deposit. EAST LAKE. Sulphur Banks (Cinnabar, native sulphur, bitumen, pyrite, borax, alum, and quartz.) Sandstone and basalt Sandstone and basalt. 20 PRECIOUS METALS. LASSEN COUNTY. This county contains gold-quartz mines. The veins are associated with rocks which are in part raetamorphic and probably also in part eruptive, but the specimens in the collection are so decomposed as to be indeterminable. Enormous quantities of lava cover much ground in this part of the state that would probably otherwise be remunerative. LASSEN. [Nora. Determinations in parentheses are given on the authority of the experts.] Mine. Ore and gangne. WALLS. Character of deposit. Foot. Hanging. IIAYDKH HILL. Vein. Do. Ho , ... do .. do - LOS ANGELES COUNTY. There is some silver mining in this county. Antimonial silver ores and argentiferous galena occur with pyrite, copper ores, and quartz inclosed between wall rocks which are chiefly sedimentary, but probably in part eruptive. Asphalt, petroleum, and coal, as well as salt, are also found in the county. LOS ANGELES. [NOTE. Determinations in parentheses are given on the authority of the experts.] Mine. Ore and gangue. WALLS. Character of deposit. Foot. Hanging. SILVERADO. Bine Light Galena, pyrite, and quartz.. - Limestone and quart zite Quartzite Limestone and quart zite .... Shale. Probably diorite. Vein. Galena, zincblende, pyrite, (antimony and copper stains). do Phojnix . . MARIPOSA COUNTY. This is the most southerly county on the gold belt, and contains many gold-quartz veins inclosed in slate. Argentite, proustite, and (it is said) silver telluride are also found. The southern end of the mother lode is in this county on the famous "Mariposa estate". MABIPOSA. [NOTE. Determinations in parentheses are given on the authority of the experts.] WA .L8. Character of Foot. Hanging. deposit. MAHIPOSA. Hiti (Free gold, galena, copper pyrite, occasionally gold; Vein ' BEBASTAPOL. Modesta pyrite, zincblende quartz, telluride ore.) Coe { Slate) Vein NAPA COUNTY. In this as in the adjoining county, Lake, the principal useful mineral found Is cinnabar, which occurs in the usual serpentinoid and arenaceous metamorphic strata. The Kedington mine is one of the most important quicksilver producers in the state. GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 21- NAP A. [NOTE. Determinations in parentheses are given on the authority of the experts.) Mine. Or* and gauguo. WALLS. Character of deposit. Foot. Hanging. OAT HILL. Cinnabar, with sandstone and clay, (bituminous mat- ter). Cinnabar, metacinnabarite, marcasite, bitumen, quartz, (mispickel). Sandstone Vein. Irregular bodies. Schist MONO COUNTY. This county seems to contain two classes of deposits. The highly dore" silver, or low-grade gold of Bodie, is found in eruptive rocks of as yet undetermined character. A portion of the gold is free, but a large part of it is associated with complex silver sulphides, accompanied by quartz and calcite as gangue minerals. The other districts are granitic and carry chalcopyrite, copper glance, and carbonates, with galena, zincblende, argentite, and other silver minerals. MOM). [NOTB. Determinations in parentheses are given on the authority of the experts.] Mine. Ore and gangne. WALLS. Character of deposit. Foot. Hanging. BLIXl) SPRING. Copper glance, chalcopVrite, zincblende, probably tetrahedrite, chrysocolla, (partzite, malachite, clay, and quartz). Copper glance, chrysocolla, copper carbonates, limo- nite (partzite and malachite), with earthy and (de- composed granitic gangne). Copper glance, chrysocolla, copper carbonates, (ga- lena and horn-silver). Granite Vein. Do. Vein. Do. Do. Do. Do. Do. Do. Do. Do. Do. Do. Vein. Do. Vein. Do. do do Modoc ItODIK. do Bulwer (Quartzose and feldspatuic vein matter carrying gold and silver.) McCliuton do Oro Standard Consolidated (Gold and silver bearing quartz) do do (Gold silver quartz and feldspathic matter) (Volcanic) (Volcanic) HOMKR. Maybell (Gold, silver, iron pyrite, galena, and quartz) do Granite 1NU1AX. ^Granite and porphyry) do (Granite and porphyry) do Galena, zincblende, native silver, tetrahedrite, (pyrar- gyrite, pyrite, and quartz). NEVADA COUNTY. Nevada has always been one of the most productive counties in the state, both the quartz and the placer mines yielding very large amounts. The quartz mines are for the most part in the slates characteristic of the main gold belt, but some of them are in granite, and some of them are on the contact between gran-ite and slate. The gold is accompanied by iron and copper pyrites, mispickel, galena, and zincblende. As elsewhere in the gold belt, the proportion of silver is extremely small, even by weight. Though the larger part of the gold is free, the sulphurets are ordinarily much richer than the quartz taken as a whole, and it usually pays to concentrate them and subject them to the Plattner chloridation process. The placer deposits are in part covered by volcanic rocks, chiefly basalt. The cap over a large area, however, is not so deep as to prevent the gravel from being worked, as it does to a considerable extent in the counties further north, while the amount of volcauic material has been sufficient to protect the gravel from extensive erosion. One of the great Tertiary rivers flowed through this county in a southwesterly direction and gave rise to the large gravel accumulations. 22 PRECIOUS METALS. NEVADA. [Nora. Determinations in parentheses are given on the authority of the exports.] Mine. Ore and gangne. WALLS. Character of deposit: Foot. Hanging. GRASS VALLEY. Idaho .. . Free gold, galena, iron and copper pyrites, and some- times zincblende, quartz. Gold, pyrite, zincblende, galena, quartz, (copper pyrite). (Gold), pyrite, (zincblende, galena, iron, and copper pyrito), quartz. Pyrite and quartz. (Gold), pyrite, (galena, copper, and iron pyrite), quartz. (Gold, iron, nnd copper pyrito, galena, zincblende, and quartz.) Magnesian metamorphic rock. Slate Magnesian metamorphic rock. Slate Vein. Do. Do. Vein. Do. New York NEVADA CITY. Merrifleld Granite . ... Granite . . do PLACER COUNTY. Placer lies directly across the gold belt, and is one of the principal producing counties. The gold-quartz veins occur for most part in slates, though some are found in granite, and they present the usual association of sulphurets. The auriferous gravels have been sufficiently protected by volcanic material to escape radical erosion without being so deeply covered as to be inaccessible. Iron-ore deposits are abundant. PLACER. [NOTE. Determinations in parentheses are given on authority of the experts.) Mine. Ore and gaiigne. WALLS. Character of deposit. Foot. Hanging. COLKAX. Rising Sun (Granite) (Granite) Vein. PLTJMAS COUNTY. The gold belt in the latitude of Plurnas county is not so sharply denned as further south. Deposits of the precious metal, however, are abundant, both as veins and in gravel. The association of sulphurets accompanying the gold is the same as in Nevada county. The wall rocks are either slates and other metamorphic rocks or granite or both. The slaties are sometimes so intersected by auriferous quartz as to give the veins a reticulated character. Although the production of the placer mines is considerable, a large part of the gravel is supposed to be inaccessible through the presense of heavy overlying sheets of basalt. PLTJMAS. [NOTE. Determinations in parentheses are given on the authority of the experts.) Mine. Ore and gancue. WALLS. Character of deposit. Foot. Hanging. CHEROKEE. Plnmas Eureka Metamorphic diorite * Slate Metamorphic diorite * Slate Vein. Reticulated vein. Veto. Do. Do. Do. Vein. Placer. GENEBKE VALLEY. Gcncsee (Gold) , slate and quartz INDIAN VALLEY. Gold Stripe (Gold generally free from sulphurets) qnartz (Slate) Green Mountain (Gold, pyrite), quartz (Decomposed granite) (Granite) Slate (Decomposed granite) (Slate) Slate Monitor Dumas National (Quartz), pyrite and mispickel BENECA. Savcrcool (Gold), pyrito sandstone, and quartz (Clay slate) Sunnyside Gravel (Auriferous gravels) P * Examined microscopically GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 23 SACRAMENTO COUNTY. The oxide.) do do wulfenite, with limonite and aragonite gangue. pipe veins. Phcenix J ....do.. ... do and iron oxide.) Shale. SECRET CASON. Irregular maas. EUIIEKA. oxide. Limestone. HUMBOLDT COUNTY. Most of the veins are in the Mesozoic slates, and carry ruby silver and stephanite with iron and copper pyrite and mispickel in a quartz gangue. Near the croppings the silver takes the form of chloride. Some of the veins in the slates are worked for gold, but of these a part will probably be found to carry more silver than gold when the water-level is passed. The Pride of the Mountain, Winnemucca district, is reported to be on a contact between slate and granite. PRECIOUS METALS. HUMBOLDT. Determinations in parentheses are given on the authority of the experts.] Mine. Ore and gangno. WALLS. Character of deposit. Foot Hanging. MOUNT ROSE, OB PAKADI6E. Big Nick Slate Slate Vein. Do. Do. Do. Vein. Contact vein. Bullion of Paradise Chloride, pyargyrite, (rn by and stephanite) ; pangue quartz, p'yrite, mispickel, chalcopyrite, and iron oxide. do .. do . do. . do do ....do .. do SIERRA, OB DUN GLEN. Silicifiod sedimentary rock (called porphyry). (Slate) Silicifled sedimentary rock (called porphyry). (Slate) WINXEMUCCA. (Snlphurets and antimonial silver minerals, with quartz gangue.) (Slate) (Granite) LANDEK COUNTY. Besides the Austin mines, sufficiently described above, there are veins of ruby silver, etc., in quartzite, and of galena with quartz gangue in Palaeozoic slate. LANDEK. [NOTE. Determinations in parentheses are given on the authority of the experts.) Mine. Ore and gangue. WALLS. Character of deposit. Foot. Hanging. BATTLE MOUNTAIN. Slate Vein. Vein. Vein. LEWIS. KEEBE EIVKR. Dark and light ruby silver, stepbanito, polybasite, tetrahedrite, galena, iron and copper pyrites, and quartz. Granite* * Microscopically examined. LINCOLN COUNTY. This county shows several classes of deposits. There is a considerable number of occurrences of galena and its decomposition products in limestone similar to those of Eureka, uud elsewhere, and which seem especially abundant in the Palaeozoic limestone of the Great Basin. The Meadow Valley and .Raymond & Ely are also in metamorphic strata; but these are quartzites, not limestones, and the character of the ore is correspondingly different. Below the water-level the ore consists of sulphurcis of unspecified composition; above the water-level it carries horn-silver, some gold, a little lead, and manganese. In the Eldorado district there are mines in a massive rock, probably diorite, which carry argentiferous copper minerals. LINCOLN. [NOTE. Determinations in parentheses are given on the authority of the experts.] Mine. Ore and gangue. WALLS. Character of deposit. Foot. Hanging. BRISTOL. Hillside Limestone. Granite. Li m oat one. I'robuHy dioritf. Granite * : Limestone Vein. Pockets. Vein. Do. Quartz-porphyry and shale. . Mendha El.DOBADO. Januarv .... (Horn-nil vcr), iron oxide . Srromeyt'i it i 1 , quart/, ami f-alcitc Argentiferous ^al^na aud lead carbonate, red copper oro HIM! malachite, manganese o\'Kio, (cale-spar aud iron oxide). (Gold. horn-allver, quartz, iron oxide, and manganese oxide.) ....do Probably d iorite Granite*. LiUH'HtolU! Savage JACK BABBIT. Dav ELY. Meadow Valley - Raymond Si Ely do do Brooklyn Galena, ziucblemle, iron pyrites, (antimouial silver aud quartz). Silicrous limestone. MiiTosconii ally examined. GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 37 NYE COUNTY. Argentiferous lead ores, inclosed in limestone in the usual irregular masses, veins of silver and copper ores, accompanied by slate or granite as well as limestone as wall rocks, and veins of arsenical and antimouial silver ores, inclosed in quartz-porphyry, are all found in Kye. The famous Belmont mine is on a vein in Silurian slate which lies between granite and limestone. The vein is conformable with the slate, and carries sulpho-salts of copper, silver, and lead. NYE. (NOTE. Determinations in parentheses are given on the authority of the experts.] Mine. Ore and gaogne. WALLS. Character of deposit. Foot. Hanging. BELMOXT. Galena, probably stephnnite, qnartz, pyrite, (sulphur- eta of lead, copper, and silver). Sulpbnrets, arsenical and antimouial silver minerals and mispickel. Knby silver anil sulphnrets, arsenical and antimonial silver minerals, aud manganese spar, do Slate between granite and limestone. Quartz-porphyry * Slate Vein. Vein. Do. Do. Contact vela. Mineral belt. MORKY. Quartz-porphyry * do do ...do ... do TIBO. Tybo Consolidated Galena and decomposition products, (horn-silver, iron oxide, quartz, aud argentite). Galena, horn-silver, (copper ores, native silver, lime- stoiio, and quartz), shale, zincbleudc, and iron oxide. Limestone Limestone I/kncstone CX1OH. * Microscopically examined. STOEEY AND LYON COUNTIES. The only mines of importance in these counties are 1ho.se of the Comstock lode, of which sufficient mention has been made. There are, however, other silver-bearing veins in eruptive rocks of this region, though none which yielded large and steady profits. STOREY AND LYON. Mine. T11E COS18TOCK Ore and gangne. Foot. Hanging. Auriferous quartz . Qnartz, argentitc, native silver, and gold, occasionally stephanite, polybasite, etc., iron and copper pyrile, rarely calcite. . Diorito * . Utah Peytona Sierra 7, evada Union Consolidated Mexican Opbir C;.,iiurnia I 'nu'-nlidnted Virginia Belcher (ioiild fe Curry I 1 ul" & Nnrcross Clir.llar Potosi Bullion Exchequer Alpha Challenge Confidence Yellow Jacket Kentnck Crown Point I't-lrlu-v Overman... -.do Quart z-porpbyry,* diorite,* Dlorite * ...do*.. Qnartz, argentite, native silver, and gold, occasionally J stephanite, polybaaite, etc., iron and copper pyrite, > Black slate " rarely calcite. ) A Ha ... do JiiMiei; : Rebellious silver ores in calcareous ganguc Qn: rtz- * Microscopically examined. and metamoipbics.* .do "auclmeta- Diorite ...do*.. Diabase* Diablo" Character of deposit. Vein. Do. Do. Diabase in part * . Diorite* ami andi'nit* Diont.' ' and andesite * Do. Do. Do. Do. 38 PRECIOUS METALS WHITE PINE COUNTY. The famous deposits of the White Pine district consist largely of horn-silver in irregular bodies in Devonian limestone. The chloride is accompanied by some lead minerals, however, and these predominate in the deposits of the base metal range near by. It is possible that the horn-silver of the Ebcrhardt & Aurora is a product of the decomposition of argeutitc, and it is distinguished from ordinary occurrences in limestone by the presence of large quantities of quartz gangue, but the admixture of lead minerals suggests that the ore bodies may be nearly related to the class of which the Eureka deposits are representative. There are also veins in the county associated with slate and massive rocks as well as limestone. These for the most part carry copper, besides silver and some gold". In the Eobinson district there are mines the ore of which is smelted for copper. They carry gold and silver in addition to the copper, and may represent extreme cases of the miueralogical association last mentioned. WHITE PCfE. [NOTE. Determinations in parenthesis are given on the authority of the experts.] Mine, Ore and gangne. WALLS. Character of deposit Foot Hanging. CHEEKY CREEK. Diorite (?) Contact vein. Vein. Contact vein. Vein. Impregnation. Do. Stir Slate Slate Ticknp Copper carbonates, sulpbnrets, (horn-silver.and quartz) Probably tetrahedrite, with carbonates Limestone ....do... KEWAHK. Limestone Limestone. Limestone WAliD. Probably stromeyerite and snlpbantimonifles, quartz, calc-Bpar, pyriie, zincblende, and cbalcopyrite. Slato, limestone, and prob- ably granite. WHITE PINE. ....do ....do The remaining counties are of little importance at present. Washoe is one of the oldest mining counties, and contains base metal mines and silver veins, but its product is now very small, while the resources of Douglas, Ormsby, and Koop are undeveloped. GEOLOGICAL SKETCH OF UTAH. In northern Utah the Wahsatch range trends approximately north and south. It ends to the south about latitude 39 30', but is nearly continuous with the western edge of the high plateau, which sweeps to the westward as the latitude diminishes. Together they form the eastern limit of the Great Basin, and divide Utah into two unequal parts, of which the western is the smaller. These two portions of the territory differ greatly. The Great Basin in Utah is characterized by the presence of the Great Salt lake and extensive areas of especially desolate alkaline desert, as well as by the system of mountain ranges mentioned in the description of Nevada. To the east of the basin lies an elevated area, of which the distinguishing characteristic is the horizontally of its strata. The general character of this region is that of a great undulating plain, though it is not utterly devoid of hills. Its soft surface is deeply carved by modern streams into fantastic pinnacles and bluffs, which, added to the prevailing extreme barrenness, gives it a strange aspect, and a large portion of it has received the significant name of "bad lands". This plain is broken in latitude 40 30' by the great eastern and western ranges of the Uintah mountains, which are 150 miles long, and rises at its culminating point, Emmons peak, to an elevation of about 13,700 feet. It is unlike any other range in America, being, in fact, a lofty forest-covered plateau, from which rise bare rocky peaks, composed, like the plateau, of nearly horizontal strata. It divides the Green River basin from the great plateau basin of the Colorado, but is cut through by the Green river. These two areas share the characteristics just described. The mineral resources of Utah are extensive and varied, and comprise lead, silver, gold, copper, coal, iron, salt, sulphur, etc. All the government surveys have done more or less work in Utah, but so far as the mining regions are concerned the chief sources of information are the publications of the exploration of the fortieth parallel and the geological volume of Captain Wheeler's survey. Dr. J. 8. Newberry has printed important papers on the subject, and Mr. G. JL Gilbert has published a paper on lake Bonneville.(a) The Wahsatch forms the boundary between two distinct geological regions. At the close of the Carboniferous the western portion of the Great Basin (including the area of the Wahsatch) was raised above the level of the a Second Annual Report Director United States Geological Survey. GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 39 ocean, a position which it maintained throughout the Mesozoic era. The regin to the east of the Wahsatcli. on the other hand, remained undisturbed during the Trias and Jura, and underwent only gentle changes of elevation during the Cretaceous. The post-Jurassic upheaval, which folded up the Sierra Nevada and the Basin ranges, probably also had its effect upon the Wahsatch, but extended no farther. At the end of the Cretaceous a vast upheaval took place in the heart of the country, by which the whole system of the Rocky Mountain ranges was raised substantially to its present position, displacing the great gulf which had hitherto occupied this area. In this uplift the Wahsatch was involved, as is known, by the plication of the Cretaceous strata ou its eastern slope; but the effect of the movement is not traceable further to the west. The Wahsatch range thus belongs geologically both to the system of the Basin ranges and to the Rocky Mountain system, and forms a broad boundary wall between the two. A great fault has taken place at the western side of the Wahsatch, which forms its foot wall. Had erosion not modified the range, it would be seen to consist of Mesozoic and earlier strata continuous with those of tlie country east of it but bent upward near the fault-plane, so that on the west of the crest there would be a gigantic cliff, cutting the strata nearly at right angles, while the eastern face would slope steeply away from the crest, but would gradually flatten and pass over into the nearly horizontal surface of the plateaus. To the south of fhe Wahsatch the plateau country was also elevated at the close of the Cretaceous, but its uplift was not attended or followed by any horizontal thrust sufficient to flex the strata near the line of upheaval into mountains. The Uintah range likewise dates from the post-Cretaeeous uplift, and indicates a northern and southern compression, for its character is that of a broad anticlinal. Since the post Cretaceous there have been further orographical changes, though none which have introduced new topographical features of importance. The great Wahsatch fault is a feature of the geology of Utah which has probably had an important influence on many of its geological phenomena, including that of mineral deposition. The geologists of the fortieth parallel have shown that, as far back as the Archsean, a fault occurred along the range coinciding for the most part with its present western foot. Renewed dislocation on the same jjlane occurred at the close of the Cretaceous or early in the Eocene, again in the Quaternary, and the fault appears to be in progress even at the present day, for so fresh is the most recently exposed surface that vegetation has not had time to clothe it. The observers draw the inference that such fractures in the earth's crust always remain lines of weakness, liable on comparatively slight occasion to further dislocation. During the Trias-Jura the gulf or inland sea, of which the Wahsatch formed the western shore, was shallow in the northern and central portions of Utah, and the sediments consist of sandstones and shales, often cross-bedded by the action of currents. Numerous pools seem also to have been cut off' from the main body of the water, and thus to have been exposed to evaporation. The result is seen in frequent gypsum deposits, which are, for the most part, thickest at the center and thin out toward the edges. Such conditions are not favorable to marine life, and a very large part of the strata representing the Trias-Jura contain only fragments of vegetation from surrounding coasts. At the southern end of the territory during the Jurassic the sea was deep and deposited calcareous sediments. During the Cretaceous the water was for the most part shallow toward the north, and, in consequence of gentle oscillations in level, land and sea frequently alternated on the eastern side of the Wahsatch. Portions of the country, however, were maintained long enough above sea-level to permit of the growth of an extensive flora, and, as a consequence, the Cretaceous strata are marked by the presence of numerous carbonaceous beds, which often contain coal seams of fair thickness. In southern Utah the Cretaceous sea at certain points was deep, but throughout the plateau area most parts of it were shallow. After the post-Cretaceous uplift, and throughout the Tertiary, the region east of the Wahsatch was occupied by grAit fresh-water lakes, the sediments of which toward the north, and especially near the Uintah range, are deposited uncouformably on the Cretaceous. In tkis region they are. also unconformable among themselves, showing that orographical changes took place during their deposition. In southern Utah, however, the Tertiary fresh-water strata appear to show no non-conformity either with one another or with the underlying Cretaceous. It is these fresh-water Tertiaries which have been modeled by modern streams into the fantastic forms characteristic of the bad lands. Several large lakes existed in the Great Basin during this era, and similar conditions prevailed through the Quaternary, modified only in more recent times by slight orographical changes and by greatly increased evaporation. The great Quaternary lake of Utah was Bonneville, the kistory of which has been studied by Mr. G. K. Gilbert. According to that geologist the present dry period in the Great Basin is not the only one which it has experienced. A long remote period of drought, daring which the lake sometimes nearly or quite dried up, was succeeded by a long wet period, in which, however, there was an insufficient supply of water to permit an overflow. Next oame a time so iry that the lake altogether disappeared, and then one, of so much precipitation as to allow of discharge by overflow. This was followed by the present epoch, in which the area of water has been reduced to that of the Great Salt lake and the smaller bodies south of it. (a) The eruptive rocks of western Utah are the same as those of Nevada, and are represented by Arcluvan granites, Mesozoic diorites, diabases, etc., and Tertiary or post-Tertiary audesites, rhyolites, and basalts. According to Mr. Hague, no true trachytes are found among the rocks collected in Utah by the exploration of the fortieth parallel. a Second Annual Report of Ilie I>ircutvr of tlie United Statfn Geological Surrey. 40 PRECIOUS METALS. An interesting series of rooks, locally called syenitic porphyries, has been collected in the West Mountain district, Oquirrh range, by the census expert, which seem to be highly augitic granite-porphyries. As in Nevada, there is an intimate relation between the ore deposits and occurrences of eruptive rocks, the former seldom being found except in the immediate neighborhood of the latter. Metallic ores are rare east of the Wahsatch and in the plateau country, where indeed Tertiary strata occupy much of the surface. In southern Utah, however, the Triassic sandstones carry silver and copper, and especially rich strata of this age form the famous silver reefs near Leeds. To the west of the Wahsatch and along the edge of the high plateau a series of ore deposits is found from one end of the territory to the other, forming a true mineral belt. All of these are associated with Palaeozoic strata, which, however, proves nothing as to the age of the deposits ; indeed, it is known that some of them must be Tertiary or post-Tertiary. It seems extremely probable that these ore deposits owe their existence to the solfataric action accompanying the eruption of massive rocks, and that the points where these reached the surface were determined by the line of disturbance, of which the great Wahsatch fault is the most striking manifestation. At all events, it is a fact that the western edge of the post- Cretaceous uplift is marked in Utah by an immense number of deposits. It has been pointed out on a preceding page that there is a strong analogy between the geological relations of the mineral belt of Utah and those of California. There are ores in the Basin ranges of Utah as well as near the Wahsatch, and particularly in the Oqnirrh mountains, which lie to the west of Utah lake. These are very similar to the deposits in the kindred ranges of Nevada. The prevailing type of the ore deposits in Utah consists of more or less regular bodies of argentiferous lead ores associated with limestone, and usually accompanied by eruptive rocks. The original form of the ore was probably in all such cases galena, which in a majority of instances has yielded to decomposition processes for a long distance from the surface, and is now replaced by carbonate, sulphate, and other secondary minerals. Of such occurrences the Horn Silver mine is an excellent type and an important instance. The deposit worked by this mine lies between a foot wall of dolomitic limestone and a hanging wall of rhyolite. The nature of this lava is proved by microscopic slides in the census collection. Small masses of galena occur, but the prevalent mineral is the sulphate which has formed in consequence of oxidation of the galena. It is a significant fact that heavy spar is one of the gangue minerals, but occurs only near the rhyolite. The same district shows other volcanic rocks. An augite-audesite is found near the Horn Silver inine ; and the Carbonate mine, near by, is associated with a hornblende- andesite of so-called " trachytic" habitus similar to the Mount Eose hornblende-andesite of the Washce district. The veins in Utah which are associated with slates or quartzites do not commonly carry a preponderance of lead ores, but are cupriferous and sometimes auriferous ; the gangue in such cases is also generally quartz. Of such mines the Ontario Is much the most important. The Ontario mine in the Uintah district, Summit county, is a strong vein, several feet wide. Its ores are zincblende, galena, fahlerz, and pyrite, with some horn-silver and copper carbonate in a quartz gangue. The walls are, in the main, quartzite, but at 400 feet a porphyry was struck near the.vein which appears at lower levels in contact with the vein, and it is thought will replace quartzite as the hanging wall. Unfortunately the specimens of this porphyry received are too much decomposed to make determination possible. It is full of pyrite, and has manifestly been subjected to solfataric action. The Ontario is one of the richest mines in the country. Its ore is treated by roasting in a Stetefeldt furnace and amalgamation. The sandstones of southern Utah and the adjoining regions carry a very unusual form of ore deposits, consisting of impregnations of silver and copper, partly native and partly as sulphides. Much of the silver sulphide has also been converted into chloride. The age of these sandstones was determined by Professor J. Marcou, and subsequently by Dr. J. 8. Newberry, as Triassic a determination confirmed by Messrs. Gilbert and Howell. (a) The geological information which has been published on this subject is very largely due to Dr. J. S. Newberry. (b) After having described the peculiar character of the Triassic sea in this portion of the continent and mentioned the well-known facts regarding the silver contents of ordinary sea- water, this geologist states his opinion as to the origin of the silver and copper in the sandstones as follows : Near the Utah shore of this Triassic basin the water would seem fo have been more highly charged than elsewhere with silver, though it was also the associate of the more abundant copper in New Mexico, the Indian territory, and Texas. Doubtless this silver was brought up in springs on the old land from the same sources which furnished so large an amount of silver to the fissure veins formed there long after. Near the old shore the drift-wood brought down by the draining streams and scattered by the shore-waves, when buried in the accumulating sediment, became more or less replaced by copper and silver, precipitated by the reducing action of organic matter which is manifested in so many different ways. The quantity of silver in some of the bays and estuaries carried by draining streams, perhaps fed in part by mineral springs, may have been greater than that in most parts of the water-basin, and hence the sediments formed there hold a quantity larger than the average. We find the same variation in the distribution of copper farther east. In ome places it was so abundant that it was not all taken up by the decaying wood, but formed concretions of sulphide in the sand or , clay. ** , The ores of silver and copper plainly existed as solutions, which saturated the sand when it was collected and deposited the sulphides with sandstone after the mechanical action which transported the sediment was at an end. All this, however, was within the Triassic age, while the water was shallow and highly charged with mineral matters. a Surveys West of the lOQIh Meridian, vol. 2, p. 176. b See especially Engineering and Mining Journal, vol. 31, p. 6. GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 41 He states later in the same article that he regards it as possible, though uot probable, that in some places the porous sandstones of the Trias were penetrated by solutions, from which the sulphides of copper and silver were precipitated. The undisturbed condition of some of the sandstones is certainly an argument in favor of the supposition that the ore was deposited with the sandstone, but there are considerable difficulties involved in its acceptance. Common sea-water will dissolve only an extremely small amount of silver salts, though saturated solutions of salt are capable of dissolving silver chloride in considerable quantities. If the Triassic sea held the silver in solution, it can only have been charged with the metal after isolation from the main ocean and concentration by evaporation ; but it is difficult to suppose this combination of conditions prevailing over wide areas. The deposits of commern in Ehenish Prussia present very strong analogies to those of Silver Keef, but there it is an argentiferous, though otherwise very pure galena, which is disseminated through sandstone. There are strong chemical objections to supposing this galena to have been deposited directly from the ocean, or even from a land-locked basin of concentrated sea- water ; yet a satisfactory theory would give an account of it as well as of the Utah silver. The theory of impregnation of the sandstones by solution presents, in my opinion, fewer difficulties. It is not easy to see why the replacement of organic matter, such as wood, by the metals would not occur as readily from an ascending solution as from sea-water, while ascending solutions would certainly favor the formation of the considerable nodules of ore sometimes found in the sandstone. May these deposits not, after all, be chemically and physically analogous to ordinary veins, though so different from them structurally ? It is supposed that precipitation takes place in veins where there is room for deposition, and where at the same time relief of temperature and pressure or chemical action, especially that of organic matter, induce precipitation. In ordinary rocks such conditions are to be found mainly in fissures, but in sandstones, particularly such as carry organic matter, they may occur anywhere, and the presence of copper or lead would be as readily accounted for as that of silver. Dr. Newberry records that analyses made at his instance by Mr. J. B. Mackintosh shoflfcthat the silver in some of the sandstones is accompanied by selenium in considerable quantities. The number of workable coal-seams in Utah is very considerable. Those thus far opened lie for the most part on the eastern flank of the Wahsatch, or not far from the western edge of the high plateau, and while search for them elsewhere is by no means hopeless, these localities seem most likely to show good seams. Both Cretaceous and Tertiary beds are said to occur, (a) and some of them are reported to present very unusual qualities for coals of such recent date, not crumbling on exposure, containing a very small amount of water, and yielding strong coke. The great value of such beds, at an immense distance from the well-explored coal-fields of the Carboniferous era, is patent. In the appendix will be found a report on the mining industries of Utah by Mr. D. B. Huntley, who filled the office of special expert for the territory. This paper describes the mineral resources in so much detail that any special notes ou the counties are unnecessary here. BEA.VEK. . DeterminatioBS in parentheses are given on the authority of the experts.] WAL LS. Character of Foot Hanging. deposit. BRADflHAW. Irregular bodies. 8AN FRANCISCO. aragonite, and limonite, (manganese oxide, native sulphur). Rhyolite * Chimney. noysito, prouslite, (pyrarjiyrite). oerarjryrite, argen- tito also occur with calcite, quartz, and buiite. Hornblende-andeaite * Vein. Irregular bodie*. Limestone and slate Pipe*. STAB. fluorspar). Black limestone. Dolomitic limestone Chimney. Siliceous limestone. Kebel Galena cerussite free sulphur, gypsum, and quartz, Crystalline limestone Crystalline limestone. (limonito). Granite * Dolomitic limestone Chimney* silver). Microscopically examined. a E. E. Howell in Surveys West of the IWth Meridian, vol. 3, p. 278. 42 PRECIOUS METALS. (NOTE. Determinations in parentheses are given n the authority of the experts.] Mine. Ore and gangue. WALL*. Character of deposit. Foot Hanging. TDiTlO. (Porphyry) (Porphyry) Pipes. Mineral bolt. Vein. Do. Irregular massed. Vein. Vein. Vein. Do. Do. British (Copper minerals, limonito, calcito, quartz, rarely gold, and manganese oxide.) Quartzose, carrying limonito and lead, probably as cerussit*, (copper carbonates and sulphides). Erubescito, auglesito, pyrito, mispickel, quartz, (lim- ouite). Galena nnd its decomposition products, copper stains, hematite, quartz, calcito, (lead ocher, gold, horn-sil- ver, auil zincbleudf). Bismnthite (argentiferous). Siliceous and ferruginous rock (carries bismuth and silver). Ferruginous quartz, calcite, and cenissite (?) Carisa 3'robably dacito, * (lime- atone). Hornblende-andesite* Probably dacite, * (lime- stone). norublende-audesite * Eureka Hill Siliccoua limestone Indetcrminably decomposed massive rock. Andesite, (?) decomposed and pyritiferous. Siliceous limestonn Indetertninably decomposed massive rock. Andosito, (?) decomposed and pyritiferous. Golden Bell Cuprite, pyromorphite, copper carbonates, quartz, cal- cite, pyrolusite, (liinouite, argentite, and horn-sil- ver). Limestone. Diorito* Anglesite, iron oxide, and quartz. Galena, ceruasite, qnartz, (limonite and silver, prob- ably as argentite). Argentiferous pyrolusite, (galena, gold, and copper) . . . Galena, cernssite, calcite, and quartz. Diorite* Park Rising Sun . (Granite) (?) (Granite) (?) * Microscopically examined. PIUTE. [NOTE. Determinations in parentheses are given on the authority of the experts.] OHIO. Bullv Bov Vein MOUNT BALDY. Beer Trail hedrite, chnJcopyrke, chalcosite, aad quartz). Qunrtzite Green-Eyed Monster feuite, quartz, (lead ochor and copper sulphides). do .... do do Do Pluto * Microscopically examined. SALT LAKE. [NOTB. Determinations in parentheses are given on the authority of the experts.] BIO COTTON-WOOD. Anellie Melaconite and malachite, (lead, silver, and gold) . Gulena, limonite, copper stains, and calcite, (cerussite and manganese oxide). Galena, limonite, calcite, pyrolusite, and quartz (Limestone). Limestone. do Vein. Bedded vein. Bedded vein. Vein. Belt. Vein. Vein. Vein or belt Antelope & Prince of Wales. Butto do Carbonate Galena, ceruasite, limonite, and calcite Galena, cerussite, malachite, pyrite, quartz, calcito, talc, (manganese oxide and lituonite). Galena, cerussite, copper stains, pyrolusite, nnd iron oxide. Cerussite, plumbic ochcr, auglesite. and tuilcite Galena, cerussite, plumbic ocher, (copper stains, quartz, and limouite). (Galena, ceruaaite, limouite, and quartz) (Galena), corussite, angleaite, and pyrolaaite. (Galena), cerussite, wnlfenito, cuprite, malachite, py- rolusite, and limonite. Galeua and quartz. Galena, cerusaite, anglesito, limonite, calcareous gaugue, (manganese minerals). Galena, dufrenoysite, pyrite, calcareous gangue, (tet- rahedrite, zlncblende, and qnartz). (Galena and cerusaite) Dolomitic limestone. Maxfleld Ophir Blue limestone. Limestone. Keed & P>enson : Silver Mountain Thor & Bright Point Quartette Limeatone and diorito * .... LITTLE COTTOXWOOll. Cincinnati Limestone and diorite. * City Kocks Dexter Emma Emily Equitable (Limestone). (Limestone and sandstone). Limestone. Evergreen (Galena, cerussite, limonite, and copper carbonates).. Cernsaite, copper stains, limonite, and manganese minerals. (Limestone and sandstone) . . Grizzly Louise North Star Galena, cernasite, and wnlfenite ... Limestone ... Limestone . . GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 43 SALT LAKE Continued. Mine. Ore and gangue. WALLS. Character of deposit. Foot. Hanging. UTTLE COTTOXWOOD COnt'd. Galena, cernssito, plumbic ocher, wad, enargite, py- rite, rhaleopyrite, malachite, nian-iwite, calcareous gangue, (oxide of manganese and quartz). (Quartzite) (Qnartzite) Vein. Vein. Vein. Vein. Belt. Vein. Bedded vein. (?) Vein. Bedded vein. Belt Do. Vein. Bedded vein. Vein. Vallejo Galena, corussito, aniilt-site, copper stains, limonito, ban. s man u iU-, and wuliV-nite. Cerussite, limonito, probably horn-silver. Galena, /incblende, copper pyrite, (limonite, silver, and gold). Dolomite. (Black limestone) WEST IfOUXTAIS. Highland Boy Qnartzite Limestone. Siliceous limestone Galena, (gold), iron and copper pyrites, cernssite, limo- nite, quartz, and copper stains. do Granite-porphyry* Granite-porphyry. ' (Between granite and quartz- ito.) (Quartzite). Qnartzite Orpiment and realgar. (Between granite and quartz- ito.) Galena, reniasito, iron and copper pyitftes, malachite, limonite, nud quartz. Galena, cernssite, argent ito t pyrar^vrite, rhodocrosite, zincblendo, quartz, bartte, (Dornlte, culuite). do Aujritic granite por- phyry. (!)* Anuitic granite por- phyry. (?)* Qnartzite Stewart No. 2 Gold, quartz, limonite, (silver and copper carbonate).. (Unknown) ....do /OimrtiitRl Quartzite - Quartzito Galena, binnite, zincblende, pyrite, cerussite, quartz, iron oxides, (ruby silver and native silver). Victor (Quartzite) (Onartzite) Galena, dufrenoysite, iron and copper pyrites, cerns- site, limonite, zinc-vitriol efflorescence, native sul- phur, (zincblende, cubanite, tetruhedrite, calcite, and gypsum). Galena, cerussite, iron and copper pyrites, mel&conite, limonite, (boruite, zincblendo, and quartz). Shale Quartzite * Microscopically examined. SUMMIT. [Nora. Determinations in parentheses are given on the authority of the experts.] UIKTAH. Qnartzite (Said to be porphyry) Vein. nese oxide, and liiuonite. (Qnartzite) (Qnartzite). Qnartzite Qnartzite and indetermina- Vein. White Pine 1 bleude, (pyrite), horn-silver, malachite, clay, (quartz). ble dioi ite-like porphyry. Diabase (!) Do. Walker & Webster rahedrite, argeutite, 'and native silver). Galena, cerussite, and quartz. (Green porphyry) . Vein. Woodside bonate, manganese oxide, limonite, and quartz.) (Cerussite angleaite galena, iron oxide, and calcite) (Qnartzite) (Siliceous limestone) Vein, (t) TOOELZ. [UTOTB. Determinations in parentheses are given on the authority cf the experts.] CAMPFLOTD. Carrie Steele Stibnite quartz limonite, (horn-silver and antimonial Limestone Siliceous limestone Bedded vein. OFHIR. silver). (Limestone) Bedded vein. ...do ....do Bedded mass. g do .... do Vein. . ' ^ Limestone, quartz-porphyry Slate dike Chimneys. Sandstone Irregular bodies. native silver, horn-silver, aud limouite.) Limestone and qnartzite .... Indeterminable porphyry Bedded vein. Galena, cerussite, plattnerite, (?) pyrite, (horn-silver, (Clay shale, close to lime- (Clay shale, close to lime- Vein. chalcopyrite, and limouite). stone.) Fetid limestone stone. ) Calcareous sandstone o. and ealcite. Cernssite, limoait<', and calcic, (the limonite is argen- Limestone Limestone Do. tiferous). do do Pipes. RUSH VALLEY. First National Galena, < f, liinoirit\ ; . :;ud (SilH-i-oiis limestone) (Black limestone) Bedded vein Great liasln CcnmMte, limonite, clay, (argentiferous galenn, mala- Limestone . chite, aud manganese minerals). Limestone 44 PRECIOUS METALS UTAH. [NOTS. Determinations in parentheses are given on the authority of the experts.] Mine. Ore anil gangue. WALLS. Character of deposits. Foot. Hanging. AMKBICAX F01IK. Galena, pyrito, qnartz, (silver, gold, zinculcndo, and copper ore). Galena, ccrussite, zincblende, pyrite, limonito, (silver, gold, aud quartz). (Galena, cerussite, limonite, and clay) (Quartzite) (Quartzite) Veto. Do. Do. Do. Do. Pipe*. Pocket*. Miller Shale (Limestone) "Wild Dutchman Galena, cerussite, zincblendo, quartz, luuonite, arsen- ical and autiuionial compounds. (Cernssito, pyrite, quartz, Hmonite, and copper stains.) Galena, cerussite, quartz, limonite, (pyrito and zino- blende). Limestone ....do Limestone ....do SILVER LAKE. Milkmaid Quartzite (Quartzite) WAnsATcn. [NOTE. Determinations in parentheses are given on the authority of the experts.] BLUE LEDGE. Granite * Vein Wahaatch . (Quartzite) (Quartzite) Do. SNAKE CREEK. Malachite, limonite, calcito, and (qnartz) Granite* Granite* Vein. Shale m Utah . Galena, cerussite, zincblende, pyrite, clay and (tet- Quartzite Vein. raliedrite). * Microscopically examined. WASHINGTON. [NOTE. Determinations in parentheses are given on the authority of the experts.] HABKI8DURO. Magnesian clay, showing flakes of silver. Sandstone Bed. Barbee & Walker with native silver aud argvutite. Fossil plants re- placed in part by silver and horn-silver. Sandstono with native silver and sulphurets, (horn- Sandstone Do. Duffln silver, argentitc, aud lignite). do do Do. live silver). do do Do. Leeds (silver, argciitite, and lignite). do do Do. Maud etable matter.) do do do Do. Stormont do '...do .. do .. Do. GEOLOGICAL SKETCH OP ARIZONA. In the latitude of Salt Lake the Cordilleras, as Humboldt called the entire system of western .North American mountains, occupy a breadth of over 1,000 miles. In the latitude of Tucson they are contracted to about half this width, which is still further reduced in Mexico. While Nevada occupies only a portion of the breadth of the Great Basin, Arizona, though no wider, includes a large part of the plateau region, the southern continuation of the Basin ranges, and probably a portion of the group of ranges of which those on the southern coast of California are members. The topography is thus extremely diversified and for the most part mountainous. There are fertile valleys and well- wooded mountains in the territory, but the prevalent character is one of great aridity, and in the southwestern portion there are large tracts of shifting sands, relieved only by occasional cactuses, in comparison with which the sage-brush plains of the Great Basin seem areas of luxuriant vegetation. Arizona is, of course, famous for its mines, which produce chiefly gold and silver, though lead and copper, particularly the former, are rather abundant, and will, no doubt, be exploited on a large scale when the railroad system is further developed. Coal also occurs in considerable quantities. A number of geologists have visited Arizona. Dr. Newberry was a member of Lieutenant Ivel's expedition in 1857 ; Major Powell and Captain Button have explored the Colorado cafion and a portion of the plateaus, and the geologists of Captain Wheeler's survey have contributed very greatly to a knowledge of the main features of the territory. But little detailed work, however, has been done in the mining regions, aud such of the facts ascertained as are appropriate to this sketch are soon told. GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 45 Northeastern Arizona belongs to the Colorado plateau, of which about one- third falls within the limits of the territory. The Arizona plateaus arc for the most part nearly level, though, as in Utah, there are folds, and even ranges, of uplifted mountains at long intervals. The southwestern limit of the plateaus is roughly indicated by a straight line running northwest from a point in latitude 33 30', longitude 110. T- tlie, cast of this imint the limiting line curves eastward, and in the adjoining territory of Xcw Mexico turns toward the north. The plateau country separates two systems of ranges which meet to the south of it. Of these the eastern group have a northern trend and pass into the Rocky mountains 46 PRECIOUS METALS. of Colorado. The western group trends northwest, and is continuous with the Basin ranges of Nevada. Only the latter ranges are met in Arizona, the most westerly of those of northern trend occurring in New Mexico just easfc of the dividing line. The region in which the plateaus and the two systems of ranges meet is characterized by an immense lava field covering between 20,000 and 25,000 square miles. The relations of the two systems of ranges to the plateau country and the lava fields are shown in the sketch map on page 45, borrowed by his permission from Mr. Gilbert's report on the geology of parts of Arizona and New Mexico, to which our knowledge of the region in question is chiefly due. Concerning southwestern Arizona there is extremely little definite information. This portion of the territory is mostly composed of granites and crystalline schists, and the mountain ranges are somewhat irregular. They appear, however, to belong to the same structural system as those of California south of fort Tejon, with which they conespond in a variety of details. In Utah the edge of the plateau System is nearly coincident with that of the inland Cretaceous sea. In Arizona this is by no means the case, the surface of a great part of these elevated plains toward the west being of Carboniferous age, and the Triassic being largely represented on the surface. The belt of Palajozoie included in the plateau country, measured from the southwestern edge of the latter, averages about 80 miles in width. The ranges trending northwest and continuous with those of the Great Basin are also composed of Palaeozoic strata, except where the Archaean is exposed or where volcanic rocks hide the sedimentary beds. Captain Button's investigations have established that the Jura-Trias strata formerly reached the edge of the plateau system in Arizona as they did in Utah, but have since been removed by erosion. This is .shown by the presence of remnants of these beds protected by lava near the edge of the plateau, and by the impossibility of reconstructing their surface, except on the supposition that they reached this line. The elevation of the range system, judging from the analogy of the Great Basin, is most likely referable to the post-Jurassic disturbance which resulted in the formation of the Sierra Nevada. Whether the Jura-Trias beds were also raised above water-level along this line at this time is uncertain, but it would not be surprising if this should prove to be the case. The Cretaceous sea in Utah was shallow, and a slight post- J urassic elevation would have thrown its shore far east of the Wahsatch. Such a change of shore line may have taken place iu Arizona and left the western portion of the plateau dry, or the shore line may have been nearly coincident with the edge of the plateau, aud the Cretaceous deposits afterward removed by erosion, like those of the Jura-Trias. The disturbance to which the Arizona ranges is due extended eastward to the edge of the plateau country, and the post-Cretaceous upheaval which raised the plateaus extended westward to the ranges, exactly as was the case in Utah. Iu the northern part of the territory the contact between the Palaeozoic area aud the crystalline rocks to the southwest of it has been traced for a long distance. This line probably lies somewhat to the northeast of the original edge of the Palaeozoic, but at no great distance from it. That a portion of these strata have been removed by erosion is indicated by the occurrence of isolated patches near the main area. The most remote of these is reported as occurring in the Bill Williams Park country, aud may represent a gulf in the Palaeozoic sea. Though the southwestern portion of the territory has not been systematically explored, it has been traversed in many directions by geologists who would not have failed to recognize Palaeozoic strata had they encountered them, and it is probable that they are absent from that region. The main contact between the Palaeozoic aud the underlying strata is laid down in the geological maps of th surveys west of the 100th meridian continuously from Virgin canon to Camp Verde, a distance of 170 miles. Farther south the most westerly occurrences of Palaeozoic shown are im the Pinal mining district near Florence and in latitude 32 20', longitude 100 40'. These are probably near the edge of the area, though there is some evidence of detached patches still farther to the south, and to the west of the general course of the contact so far as traced. The Chiricahui range Las been shown by Mr. Gilbert to be largely made up of Palaeozoic strata, aud the mines of the Tombstone district are many of them sunk on deposits in limestone. In this region limestones can hardly be other than Paleozoic, aud they are reported as containing Carboniferous fossils. The rocks adjoining the Palaeozoic to the southwest are unquestionably Archaean, for their relations to the Silurian are clear at a great number of points, and their lithological character in this region is very characteristic and persistent. There seems no evidence that these Archaean rocks have been covered at any time, except where comparatively small patches of the Palaeozoic have been removed by erosion near the contact. Had this area formed a sea bottom, like the corresponding region to the north, during the Trias-Jura, it is scarcely supposable that the thick sediments which must have formed should have disappeared without traces which would have been detected before now; aud while ouly an elaborate field study can establish the facts, it seems allowable to suggest the probability that the subsidence of the Archaean, which took place at the close of the Carboniferous in western Nevada, did not extend to central Arizona, so that the continental area of the Trias-Jura embraced eastern Nevada, western Utah, and most of Arizona, excepting the northeastern corner. The Pacific coast ol that time followed the meridian of 117 30' (approximately) to the neighborhood of Owen's lake. If the supposition stated above is correct, it must then have left the Palaeozoic area and continued in a southerly or southwesterly direction. It appears most probable, on the whole, that it passed to the south of fort Tejon and out into the area at present covered by the Pacific. The coast in San Bernardino county, California, has no doubt slowly changed its elevation repeatedly, but GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 47 Professor Whitney states that, while in that county a belt of 10 or 12 miles next the coast is occupied by Cretaceous and Tertiary strata, the region back of this is composed of granite and highly crystalline rocks of the geological age, of which nothing is known, (a) Such descriptions of San Bernardino county as have been published, however, show that the rocks are extremely similar to the Archsan of Arizona, and in the absence of definite information it may be assumed that they are identical. If so, there is a body of Archaean reaching from San Diego to Camp Verde, a distance of about 300 miles. Its northern limit is not far from Owen's lake, ami its southern extension is unknown. If the shore line of the Pacific ocean in the Mesozoic era passed westward or southwestward from near fort Tejon to the present coast, Jura-Trias strata probably underlie the coast ranges in that neighborhood, and it is possible that they may somewhere be exposed. It is, of course, wholly impossible to assign a date to the Archaean ranges of Arizona, the more so that the topographical maps of the area are very inaccurate. These mountains scarcely appear to form a portion of the Basin range system, but they may have been raised at the same time, for, though their lithological character differs greatly from that which prevails in those ranges, the trend and general relations of the Archaean mountains certainly do not diifer more from those of the Palaeozoic ranges of Arizona than the Mesozoic Sierra Nevada from the ranges of the same era in western Nevada. It at least seems more likely that the Archaean ranges date from the post- Jurassic upheaval than from cither of the three other important uplifts mentioned, while it scarcely seems possible that any traces of a pre-Palteozoic mountain formation should have withstood erosion till the present day unless protected by overlying rocks of later age. Of the eruptive rocks of Arizona not much is known. Besides granite, there are enormous quantities of true basalt and of other volcanic rocks which have not yet been subjected to the minute examination necessary to classify them satisfactorily. The census collection contains numerous specimens of pre-Tertiary eruptive rocks, quartz- porphyry, diabase, and diorite. If the analogy of Nevada could be trusted, these rocks would be regarded as Mesozoic, aud as probably post- Jurassic. They appear in the Palaeozoic ranges, not merely as dikes, but as lai\;e masses, inclosing veins, and their extrusion was most likely a concomitant of the disturbance to which the formation of the ranges is due. Though only an examination in the field can determine the age of those mountains, the occurrence of ttiese eruptives is another argument for referring them to the great Mesozoic upheaval. The census collection of the Pacific division contains only a single syenite. This forms the hanging wall of the Golden Eagle mine, Globe district, Pinal county, Arizona territory. A slide shows orthoelase, a little plagioclase, hornblende, mica^ and scarcely a trace of quartz. The exploration of the fortieth parallel encountered but one syenite. This was found in the Cluro hills, Cortez range, Nevada, and contains much more quartz than that from the Golden Eagle mine. The latter, however, bears a strong resemblance to the granite which is the prevailing rock in the Globe district, and is represented in the census collection by a large number of specimens. The Cluro Hills syenite is also scarcely distinguishable from the granite of the same region, and it may fairly be asked whether both are not to be considered as granites containing an unusually small proportion of quartz. As is well known, almost every fresh investigation of European syenites diminishes the number of occurrences to which the name is ousidered applicable, and it seems not unlikely that it will eventually disappear from the list of rocks. The ore deposits of Arizona in a majority of cases are found in connection with massive rocks. Often both walls are granite or some later eruptive; in many cases a massive rock forms one wall of the veins, and even where limestone or shale entirely inclose the ore it is known in some cases that eruptive rocks occur close in the neighborhood. The relations of the mineral belt as a whole to the southwestern edge of the area of post- Carboniferous upheaval have already been sufficiently commented on. AFAC1IK COUNTY. In the northern part of this county good coal seams exist in the Cretaceous, but at present they are little exploited for want of facilities for transportation. At the southern end of the county, where it adjoins Pima, cupper ores, with blende and pyrite, occur in the veins associated with limestone and quartzporpbyry. There are also gold placer mines in the same neighborhood, and consequently there must be gold quartz veins, though none such have been reported by the experts. APACHE. WAI ItM. Character of Foot. Hanging. deposit. COPPER MOUNTAIN. Melaconite and azurito, zincblende, pjrite, with cal- l.KI.KXLEE GOLD MOUNTAIN. careous gangue. Probably diorite . . ... Placer. Quartz-porphyry. a Auriferous Gravel*, \). If. 48 PRECIOUS METALS. MARICOPA COUNTY. Maricopa county includes a portion of the plateau country, and extends across the range system far into the Archteau area. The principal mining district in this county is the Globe, about half of which, however, lies in Final county. The principal ores are argentite and cupriferous minerals, associated with galena and zincblende. The ordinary gangue mineral is quartz, but heavy spar also occurs. The inclosing rocks are usually granite or highly metamorphosed strata, but the walls of the Mexican mine appear to be diabase. This district is nearly on the contact between the Palaeozoic and the Archaean. MAEICOPA. [NOTH. Determinations in parentheses are given on the authority of the experts.] WAI very large, and contains a number of mineral neighborhoods. At Chloride veins occur in granite with quart/ gaugue. Xcar thesurface the ore minerals are carbonate of lead and silver chloride. Below the water level these are replaced by galena and pyrite. The mines mentioned are : Schenectady, Schuylkill, Empire, Juno, Silver Hill, Pinkeye, Kanawha Belle, Oriental, and Porter. Xear Stockton deposits are found which are similar to the foregoing, but they are reported as containing also native silver and ruby silver, as well as ziucblende, chalcopyrite, and some stibnite. The mines mentioned are: Indian Boy, I. X. L., Tiger, Ed. Everett, Cupel, Dolly V., Pure Metal, Little Chief, Prince Geo., and Tigress. At Mineral Park native silver and silver chloride occur near the croppings of the veins which carry a quartz gangue and are inclosed in granite. The undecomposed minerals are argentite, ruby silver, stephauite, with some galena and zincblende, iron pyrite, and arsenical pyrite. The mines mentioned are: Keystone, Lone Star, Fairfield, Quick Relief, Conner, and Metallic Accident. At 'Cerbat the ore thus far mined carries horn-silver in a quartz gangue, with some native gold and silyer, complex sulpharseuides, and antimonides and /incblende. The mines mentioned are : Cerbat, Black-and-Tan, Suowflake, Mocking Bird, Sixty-Three, Falstaff, Fonteuoy, Champion, New London, Flora, and Paymaster. The Maynard district, like the Hualapai, shows quartz veins in granite and mineral associations similar to that last mentioned. The mines reported are : The American Flag, Peabody, Dean, Antelope, and Mississippi. The Cedar Valley district is also in a granite country. The ores are argentiferous galena, ruby silver, tetrahedrite, and, near the croppings, horn-silver, accompanied by zincbleude, pyrite, and quartz. The mines mentioned are: Silver Queen, Hibernia, Hope, 'General Lee, Arnold, Hilly Eugle, Eainbow, Eugenie, Bunker Hill, Congress, and Gunsight. Owens district is in a granite country, but a portion of the rock is gneissoid. The ores are argentiferous galena and argentite, with decomposition products near the croppiugs and a quartz gangue. The mines of the McCracken company and the Signal mine are the chief ones of the district. PIMA COKNTY. This county occupies the southern end of the territory, and crosses the mineral belt. It contains a very large number of districts, the most famous of which is Tombstone. Many of the mines in this district are in limestone, and carry chiefly argentiferous lead ores. Manganese minerals (pyrolusite and wad) sometimes accompany them, in large quantities. There are also veins in the Tombstone district in quartzite. These carry cupriferous minerals more or less charged with silver and some free gold. From mine reports and papers by Professor W. P. Blake it appears that the ore in the Tombstone district occurs in Paleozoic beds, probably of Carboniferous age, which have a prevailing inclination to the north and east, resting on a granitic base, which outcrops some distance to the southwest. These beds consist of a tine- grained qnart/ite, called by him novaculite, about 140 feet in thickness, underlaid by a light-colored dolomitic limestone and overlaid by a blue-black limestone passing into shaly beds. The principal portion of the ore is found at the horizon of this blue-black limestone. The sedimentary formations have been compressed into a series of sharp folds and fissured and traversed by dikes of pre-Tertiary eruptive rock, known in the district as diorite. The census collection from Tombstone contains both diorites and diabases. The general direction of the fissures and dikes lies between north and northeast. The ore occurs both in fissures which cross the strata either parallel to or in direct connection with the dikes and in bodies branching out from these approximately vertical bodies in a more horizontal direction, following in general the bedding planes of the formation, whose prevailing dip is to the northeast. The ore is most abundant and richest in that part of the black limestone beds which are contiguous to the quartzite, and the vertical fissures generally contract and become less rich where they cross the quartzite itself. Their continuation in the lower limestone beds has not yet been much explored. In the origin and manner of deposition of its ore bodies the district would seem to resemble that of Chauarcillo in Chili. There are also veins in the granite, or associated with it. near Tombstone, which are similar to the other deposits of the territory found in this rock. The group of districts, including the Oro Blanco, Arivaca, Harshaw, etc., just north of the Mexican line, seem to possess much the same character as Tombstone. The country rock- is granite, limestone, quartzite, or earlier eruptive rocks, and the ores are galena and its products of decomposition, ordinarily accompanied by copper minerals and charged with silver. They are sometimes auriferous. In the western part of the county there are gold and copper mines, with some lead ores. These are sunk on veins in granite, which carry, besides quartz, tiuorite and heavy spar as gangue minerals. VOL 18 4 50 PRECIOUS METALS. rniA. [NOTE. Determinations ill parentheses arc jjiveu c,n (lie itiithority of the experts.] Mine. Ore and gaugue. WALLS. Character of deposit. Foot. Hanging. AlilVAl-A. Copprrstaius and black sulplmrets in small quant ities, with quartz and barite, (also chlorides aiid carbon- ates). The ore shows blue stains, which are possibly horn- sUver. (free gold and horn-fliiver),jailffue quart /.and Uroonite. (Fre<- gold and horn-silver), gangue quart/- and limo- uite. Vein. Vein. Do. Pockets. Do. Vein. Do. Do. Vein Vein. Do. Do. " Flat." Vein. Vein. Connected poekets Connected pockets. Do. Connected pockets. Do. Do. Do. Do. Veto. Do. Do. Do. Probably vein. Vein. Pocket*. Vein. Do. Do. Do. Pockets. Vein. 1 Vein. Probably vein. liOS CAHICZAS. Shale Shale (Slate) IIAKSHAW. Quartzite. Limestone Ceiua.site and 0 miles west of that boundary. For a shoit distance from the junction the course of the river is nearly south, but it bends gradually westward and northward, reaching the Oregon line on a northwest course. The area south of the Snake river is about one-fourth of the entire territory. The valley of the Snake is a plain from 50 to 1(10 miles in width, which is occupied by a vast sheet of recent basalt from the Wyoming line to Owyhee county. Immediately to the north of this plain, which has an elevation of a little over 4,000 feet, the character of the country changes abruptly, and most of the rest of the territory is extremely mountainous, many of the suirimits rising to between 10,000 and 12,000 feet above sea-level. The climate changes with the topography. Central and northern Idaho are east of Oregon and Washington territory, to the coasts of which the trade-winds of the Pacific bring an enormous amount of rain. The coast is, indeed, separated from the northern portion of the Great Basin by the Cascade range, but this is much lower and much less continuous than the Sierra Nevada to the south. The westerly winds thus bring a greater amount of moisture to northern Idaho than to Nevada, while, the lofty peaks of the northern area promote its precipitation. To the. north of the Snake River region Idaho is consequently well watered and well wooded, conditions of the utmost importance to profitable mining. On the other hand, the winters are long and severe, and lines of communication are extremely circuitous. Except in the eastern counties, no portion of Idaho has been submitted to systematic geographical or geological survey, and the maps of the territory are very inaccurate. The geologic.) 1 information furnished by the census examination is necessarily fragmentary, presenting only data from a large number of mining localities, and but little assistance can be derived from any local publications with which I am acquainted. The following paragraphs, therefore, contain only a very rude outline of the geological conditions of the mining regions of Idaho. A very large giauite area occupies a portion of southwestern Idaho. It appears to be oval in shape, its longer diameter extending from a few miles south of Yankee fork nearly to the South Mountain district, while its shinier diameter reaches from the common boundary of Washington and Boise counties in a southeastern direction to the Wood River country. Its total area is probably about 12,000 square miles. Not all of the country within this oval area shows granite on the surface, for Ada county is largely alluvium, and Palaeozoic limestones are reported as occupying much of the more northern portions; but the extremely frequent occurrence of granite, for the most part of a single type, appears to justify the supposition that the body is continuous under the later formations. The granite from the Idlewild mine, Carson district (Silver City), Owyhee county, i < a soft gray rock with rather well developed crystals of white mica, cleavage flakes of which give the biaxial interference, figure of muscovito. Slides show undei the microscope that llu- constituents are orthoclase, oligoclase. quartz, and mica, with a little GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 53 apatite and magnetite. The quart/, is extremely full of fluid inclusions, many of them containing moving bubbles. The sti iicturo is the ordinary one of granite ; indeed, the rock is quite typical. In the same district occur excellent quart/ porphyries, slides of which show dihexahedral quartz crystals, with the characteristic association of glass and fluid inclusions. The association of these two rocks suggests a similar origin, or, in other words, that the granite may be eruptive, but of course proves nothing. On the other hand, there is no known evidence tending to show ;t derivation of the granite from sedimentary rocks. The granite from the Sub Rosa mine, in the Boise basin, is in most respects similar to that from Carson district, though about 80 miles distant from it, but contains biotite in addition to the muscovite. In several localities in the territory the granite is extremely coarse-grained, and has even furnished marketable mica sheets. The granite has been profoundly disturbed by eruptive action, aud probably at a comparatively recent date. The evidence of this is manifold. Dikes of eruptive rock, among which the principal one appears to be basalt, (a) are common in the granite, and as basalt appears everywhere to be the youngest of the lavas this would indicate comparatively recent action. Hot springs, too, are thickly distributed through the granite area, in many cases issuing directly from the granite, though usually within a mile or two of known occurrences of volcanic rocks. This is most naturally accounted for by supposing that there are still remnants of volcanic heat at great depths below the surface. A further and most interesting point bearing upon the structural geology of the region and the age of the disturbances is the fact that the very numerous veins found in the granite usually strike in the direction of the ranges on the flanks of which they occur. The fissures which these veins occupy must have been formed by an upheaval such as would produce these ranges, and it seems necessarily to follow that the mountains are substantially a result of upheaval, and not of erosion. ThFs upheaval, too, must be comparatively recent in a geological sense, say as late as the Tertiary, since otherwise the results of upheaval would have been obscured by subsequent erosion. The occurrence of the immense lava fields of the Snake River valley immediately adjoining the granite area suggests that the dynamical disturbances and the thermal action manifested in the granite may be a portion of the same series of phenomena to which the Snake river eruptions are due. The age of the veins themselves is quite another matter. The facts mentioned indicate a possibility that the ores have been deposited alter the upheaval which determined the present topographical character of the country ; it may be through the agency of the solfataric action (b) accompanying the basalt eruption. Indeed, the numerous hot springs of the granite area are in many cases highly charged with alkalies aud sulphhydric acid; in short, they are solfataras. They often occur in the immediate neighborhood of the mines, one of the mining districts in the Wood River country even bearing the name of the Hot Springs district. In a mineral region solfataras, active or extinct, are usually associated with ore deposits, which are commonly ascribed to their action, and it is difficult to see lu>w the period of solfataric activity now drawing to a close can have failed to give rise to metalliferous concentrations in Idaho. On the other hand, the structure of the conulry is not incompatible with the supposition that the veins are far older than the basalt and a concomitant of a former disturbance of the granite. Fissures in the earth's crust, once formed, seem never to heal, aud faults have occurred at the present day on surfaces upon which movements are known to have taken place in the Palaeozoic era. The recent upheavals may merely have followed old lines of movement which had been marked by veins long before the present mountains rose. An indication tending to such a view is the fact that some veins are faulted, though this is not the rule, while slickeusides, showing relat:'~e motion of the walls of the veins subsequent to the deposition of ore, are very abundant. While known movements of a more recent date than the ore deposits are thus shown, the extent of these movements usually appears to be small. Much the strongest evidence of older veins is furnished by the placers of Boise basin and the canon of Moore's creek, a little below and south of the basin. There is, of course, every reason to suppose that auriferous gravels are accumulations from the croppiugs of veins. They do not represent the whole material eroded from a country, but only the heavier portion which the streams have been unable to carry to great distances. The gravels of Boise basin are estimated to cover .">( square miles to an average depth of about 12 feet. This large mass represents not merely a very extensive erosion of the upper country, but streams of a size inconsistent with the present rainfall of the territory. It does not follow, however, that the general character of the topography of the country must have been altered by this erosion to such an extent as to obscure the relation of the strike of the veins ro the trend of the ranges. Not only were these gravels deposited when the climate was much inoister, but they date from a time prior to some of the basalt eruptions, for in Moore's creek, the outlet of the Boise basin, the grave], which is continuous with the main deposit, is covered by a basalt cap which can scarcely be younger than the Snake River bed. In the light of the present knowledge of the country, it seems on the whole most probable that the greater part of the quartz veins of this region are of Cretaceous or possibly Tertiary age, but it is by no means unlikely that a part of them are subsequent to the basalt, and thus are of very recent date. Should this be established by future investigations, it would afford a remarkable instance of the repetition of certain chemical and physical conditions at considerable intervals in geological history. n As tilt' enrjitiv- rocks ;irc not immeiliiitely .-tssoehited with the ore deposits in any of the mines visited, specimens <(' this l>:jsa!t were not collected. b See note to page- ti. 54 PRECIOUS METALS. A very large portion of the mines in Idaho are within the granite district, and are sunk upon veins between granite walls. These veins are very similar to those in the other granitic mining districts of the Great Basin. They are numerous and rich, but narrow, being seldom above 3 feet in thickness, though there are a few wide veins, as, for example, the Atlanta, Middle Boise district, Alturas county, which is from 50 to 75 feet across. The gangue of the veins in the granite area is quartz, accompanied by more or less decomposed granite as horse matter. The ores carry both gold and silver in very varying proportions. The gold is either free or is mechanically entangled in pyrite, mispickel, or zincblende, while the silver appears near the surface as chloride, ; ml at lower levels as sulphide, stephanite, tetrahedrite, or as ruby silver. Zincblende appears occasionally, and galena still more rarely. In some veins gold greatly predominates, in others silver; yet the association of minerals is the same in both classes, the relative quantities only of the two precious metals varying. There is nothing to show that the two classes of veins are of different origin or age; on the contrary, every gradation between the two extremes occurs, and sometimes both are represented in the same vein. On the Atlanta lode the Buffalo and Monarch mines produce about twice as much silver as gold, while in the Yuba tunnel, more than a mile distant from the others, but on the same lode, the value of the ore is almost wholly in gold. From a geological point of view there is little to note concerning the variations of the ore deposits of the granitic area without going into more detail than this chapter is designed to record. On the contrary, the most striking point connected with this area is the great similarity from one end to the other of the inclosing rock and .the included deposits. As soon as the water-line is passed suites of specimens from the various mines are almost indistinguishable, except in point of richness. In prospecting for these veins it would be well to observe not only the float, the character of the croppings. and the like, but also evidences of disturbance, and particularly decomposition of the country rock, for both of these phenomena are likely, though not certain, to accompany the presence of ore. The uniformity in character of the veins throughout the granite area of Idaho, in spite of a possible difference in age and their dissimilarity to those characteristic of other formations, is highly suggestive of the nature of their origin. It is almost certain that the ores of veins are precipitated from solutions, and that these solutions acquire their valuable contents either at great depths and from unknown sources, or from the rock masses adjoining the place of deposition. The latter supposition, which is known as the lateral secretion theory, has been gaining ground of late years, and it has been proved in many cases to satisfy all the known facts. Of granite in particular Professor F. Sandberger has shown that the mica frequently carries various heavy metals, and he has pointed out an exceedingly probable series of reactions by which these metals may have been concentrated in veins. In the granite of Carson district, Owyhee county, Mr. A. Simuudi has detected gold (usually amounting to at least L'5 cents per ton\, besides silver, even at long distances from any known deposit of ore. In view of Sandberger's investigations, it is improbable that this content is due to impregnation from veins. If it be supposed that the Idaho veins are due to metalliferous solutions rising from great depths, it would bo necessary to assume that the granite has had a chemical influence on the precipitation; for if this were due merely to reduction of temperature and pressure, the differences between the deposits in granite and those in the other rocks of the territory would be inexplicable. But the Idaho granite appears to be Archaean, and the lower surface of the Archa3an has never been reached in any part of the world. Whatever may underlie it, it is certainly enormously deep. It would therefore be also necessary to assume that the granite exerted little or no precipitating influence at great depths and pressures, but only within a certain, no doubt large, distance from the surface; for were the precipitating action vigorous toward the lower portion of the granite the solutions would, for the most part, be robbed of their metallic contents at a depth of miles. If this were the case, ore veins, if reached at all, would grow richer and stronger as lower levels were attained. If any rule can be established in regard to the relations between richness and depth, it is rather that veins grow less rich and strong, though strong veins, probably as a rule, continue metalliferous to a greater depth than mining can ever be carried ; but the cases in which veins grow better in proportion to the depth reached are certainly very exceptional. On the other hand, so far as the facts concerning the veins in granite in Idaho are known, the supposition that they are the result of a leaching of the granite itself, probably by heated waters, appears simple, satisfactory, and sufficient. It would account for the difference between the veins in granite and those in other rocks by the difference in the rocks themselves, and place the source of the ores in the neighborhood of their present position. Whether any actual particle of ore originally formed a constituent of the granite on the same level or a few hundred feet below, or even above, no one would of course venture to assert. The hypothesis is merely that the rock in the neighborhood of the veins has furnished their contents. Interesting and in part extremely important oie deposits have been discovered in the sedimentary rocks adjoining the granite area, and, indeed, on all sides of it. It has been asserted that a portion of these deposits form a continuous mineral belt. So broad a statement can hardly be indorsed, but there is sufficient evidence to warrant the assertion that the zone of country immediately surrounding the granite is well worth prospecting with unusual care, and that valuable smelting ores are not unlikely to be met with at almost any part of this zone at or near the granite contact. GEOLOGICAL SKKTCH OF THE PACIFIC DIVISION. 55 Tin- most southerly of Iliis class of deposits are those of the South Mountain and Flint districts, in Owyhee county, near the Oregon line. The country rock is chiefly limestone, and the ore argentiferous galena. No work was done in these districts during the census year or for some time before, not, it is stated, on account of lack of ore, hut in consequence of financial embarrassments arising from the failure of the Bank of California in San Francisco in 1875. To the northwest of the granite lies the Heath district, in which rich galena, high-grade copper ores, iron, and lignite are reported. No description of the country rock has been published, and as the district was idle during the census year the census examination did not include a visit to it; but the association of minerals leaves little doubt that the area is sedimentary. In the Yankee Fork district, north of the granite, the country appears to consist of gneiss (a) and eruptive rocks, while the ores show gold and silver, but seem to carry more copper than in the granite district. The important Custer mine is in this locality. In the Bay Horse district slates are accompanied both by milling and smelting ores, lead and copper being often prominent constituents. Both this and the preceding district were visited by Mr. Williams in the depth of winter, when work on almost all the mines was stopped, and it was impossible to obtain entirely satisfactory suites of specimens. The Wood River country lies southeast of the granite area. Limestone, slate, and granite are the prevailing- rocks, and argentiferous galena (or its products of decomposition), often extremely rich, is the chief ore. As is so usually the case with galena, the ore bodies are irregularly distributed in limestone, but the true meaning of this association has never been fully explained. Mr. Emmons, in discussing the Leadville deposits, regards the galena as precipitated by substitution for the limestone, but no one as yet has indicated the probable chemical reactions involved. Milling ores also occur in the Wood River country in the granite and slate. This region was opened up during the census year, but has since acquired great importance. The geographical distribution seems to indicate that a relation exists between these lead-bearing districts and the granitic area about which they lie. It is altogether probable that the ore was deposited throughout the whole region at the same time or times, and that the differences the character of the ore are attributable to the different chemical and physical characters of the rocks. Were the galena deposits all on one side of the granite it might well be maintained that they were wholly independent of the gold-quartz veins in the granite, but any hypothesis which will account for them independently in their actual distribution appears extremely artificial. 1 :'sides the deposits wluch have been mentioned, there are also veins carrying precious metals in Warren's ramp, in the northern part of Idaho county. The ores from this camp are quartzose, carrying free gold and ores of silver. The association much resembles that met in the mines of the great granite area, and the country rock i ; also reported by Mr. Wolters as granite. Gold mines also occur at Iowa bar, in the extreme eastern portion of the territory. Limestone and "porphyry" are said to be the accompanying rocks. Lignite has been found in various portions of Idaho, for example, in the valley of Boise river and on Reynold's creek, in Owyhee and Oueida counties, etc., but no commercially valuable deposits have as yet been discovered. Sulphur occurs in connection with hot springs in Bear Lake county, and deposits of alkalies exist in the same portion of the territory. Considerable quantities of float cinnabar have been found in Stanley basin, at the eastern extremity of Bois6 county, and along t he Salmon river between the month of Yankee fork and the town of Sawtooth, but not in place. Cinnabar is usually associated with Cretaceous rocks on the Pacific coast, and this fact might be of use in the search for the ore if the horizons of the neighborhood had been identified. Tinstone has been found as wash in the bed of the Jordan river, Owyhee county. This is one of the few points at which tifistone has been encountered in the far west, Temescal, San Bernardino county, California, and Deer Lodge county, Montana, being the principal other localities. The auriferous gravels of Idaho are of great volume and extent. Though of much less importance than those of California, they have been more productive than those of any other state or territory except Montana, and have probably yielded something like thirty million dollars' worth of gold. Three distinct classes of auriferous gravels may be recognized in Idaho. The bars of the Snake river are auriferous, but the gold is in an extreme state of division, and can be recovered at a profit only in exceptional cases. Many rich but small placers occur along the banks of the Salmon and of the other rivers of Idaho, and were either deposited by the present streams during freshets, or left by a comparatively slight shifting of the channels. Small placers have usually been found near the croppings of gold veins, which have undoubtedly furnished the auriferous gravel, and a large part of the veins, as in California, have been discovered by tracing these gravels to their sources. Most of the richest of the small placers have probably been worked out ; at least few new ones of remarkable value have been discovered for many years ; but enough is left to furnish occupation to a considerable population. The deep gravels of Boise basin are of a different character. The basin is surrounded except at one point by mountains, and receives no drainage from beyond its own limits; yet it is estimated to contain tome 125,000,000 cubic yards of auriferous gravel, and some of it has a depth, it is asserted, of no less than -'50 feet. While there is evidence of a channel in a northeastern and southwestern direction, the gravels spread over nearly the whole basin, and occur even on the tops of considerable hills. The gravels extend several miles down Moore's creek, the outlet of the basin, and are here, in part, covered by a heavy basalt cap. The pay-dirt is a A slide of the country rock of the Charles Dickens mine shows a structure usual in highly metauiorphic rocks, corresponding to its microscopical appearance, lint, the constituents are so thoroughly decomposed that little more can be said of it. 56 . PRECIOUS METALS. commonly near the bed-rock of these beds, as is usual elsewhere. Large bowlders are 1'requeut, as aie also fossil- tree stems, which are so characteristic of the auriferous gravels of California. The Boise basin deposits are not worked out, though their yield has decreased during the last few years, owing, it is said, rather to high wages and lack of water than to dearth of good gravel. In the earlier days of mining in Bois6 basin many extremely rich bars were found, which were undoubtedly concentrations from the older gravels by modern streams. Pew, if any, of these rich spots can have escaped the eager search which has been made for them. It would be impossible to account for the presence of the gravels of the Bois6 basin at the head of a system of drainage without a special examination undertaken for the purpose, but it may be considered certain that a great river once flowed through the basin and transported the gravel. Some secular or paroxysmal action, not improbably a concomitant of the basalt eruption, must have modified the topography in such a way as to deflect this river, but the character of the change in the drainage is unknown. The Bois6 basin gravels were probably contemporaneous with those of California ; for the present rainfall, as has already been pointed out, is insufficient to account for them, and it is not probable that greatly increased precipitation can have prevailed in either of two districts so similarly situated as California and Idaho without its being shared by the other. The fossil plants also seem to be the same or extremely similar, as are also the relations to the basalt. The following sections of gravels are selected out of a considerable number to illustrate their occurrence. The third of these is noteworthy as an exception to the ordinary rale that the pay-dirt lies near the bed-rock. CREPISCULLA HYDBAUL1C MINK. MOOKE'S CREEK DISTRICT, BOISE COUNTY, IDAHO (SECTION IN NORTH WORKINGS). Brown soil 1 1 Uniform low-grade gravel of median) size III I Bowlder stratum (quartz and granite) IV | Bed-rock granite ; hard when first uncovered, slacking rapidly on exposure. ' C None absolutely barren, but tbe bulk 47 feet. > Maximum. 70 feet < of the gold is thought to come from ] O-'O feet ' the lowest quarter of the bank. The bank shows a fine section across the river bed 550 feet wide, which is now left at the summit of a low hill. Ibis part of the claim is from 360 to 450 feet higher than the south workings. R. VV. SPENCER'S HYDRAULIC MINK. BOSTON, BOISE COUNTY, IDAHO. II m Loam, with some small quartz bowlders 3 feet. > Maximum, 10 feet ; average, Quartz, gravel, and clay, with small bowlders not over 9 inches in diameter, I 3 feet, t chiefly granite. Bed-rock ; soft, decomposed granite. ( Grass-root gold. Color throughout ( deposit. Best pay on bed-rock. NOBLE, LOWER & MANN HYDRAULIC MINE. MOORE'S CREEK DISTRICT, BOISE COUNTY, IDAHO. I II III IV Soil..... t 2 feet, 1 Quartz, gravel, and clay . . I 2-6 " Rotten bowlders of quartz and granite, 9 inches to 4 feet in diameter I 10 Bed-rock granite; very rough, hard when first uncovered, but slacking rapidly on exposure. p ( * i Maximum, 30 feet ; \ Tj pper 3 f ee t from surfaeois the pay- f average where work- \\ ing portion. -15 feet, ) in S. 13 feet- River bed 300 feet wide and 2,000 feet long on claim. The bowlder stratum, III, is too poor to pay for wwVing by itself, but all has to lie piped off to obtain grade for race one-fifth good pay and lower four-fifths low grade. SUMMARY BY COUNTIES. ADA COUNTY. There is very little mining in Ada county, the principal industry being agriculture. The occurrence of galena not far from the granite area of the adjoining counties, however, is an interesting fact, though no work was done in the Heath district, where it occurs, in the census year. ALTURAS COUNTY. The western portion of Alturas county, together with Boise county, forms a great granite district, chiefly drained by the Boise river and its tributaries. The veins in this granite carry a quartz gangue, with gold and silver ores. In some the one metal predominates, in some the other, but as a rule both are present. The ores are free gold and auriferous pyrite, native silver, both ruby silver minerals, stephanite, freibcrgite, horn-silver, and galena. The gangue minerals are quartz, pyrite, chalcopyrite, mispickel. zincblende, and a little calcite, Molybdenite is also reported. Nearly all the veins dip at an angle of over 45, and the majority strike northeast and southwest, following the trend of the mountain ranges. To the southeast of the granite, in the Wood liiver country, there are deposits in limestone of galena and its decomposition products, accompanied by copper and iron minerals. Milling ores are said to have been found in the slates of this region since the expiration of the census year. There are also small placer deposits on the Salmon river and its tributaries in this county. GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 57 ALTUKAS. . UuUiriiiiuuiiuuB in parentheses are given on the authority of the experts.) Mine. WALLS. Ore and gaugue. Foot. Hanging. Charactet of deposit (Gold, galena, antimony, argentiferous sulpbarsen- ide and sulphantimonide minerals, zincblende, pyrite). quartz, andcalcitc. BONAPARTE. Bonnpartc Consolidated. IIAUD6CKAH1II.K. Crown Point Bonanza (Gold), quartz Emma do General Grant Gold quartz and limonite NcwOphir Cold quartz, pyrite. mispickel, galena, and (zinc- blendej. MIDDLE nOIBE. Jessie jienton Kuby silver, quartz. pyrite, chalcopyrite, (arsenical and autimonial silver ore, with auriferous pyrites). Buffalo (Dark and light ruby silver, native silver, auriferous pyrites, and quartz.) Buffalo and Atlanta (Aoiilerons pyrites, argentiferous siilpharsenide.s and sulphaniimomdes, quartz, and molybdenite.) Last Chance Gold, auriferous pyrites, ruby silver, and quartz Monarch Dark ruby, horn-silver, native silver, quartz, pyrite, and probably mispickel, (light ruby, auriferous pyi ites, free gold, and traces of copper). Taliiuita Argentina, an argentiferous sulpharseuide, quaj-tz, (rnliy silver, native silver, and a little free gold). Ynba Tunnel (Gold), quartz feldspar, pyrite. and mispiekel. MINERAL HILL. Idahoan Kicli argentiferous galena Jay Gould Galena and eciussite Granite. Granite ". ! Vein. (Granite) . ..-..do ....do ...do ... (Granite) ...do... do. .do (Granite) (Gran itcj . .. do . . do. .. do. do ....do.... Granite. .do. (Limestone) ...do .. tlUBEN'B KIVKR. Joe Daly ' Free gold, quartz, mispiekel. and limonite Mammoth Quartz and galena, (native silver, free gold, light and dark ruby silver, and auriferous pyrites). Silver <;laiicc Quartz and galena, (stephanite, native silver, light ruby silver, pyrite, and a little gold). Washington Quartz and galena, (free gold and base sulphides) KI;J> WAKBIOB. Donnybrook Fair Quartz Colorado, (gold, pyrite. antimoniiil ores. No silver). New York do Wide West do Wildcat Quartz and misptckcltXgold and silver in rebellions compounds). Vietor Quartz Colorado, (gold) KUCKY BAH. Alt uras Gold Hill Gold, quartz, pyrite, and mispiekel Idaho- Vishnu Gold, galena, quartz, pyrite. and mispiekel. SAWTOOTH. Columbia Quartz, probably horn-silver and frei'nergite, (ruby silver). Pilgrim Quartz and j'reiliergite (ruby silver.) : Lucky Boy ; Quartz and horn-silver Granite .. (Granite) ...do .. .do ...do... Granite .. do .. Vein. Do. Do Do. Vein. Do Do. Do. Do. Do. (Limestone). Do. Granite Vein. (Grardtci ! Do. do do. (Granite) (Granite) .dp. .do do do .do .do. .do .do. Do. Do. Vein. Do. Do. Do. Do. Granite Granite : ! Vein. ...do... ...do ! Do. (Granite) (Granite) ! Vein. .do. .do. do. do. Do. Do. BOISE COUNTY. This county is, for the most part, in the grauite area mentioned under Alturas county. The veins carry chiefly gold, except in the Banner district, where the silver is in excess. The placer deposits of this county have hitherto been the most important in the country outside of California. Their character and occurrence have already been sufficiently described. PRECIOUS METALS. BOISfi. [NOTE Determinations iu parentheses arc given on the authority of the experts.; Mine. Ore anil gaugue. Crown Point A sulpharscnido of lead, probably dufreynoysito, quartz and pyrite, (ruby "silver, horn-silver, mis- pickel, sulphur, and copper compounds). I'aiianiint ' Quartz, (ruby silver) CASON CEEKK. i 'eiitennial ! Gold, quartz Colorado Ebenozer \ Gold quartz, iron and copper pyrites, and mis- pickel. GAMimiXCS. Sub Rosa Gold quartz GRAMTE. Gold Hill | Quartz and pyrite, (gold). MOORE'S CHEEK. Crepisculla Ilydranlic Thorn Creek Hydraulic SHAW'S MOUNTAIN. North Star. Gold quartz ... Paymaster ! (Gold) quartz . (Gold gravel) .. do... Foot. Granite diabase. Hanging. Character of deposit. Granite Granite Granite... Granite dike | Vein. Granite Do. Granite Vein. Granite ' Granite Do. Granite* . Vein. Granite I Granite Vein. Granite I.- I Placer. .. do | Do. Granite Granite Vein. (Granite) Rising Sun Gold quartz, galena, copper, pyrite, and probably Granite. mispickel, (fiee sulphur). (Granite) Granite Do. Do. * Microscopically examined. IDAHO COUNTY. This county appears to contain an isolated granite area in tbe neighborhood of Warren's camp and Florence. The quartz veins are much the same in character as those in Bois6 county, and are accompanied by small deposits of auriferous gravels. IDAHO. [NOTE. Dctermiuatious in parentheses are given on the authority of the experts.) WALLS. Character of Foot. Hanging. deposit. WARREN'S CAJIF. ; Vein. quartz. LEMHI COUNTY The important mining districts of Yankee Fork, Mount Estes, and Bay Horse lie in the southern portion of this county. In the Yankee Fork district the principal rocks appear to be gneiss and an eruptive which is possibly rhyolite. (The workings were superficial, and the specimens were too much decomposed for determination.) Free gold and silver minerals are accompanied by quartz, pyrite, and copper ores. In the ]>ay Horse district the country rock is slate, and the ore consists of argentiferous galena, with copper minerals and traces of gold in a quartz gaiigue. LEMHI. [ NOTE. Determinations in parentheses are given on the authority of the experts. | Mine. Ore and gangne. WALLS. Character of deposit. Foot. Hanging. BAY HORSE. RaniRhorn (Argentiferous galena, gray copper, a little chloride and bromide ol silver, copper carbonates, traces of gold, hematite and quartz.) (Slate) Vein. Vein. Do. Do. YANKEE FOBK. Charles Dickens General Cuater Quartz, pyrite, and probably stephanito, (argentite). Same as General Cnster Indetermiuablv decomposed yellow porphyry (locally called rhyolite). do Vnknown ... do * Microscopically eiamiuod. GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 59 OWVIIEK rpvNTY. The mining districts of Owyhee county lie about Silver City and 'Wagontown, on the Jordan river. This region is separated from the granite region of Alturas and Boise counties by the Quaternary plains of Ada county, but it is extremely probable that the granite of Silver City is a portion of the larger mass to the north. To the southwest of Silver City the surface is occupied by quartz-porphjry overlying metamorphic rocks in part, and both porphyry and granite are intersected by dikes of basalt. The ores are similar to those of the northern granitic area: gold, silver, freibergite, and sulphurets in a quartz gangue. The veins follow the general trend of the mountains to the northwest and dip at high angles. As usual, small placers accompany the gold veins. In the South Mountain district, near the Oregon line, galena occurs in limestone. Coal has been found, but only in insignificant quantities. Tinstone has been identified as float in the Jordan river. OWTHEE. [NOTE. Determinations in p-renthesos are- given on the authority of the experts.) WALLS. Character of Foot. deposit. Hanging. CARSON. Black Jack calc-spar, cupper stains). (Granite) (Granite) Do Florida Hill IdlewiUl (Five gold and argentiferous sulphurets, quartz) . 'do do Do Granite .... Do Rath AV;ir Ea""lr ProbaUy arg ntite, quartz Granite of somewhat gneis- soid structure. (Granite) Gninitt- of somewhat gneifl- Do. sold structure. (Granite) Do WA<;O.NTOWN. Ohio deteniiinabta, quartz. (Porphyry) Do Web foot (Porphyry) Do Microscopically examined. OTHER COUNTIES, In Oneida county gold quartz veins and placers are worked at Cariboo and Iowa Bar, and along the course of the Snake river in this and Cassia counties gold washings are conducted on a small scale. The northern counties of Kootenai, Nez Perce", Shoshone, and Washington contain gold quartz veins and placers, which are not, however, worked to any considerable extent, and the conditions of their occurrence are not known. Salt and sulphur are obtained in Bear Lake county. 60 PRECIOUS METALS. .CHAPTER II. GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. BY S. F. EMMONS. lu the following pages the writer has endeavored to present u brief outline of the geological structure of the states and territories of this division as far as it bears on the ore deposits of the region, the geological occurrences of the ore deposits themselves, and their mineralogical composition as far as it has been possible to determine them. Such a sketch at the present time must, from the nature of things, be extremely unequal, and, at its best, very incomplete; but it has seemed best to give it in this incomplete form, even if it, merely serves to show the gaps in our knowledge and to encourage others to fill them up. The importance of the geological relations of mineral deposits has been hitherto very much underestimated, chiefly for the reason that so few competent men have given attention to their study. For this reason geological literature contains but little trustworthy information on this subject. The material here presented has been in part compiled from data and specimens gathered by census experts, and in part from reports of government surveys, from reports by individual geologists upon mining districts, unfortunately too few in number, and from the personal observations of the writer in portions of Wyoming and Colorado. There was difficulty in obtaining men who had at the same time a knowledge of field geology and a practical acquaintance with mines, and the limited time at the disposal of those to whom the work was intrusted rendered it practically impossible to visit every mining district. Of the specimens of ore, gangue, and country rock which it was intended should be obtained from each mine a large proportion were in a too far advanced stage of decomposition for satisfactory determination. In many cases no specimens accompanied the schedules. Hence the tables of mines, country rocks, and ores which accompany the following sections are incomplete in many important instances; but it has not been thought advisable for that reason to refrain from publishing them, even in their imperfect condition, since they contain many data useful to mining engineers, and will serve as a skeleton which may hereafter be more completely clothed as additional material is obtained. In cases where no specimens were at hand it is indicated in the table, the information given being on the authority either of the experts themselves or of some person connected with the mine. At the end of another decade it is hoped that our knowledge of these important mining regions will be such as to render it possible to present the information which is here outlined in a comparatively complete form. The maps which accompany these sketches are intended as a guide to the reader unacquainted with the geography of the country, and will serve to show those who are already somewhat familiar with it the county divisions, which have been followed in the treatment of each section. An attempt has also been made, in a very general way, to iiMlicate by colored dots the relative distribution among actually producing mines of ores in which gold or silver predominate. These are given, as well as the rest of the material, rather as a sketch than as a finished and accurate delineation. GEOLOGICAL SKETCH OF COLORADO. The state of Colorado, which is included between the .'J7th and 41st degrees of north latitude and the 25th and 3Hd degrees of longitude west from Washington, has an area of 103,045 square miles. This area may be divided into three meridional belts: a plain belt, comprising a little over one-third of the eastern portion of the state; a mountain belt, lying next west of the former, and covering also about one-third of the state ; and a narrower belt on the west, which is largely a mesa country, and belongs to the so-called Colorado plateau region. According to the classification of Lieutenant Wheeler's maps, only about one-fifteenth of the whole surface is arable land, but at the time this classification was made probably only the alluvial bottom lauds of the larger streams were assumed to be available for agricultural purposes. This restriction may hold good for the mesa region, but with the late rapid increase in the population of the state increasing areas of plain country to the east of the mountains have been brought under cultivation by means of irrigating ditches, and the results obtained have shown that the soil is exceptionally favorable to agriculture, the extent to which it can be profitably carried on being probably limited only by the feasibility of irrigation. A large portion of the plain country is covered by a porous, crumbling, homogeneous soil, filling irregularities of the rock surface beneath to depths of from 5 to 20 or more- feet, whose external appearance strongly resembles that of the famous loess which has proved the, source of fertility of many important agricultural regions in the world. As yet no systematic studies have been made of the geology of the plain country, and the actual extent and eh;ir;>rfor of this deposit is not definitely known. It seems probable, however, that it may at least be analogous GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 61 to tin- loess \vliidi hns been proved to exist farther east, in Nebraska and Kansas. An analysis of this soil, taken from the neighborhood of Golden, close to the foot-hills of the mountains, made in the laboratory ( .r the I'nited States geological survey at Denver, gave the following results: IVr rent sili4 Scsi|iiiosile of iron .., I. t;;;!i Lil1 "' 1.14? Magnesia ;.. Q.944 Potash 3.748 Soda '2.472 Water and organic matter 1_ 79; Phosjiliorir acid 0. 228 09. 981 The lime and magnesia in this soil are in considerably smaller proportions than in ordinary loess soils, but at least 50 per cent, of the material may be supposed to be free quartz. It may be assumed, therefore, that at a greater distance from the mountains the proportion of silica will be smaller, and the more soluble and easily transportable salts greater. The same soil about 10 miles to the east of Denver, or 20 miles from the foot of the mountains, yielded 4.5 per cent, of lime and 0.8 per cent, of magnesia in a soluble form, probably as carbonate. The climate of Colorado is essentially a dry one, though less so than that of New Mexico. In summer there are often showers, but they are too uncertain to be depended on for agricultural purposes. ARTESIAN WKLLS. The extent to which agriculture may be carried on is therefore dependent mainly upon the amount of water which isavailable for purposes of irrigation. The various streams which emerge from the mountains yield a sufficient supply for a comparatively narrow belt along the foot-hills, but, owing to the rapid evaporation which takes place in this dry climate, they cannot be counted on for irrigating the lands at any great distance to the eastward. Artesian wells have been suggested as another source of supply, and government aid has been called in to make practical experiments, with a view to determining whether these wells will yield water in sufficient amount for purposes of irrigation. The water supply of artesian wells is supposed to follow the laws of hydrostatic pressure: that is, where the surface water, penetrating the earth from the surface, reaches an impermeable stratum, it follows the inclination of that stratum as an underground stream. If, then, this stratum be reached by an artesian boring at a point where the surface of the ground is sufficiently below the outcrop of that stratum, the water, seeking its original level, will flow out through this boring to the surface. The structural conditions on the great plains are theoretically favorable for obtaining flowing wells. The sedimentary formations which underlie them are upturned at their western edge against the foot-hills of the mountains, and are thus accessible to the waters which drain their surface. The surface of the plains slopes regularly to the eastward, although at a very gentle angle; so that to obtain the required difference of level it will be necessary to go some distance from the mountains, as it is found in practice that the water from artesian wells does not strictly fulfill the condition of finding its own level, but that a certain portion of the difference of elevation is lost probably by friction and the want of a perfectly free underground circulation. Of the sedimentary formations the Tertiary beds lie horizontal and are not upturned, and these, owing to their porous character, probably would not carry the required supply of water. It is advisable, therefore, to avoid sinking the wells where these still exist, and fortunately their present area is probably limited. Of the Mesozoic beds, the upper formations (the Cretaceous) are largely composed of sandstones, which are also porous and more or less permeable to water. They contain also, it is true, beds of clay, but it cannot be certainly stated that these clay beds are continuous over any great areas. It is questionable, therefore, if the Cretaceous formation will yield a large supply of water, except locally, as near Denver, where a synclinal basin is formed by a slight fold in tin- strata to the east of it. In the Jura, below the Cretaceous, the conditions seem more favorable, as they contain a considerable amount of clay and a comparatively persistent limestone bed. The Trias is a formation largely of sandstones, and therefore not favorable, and it is only when the Carboniferous is reached, which is made up of compact and evenly-bedded limestone, that we come to strata which arc beyond doubt capable of carrying the required supply of water. The thickness of these different formations has not yet been accurately determined ; but it may be assumed at the foot-hills that the Cretaceous beds are at least 3,000 feet in thickness, and the Jura and Trias 2,000 more, [t will be seen, therefore, that it may require a boring 5,000 feet in depth to give a permanent and considerable flow of water. On the other hand, there arc good grounds for supposing that the thicknesses of t he different formations decrease to the eastward, and this supposition has been in part continued by actual observation along a line near the southern border of the state. It is probable, therefore, that at a sufficient distance to the eastward the thickness of the beds overlying the Cretaceous formation will be very much less than the figures above given. In the present state of our knowledge these, are largely matters of conjecture, and it is only by the actual experiment of boring wells that the thickness and water-bearing properties of the different formations can be determined. It is evident, however, from what has been said, that these experimental well* should be sunk near the eastern border of the state, and at points where the greatest thie.kin.-ss of the upper beds is likely to have 62 PRECIOUS METALS. been removed, bringing the deep-seated water-currying bed, therefore, nearest Hie present surfaces. To determine these points with accuracy, however', would require an accurate and systematic topographical and geological survey, which has not yet been made, and the choice of the right location must be largely a matter of chance. It seems probable, therefore, that with its exceptionally favorable conditions of climate and a soil of this character the agricultural resources of Colorado are yet but partially developed. COAL Its industrial possibilities, if gauged by its natural resources in coal, the indispensable basis of almost every industrial enterprise, are almost unlimited, not less than two-thirds of the area of the state being underlaid by the coal formation. While over a great portion of this area it may lie too deep for profitable extraction, and while coal beds are by no means necessarily continuous in any particular formation over very large areas, yet the geological conditions are such that a relatively large proportion of this formation is brought to the surface and rendered available for practical working, especially along the borders of the mountain belt. Along the eastern front coal mines are already opened and working at intervals from the northern to the southern boundary of the state. Mines are also worked in the South park, in the center of the mountain belt, and in Guunison and La Plata counties, on the western slope, while the developments in many other localities are only awaiting railroad communication and an industrial demand. MOUNTAIN BELT. The precious-metal production of the state is derived mainly from the mountain belt, as might have been assumed on a priori geological grounds, reasoning from which none would be looked for in the plain country; nor wo 1 aid much be expected from the mesa region, except where eruptive rOcks have protruded through the sedimentary strata and formed such isolated mountain groups as the Sierra la Sal, Sierra Abajo, Sierra el Late, and others. The topography of the mountain region and the plateau country on its west, as well as its general geological structure, is pictured on the maps of the Hayden survey, of which the extreme northern strip is taken from those of the Fortieth Parallel. The most important group of rocks there represented, and intimately connected with ore deposition, viz, those of Mesozoic or Secondary age, have either entirely escaped recognition or have been classed indiscriminately as belonging either to the volcanic rocks or to granites. The mountain belt of Colorado, which in this latitude is generally known as the Rocky mountains, to distinguish it from the other principal Cordilleran systems to the westward, the Wahsatch and the Sierra Nevada, has, taken as a whole, a due north and south trend. When examined in detail, however, it is found to be made up of a number of more or less regular chains or ridges having a general trend to the west of north, standing en echelon or with their ends overlapping each other, with mountain valleys of greater or less extent between them, as the result of which structure the mountains in general seem to be divided up into two chains, with large included valleys which have received the name of "parks". The general name of Colorado, or Front, range has been given to the eastern of these divisions, and that of Park range to the western. The North, Middle, and South parks and the San Luis valley are the larger of the included valleys, the three former, with the smaller Wet Mountain valley to the south, being really a portion of the same continuous line of depression, while the valley of the Upper Arkansas stands in the same relation to the San Luis valley. The eastern front of this range presents a comparatively regular north and south line, broken here and there by bay-like valleys, running up into the mountains in a northwesterly direction arid following the prevailing trend of the echelon ridges. The most important of these are the Manitou and Huerfano parks and that which extends up Oil creek from Canon City. These in earlier geological times were actual bays in the seas in which the Palaeozoic and Mesozoic rocks were deposited, while the parks were partially inclosed arms of those seas. The western front of the mountains is, however, much more irregular, and is broken by branching mountain groups extending out, also with a general northwest trend, into the mesa coujitry of the Colorado plateau. The principal of these outlying mountain groups, commencing on the north, are the Elk Head mountains, the White River plateau, the Elk mountains, and the San Juan mountains, in all of which, as will be seen later, there is a very great development of eruptive rocks. GEOLOGY. The geological history of this mountain region is, briefly and in its most general outlines, as follows : At the close of the Archaean era, or in the Cambrian ocean, a large area, covering most of what is now the Colorado range, formed a large rocky island, with a number of minor islands lying to the westward, the most important of which was that which now forms the Sa watch, from which it was more or less completely separated by the waters occupying the present depressionsof the North, South, and Middle parks. During the whole of the Paleozoic and Mesozoic eras a continuous sedimentation went on in the seas surrounding these islands of material derived from their abrasion. The geological record, as far as it has been studied at the present day, gives evidence of no great disturbance during this long period, although it is probable that local elevation and subsidence might have taken place; and there is some evidence to show a general subsidence of the whole area, which gave a somewhat larger field of deposition to the later sediments of these periods. Toward the close of the Cretaceous period, at the time of the formation of the coal beds, the seas became shallower, owing to a general elevation of land, and considerable portions of the outlying areas were partially inclosed. During this time, and possibly earlier, immense masses of eruptive rock were forced up through the already deposited sediments which were still beneath the water. Unlike the lava flows of modern lays, however, these molten masses were not, as a rule, spread on the surface of the rocks, but congealed before they reached it, either in large masses, in dikes, or in sheets spread out between the beds. It is impossible to say GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 63 li'.\v long before (lie close of the Cretaceous period the eruption of these Secondary igneous rocks commenced, but it is known that in certain localities it must have continued nearly to the close of the period. At some time after the close of the Cretaceous period a general dynamic movement took place in the Rocky mountains, by which tin- existing mountain ranges or islands were crushed together, broken, and elevated, and considerable areas of the adjoining sea-bed were lifted above its surface. In the general continental elevation which followed fresh-water lakes or inclosed seas were formed, in which, by the degradation of the newly-made land areas, considerable sediments were deposited. The outlines of these Tertiary seas, owing to the nature of the deposits made in them, which were easily eroded and carried away by subsequent atmospheric agencies, cannot be yet definitely determined. It can only be said that their area and location were frequently changed, and that during the Tertiary era, and subsequent to it, eruptions of igneous rock occurred, generally following the lines of earlier eruptions, but, unlike those, spreading out on the actual surface of the land, and in some cases beneath the sea. While the general form of the mountain area, as has been shown, was determined iu the very earliest geological times, it is only since the Tertiary era, and in a great measure by erosion subsequent to the Glacial period, that the present sculpturing of the mountain forms and carving of the valleys have taken place. At what period during this history the different mineral deposits of Colorado were formed it is as yet impossible to say with any degree of definiteness. The gold deposits of Gilpin county in the Archaean may, like those of the Black hills of Dakota, be of pre- Cambrian age. It is probable, however, that some of these at least, and the silver deposits iu the adjoining counties of Clear Creek and Boulder, were subsequent to the intrusion of the porphyries, which are presumably of later date. The silver deposits of Leadville are known to have been formed subsequent to the Carboniferous and previous to the dynamic movement at the close of the Cretaceous. Some of the silver deposits of Guunison, on the other hand, must have been later than the Cretaceous, while those of Custer county and the San Juan region are in part at least presumably of post Tertiary age. ORES. The ores of Colorado present an almost infinite variety of miueralogical composition, so that it is difficult to formulate any general laws with regard to their distribution or manner of occurrence. Of the actual precious- metal production of the state, by far the largest portion is derived from pyrites and galena and their decomposition products. The telluride ores of Boulder county and the auriferous pyrites of Gilpin county, with a few individual deposits in the southern portion of the state, constitute the source from which its gold is derived. With these exceptions its mineral deposits may be considered as essentially silver-bearing. The principal source of silver, as has already been stated, is argentiferous galena and its decomposition products, while argentiferous gray copper, or freibergite, is next to this the most important silver-bearing mineral. The sulphides of silver also occur, and in some cases bismuth is found in sufficient quantity to constitute an ore. As yet, so far as known, no copper is extracted from the ores of the state, except as an adjunct in the reduction of silver-bearing copper ores. Placer deposits are generally confined to the valley bottoms among high mountain ridges, and while they are locally of considerable value and importance, and were the original attraction which brought the mining community to the state, their present yield forms a very inconsiderable proportion of its precious-metal production. Prior to the discovery of the silver ores of Leadville mining in the state was principally confined to approximately vertical veins either in the Archaean rocks of the Front range or the eruptive rocks of the San Juan region ; but since the limestone deposits of the Mosquito range have proved so exceptionally rich the attention of prospectors has been more and more turned to the ores which occur in sedimentary rocks, and many new districts have been discovered, but none to rival that of Leadville. As regards geological distribution, gold is found in the Archaean and in the eruptive rocks of the Secondary age. In the sedimentary formations it is comparatively rare in limestone beds, but is not infrequent in siliceous beds. Silver is also found in the Archaean and in the Secondary eruptive rocks. In the sedimentary beds, on the other hand, it is more common in the limestones, although it is not exclusively confined to them. By far the greater portion of this metal produced in the state is derived from the limestones of the Palaeozoic formations. The most important generalization to be made with regard to the distribution of ore deposits is one that has been already noted in other countries, viz, that the largest and most important ore deposits are found where igneous rocks are most abundant. The experience of the writer leads "him to further modify this by saying that it is the eruptive rocks of earlier age than the Tertiary volcauics with which valuable ore deposits are generally associated. The mineral wealth of the state is by no means confined to the precious metals. Its coal beds are widespread, and contain both bituminous and anthracite coals. Gypsum beds are of frequent occurrence in the Triassic and Upper Carboniferous formations, and salt springs are not infrequent, and probably derive their supply from the same horizon. The Dakota group of the Cretaceous on the eastern foot-hills carries beds of most remarkably pure fire- clay. Excellent building-stone is quarried from the Archaean, which furnishes red granite ; from the Mesozoic formations, which furnish white and red sandstones and valuable fiags ; and from the tufaceons rhyolite-lava beds of the plains. 04 PRECIOUS METALS KA STERN COUNT! K*. Weld, Arapahoe, Blbert, and Bent counties, and the eastern portion of Las Animas, lie entirely in the plain region east of the mountains. Their surface is covered to a depth of from 10 to 20 feet by a light, porous, almost loess-like soil, which is admirably adapted to agriculture wherever it is possible to bring water for purposes of irrigation. Where this is not possible, the natural grasses arc- most valuable for the raising of stock. No metallic minerals are to be looked for in this region, but it is underlaid by the rocks of the coal formation, which must contain extensive and valuable beds of this mineral, whose development is only dependent on the market demands and the depth below the surface at which it occurs. LARIMER COUNTY. This county includes the northern end of the Colorado range in Colorado, and, although mostly a mountain district, has as yet developed no considerable mineral wealth. One reason of this may be found in the fact that the range is here mainly made up of Archaean granite a coarse, red, crumbling rock, which is characteristically developed at Sherman, on the Union Pacific railroad, and which has in this state thus far proved barren of metallic minerals. A lurther reason may be found in the comparatively limited development of Secondary eruptive rocks, which, so far as known, occur only in the western limits of the country bordering on the North park, at the head of Grand river. Mines have already been discovered near the western boundary of the county, at the head of Laramie river, in the Medicine Bow range. GRAND COUNTY. This county includes the North and Middle parks, whose surface is mainly covered by Mesozoic rocks, and are separated by a cross-range of eruptive porphyry and volcauics. In the Archaean mountains which inclose the county, and still more in the eruptive range which divides the two parks, the geological conditions are favorable for the formation of valuable deposits of minerals. As yet, however, owing to the difficulty of access and want of railroad connection, no important mines have been developed, and data from the few mining districts that exist within the county are entirely wanting. The coal-bearing formations originally covered the greater part of both park areas, but these have been removed in part by erosion. ROUTT COUNTY. This county, which extends from Grand county west to the Utah line, comprises the valleys of the Tampa and of the Little Snake rivers, which are underlaid by coal rocks, whose deposits come to the surface along the borders, but in the centers are too deeply buried beneath the overlying Tertiary beds to be practically available. These deposits, as elsewhere, afford no promise of metallic minerals. In the bordering mountains the only known mineral developments are the placer mines of Halm's Peak district, which are found in the angle between the Archaean uplift of the Park range and the volcanic group of* the Elk Head mountains. These placer deposits are evidently derived from the disintegration of Archaean rocks, and have yielded a small but constant return for many years past. Near the junction of the Elk river with the Yampa is an extremely interesting group of mineral springs carrying sulphur and free carbonic acid, known as the Steamboat springs. The coal-bearing Cretaceous formations occupy the valley of the Yampa river and a great part of the ridge which divides it from the White river on the south. Favorably situated outcrops are abundant, and only await the advent of railroads to become of practical value. BOULDER COUNTY. TOPOGRAPHICAL. The mines of Boulder county are situated on the eastern slope of the Colorado or Front range, not far from- the town of Boulder, which lies at the month of Boulder canon where it debouches on the plains. The district containing the mines extends about 13 miles in a north and south direction, and from 4 to 10 miles from east to west. The country is drained by a number of creeks, which cut deep canons between the mountain spurs. These are, commencing on the north, the south branches of Saint Vrain creek, then James (popularly Jim) and Left-hand creeks, which join a little below Jamestown and flow out on the plains, as Left-hand creek, into the Saint Vrain at Longmont; next the various forks of Boulder creek (Four-mile, North Boulder, and Middle Boulder), which flow past the town of Boulder in a single stream, and also are tributary to Saint Vrain creek. The town of Boulder is connected by the Colorado Central railroad with Denver on the south and Cheyenne on the north, and by the Boulder Valley railroad with the Denver Pacific railroad. A narrow-gauge railroad is also projected from Denver to run up into the/mountains via Boulder. There are a number of small mining districts in this region whose limits were not definitely ascertained, but they are not in themselves important, except for purposes of descript ion. The mines on the Saint Vrain are generally included in the Saint Vrain district. On GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 65 James creek is the Central district. South of Left hand creek is the Gold Hill district, with the Sunshine district nearer the foot-hills, and at the head of this creek is the Ward district. Still south of this, between Four-mile creek and North Boulder, is the Sugar-loaf district, and south of Boulder creek Magnolia district, while at the head of Middle Boulder creek is Caribou or Grand Island district. GEOLOGICAL. The general geological structure of the district is simple and typical of the mining districts on the eastern slope of the Colorado range. Along the foot-hills immediately adjoining the plains is a series of so-called hog-backed ridges, formed by upturned Mesozoic strata resting on the Archaean core of the range. These upturned sedimentary beds form a fringing belt, of a width varying with their angle of dip, along the entire extent of the eastern foot-hills. Just south of Boulder their angle is almost vertical, and they form a prominent peak, rising to au elevation of over 8,000 feet, or 3,000 feet above the plains. The upper member of the sedimentary series, the Laramie or Lignitic group, contains valuable coal deposits, whose outcrops, by erosion at Boulder, have been moved out some distance on the plains. Besides coal, these beds furnish admirable building-stone and flagging, and also fire-clay and lime. Of metallic minerals, however, they have as yet proved barren. The Archaean rocks immediately adjoining the plains have generally been found to contain but few valuable minerals, and it is not antil the range has been penetrated for a distance of several miles that prominent deposits appear. In Boulder county the mines are found within 2 miles of the plains. The Archiean rocks of the Boulder district consist mainly of gneiss, intersected by veins of pegmatite (or coarse-grained secondary granite) varying in width from a fer inches to 40 or 50 feet. In addition to these there are later eruptive rocks of Secondary age, occurring either in dikes or massive bodies, of whose extent and character only imperfect data are obtainable. The prevailing gneiss of the region is of a type of rock oot uncommon in other mining regions; and for purposes of description the name u granite- gneiss'" has been adopted for this, for the reason that it is largely a massive rock, in which the bedding is -either indistinct or not at all visible. At times this gneiss is coarsely crystalline, at others tiue-graiiiied, in which case the proportions of hornblende and biotite are relatively greater and the rock assumes a darker -color. Quartz is alwa\ s prominent in it. In the coarse rock two feldspars are visible, an orthoclase feldspar. generally of a delicate pink tinge, and a white opaque feldspar, which is tricliuic, and frequently shows the characteristic striataon on the basal cleavage faces. In a specimen from the eastern base of Sugar-loaf, examined microscopically, plagioclase feldspar is largely predominant, and is of two varieties, one probably oligoclase, the other labradorite. Magnetite, apatite, and pale zircons are sparingly present. This granite-gneiss generally forms rounded hills with extensive debrts slopes, and presents but few prominent or angular outcrops. The pegmatite vein*, or gangue*, as they are locally called, are mostly composed of white feldspar and quartz. Parts -of them are coarsely granular .and contain some mica, others are like a fine-grained granite, and in still others these two textures are found bearing irregular relations to each other. Sometimes they are notmore than a finger thick, crossing the rock in every direction without intersecting each other, and sometimes they consist entirely of quartz. Two of these veins have strongly marked characteristics, and have been traced for a number of miles through the district. The first, the Maxwell gangue, runs a little east of north from Four-mile creek to Left-hand creek, crossing the road to Sunshine, tw miles from Boulder, andis said to carry pyrites and some tellurides. The Hoosier gangm 1 . whicli is supposed to form the westenm limit of th-evfcelluride belt, is about 30 feet in width, and runs through Gold HUl in a direction east of notfth. A specimen examined in this belt, is like fine-grained granite in appearance, though consisting chiefly of quartz and feldspar, with "Mack metallic particJes macroscopically visible. The microscope shows .only quartz, orthodase, microdiue, the remnants of biotite a,n4 titauite, and apatite in small prisms. The quartz contains fluid inclusions and Ihair-like taicrolites of rutile. Tikis carries silver ore and gray copper. The j tellurkle belt includes the Magnolia, Sugar-loaf, 4*old Hill, and part f the Central districts. In this belt eruptive rocks are very rare, but tlve pegmatite veins are extremely common. West of this region are enormous masses of eruptive rock, and tellurides are not foaind. In the Caribou district are rich siK'er ores -carrying from 39 to IL^SOO ounces of silver to the ton. and in the Ward district veins carrying free gold, with iron aasd copper pyrites, which have a general direction east and west while the others are more nearly north and south. Of eruptive rocks, that which forms tiie Sugar-loaf, a conical hill between Four-mile and Boulder creeks, is a fine- grained porphyritic rock of grayish color, showing in the hand specimen small white feldspars, biotite, hornblende and titanite, the latter, of a yellow color, being quite frequent. Under the microscope the rock shows some augite and a crystalline grouudmass containing a little quartz, but it is made up chiefly of feldspaV, in rounded particles, not sufficiently well defined for their determination. A somewhat similar rock occurs on the north bank of Four-mile creek, which is more markedly porphyritic, its constituents being larger, and the large feldspar predominantlv orthoclase. This rock is evidently a massive eruption of very considerable extent, as it apparently forms a much larger hill west of the Sugar-loaf and large outcrops up the north branch of Four-mile creek, nearer to the Ward district. In the saddle immediately east of the Sugar-loaf is a small dike of diabase, and about half a mile east is a larger one of the same rock, the former a dense black rock, in which only small plagioclase crystals can be distinguished, the other a granular mixture of augite, feldspar, and ore particles. Both are free from oliviiie. The former has a little globulitie glassy base, while the hitter is entirely crystalline. VOL 13 5 66 PRECIOUS METALS. At Jamestown (also known as Jimtown) occurs a normal quartz-diorite of rather light color, although it contains considerable hornblende. Titanite is also abundant in this rock, and it forms a dike, running east and west, almost in the street of the town. The cliffs, over 500 feet in height near Jamestown, are formed of quartz-porphyry of a white color, which is partly due to alteration and partly to the absence of basic minerals. It is composed of pale flesh-colored orthoclase, sometimes having crystals one inch in diameter, with quartz, which is not particularly prominent, and occasionally a bleached mica. The ground-mass is micro-crystalliue, and consists almost wholly of quartz, with a few small crystals of orthoclase and plagioclase felds-par. By its appearance it should be an older rock than any of the others. It contains 67 per cent, of silica, and by assay no gold. A dike is found in the Ward district which contains pyrites, a ,! is supposed to be a continuation of one of those in the Sugar-loaf district; but as no specimens were obtained, its determination could not be made. Still another dike, called the Black Eagle, south of Sugar-loaf, is said to have been traced 16 miles in an east and west direction. MINES. The mines of Boulder county are chiefly noted for the occurrence of telluricle minerals, next' to the native metals the richest and rarest ores that occur in nature. The telluride belt occupies the eastern part of the district, extending to within a short distance of the sedimentary beds on the east. Its western limit may be roughly defined by a line running from Jamestown west of Gold Hill and through the Sugar-loaf. It comprises, as already stated, the Magnolia, Sugar-loaf, Central, and Sunshine districts. West of these it is said that no tellurides have been found. In Caribou district, where the earliest discovery was made in 1869-'70, the ores are mainly argentiferous galena, and are generally quite rich. In the Ward district, at the head of Left-hand creek, the ores are largely pyritiferous, and contain, where decomposed, free gold, but are generally difficult of reduction. In the Saint Vrain, on the other hand, where comparatively small developments have been made, there are large veins rich in copper, but contain little silver. The district as a whole is characterized by exceptionally rich ores, in spite of which development has been very irregular and production uncertain. This is due in large part pvobably to the somewhat irregular manner of occurrence of the ores. The veins, which are popularly regarded as true fissure veins, and generally stand at a steep angle, are often of great width, but the rich ore, on the other hand, is concentrated in thin streaks and not very continuous bodies. If we confine the term true fissure vein to its narrowest limits, and apply it only to that form of vein which was once evidently a strong, deep-seated, open fissure that has been filled in by vein matter and ore foreign and distinct from the country rock, there are probably no true fissure veins in this district. As far as known, the vein material is almost without exception an altei-ation of the country rock, which is impregnated with rich mineral. This impregnation has taken place either along the contact of a porphyry body with the country rock or in a pre-existing vein of pegmatite, or again 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 in general between northeast and northwest, but in Ward district an east and west direction seems to prevail. Their plane, as already stated, stands at a high angle, approaching the vertical. Placers have been worked at various points in the narrow valleys which intersect the districts. Though rich, their superficial extent cannot be great, and no data have been gathered in regard to them. MINERALS. No exhaustive miueralogical study has yet been made of this interesting region. Among such rare deposits the temptation to discover new species is great, and it is necessary to accept with caution the statements as to their occurrence. In the list below the attempt has been made to give as complete as possible an enumeration of the unusual minerals occurring here under the following categories : I. Tellurides . Old species proved to occur, and cited by standard works on mineralogy ; b. New species recognized by standard works on mineralogy ; c. New species, probably good, but needing further investigation ; d. Mixtures described as species. II. Other minerals mentioned which have not been confirmed by publication or analyses. The occurrence of those marked with an asterisk is doubtful either as a species or in point of occurrence, and needs further investigation. I. Tellurides a. Old species proved in Boulder county: Altaite (PbTe) ; anal, by Genth. (Cited by Dana and Naumauu-Zirkel). Hessite (Ag 2 Te); anal, by Geiith. Hessite, auriferous=petzite. Genth; not indep. sp. Sylvanite (AgTe 2 + AuTe 2 ) ; anal, by Geuth. Cited by D. & Z. Tellurite (TeO 2 ) ; anal, by Genth. Cited by D. & Z. Tellurium, native, Geuth. Cited by D. & Z. b. New species recognized : Calaverite [M(AuTe) 2 +AgTe 2 ], sp. by Genth, from Calaveras co., Cal. Cited by D. & Z., sometimes regarded as a variety of sylvanite. Coloradoite (HgTe), sp. nov. by Genth. Cited by D. & Z., orig. from Boulder co. Schirmerite [3(Ag 2 Pb) S+2(Bi 2 S 3 )], sp. nov. by Geuth. Cited by D. Groth and Z. A mineral of the same name by Endlich, from the same locality, is pronounced a mixture. Orig. from Boulder co. GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 67 c. New species needing further investigation : Ferro-tellurite (FeTeO 4 ), sp. nov. Genth. Mentioned by Groth. Orig. from Boulder co. Magnolite (Hg 2 TeO 4 ), sp. nov. by Genth. Orig. from Magnolia district; decomposition product of coloradoite mentioned by Groth. d. Mixtures described as species : Heuryite, Eudlich. Universally pronounced a mixture. Lionite, sp. uov. by Berdell. Considered impure tellurium by Dana (App. Ill, p. 119). Tellnre-pyrite, J. A. Smith. Descr. by C. U. Sheppard ; from description, probably a mixture. e. Menorite (Ni 2 Te 3 ), sp. uov. by Genth. Orig. from California. No anal. Smith authority for Boulder co. II. Other minerals mentioned: *Amalgam. Authority, Smith. Argeutite. Authority, Smith. *Bismuth, native, sulphide, and carbonate. Smith. Copper, native, minute crystals. Smith. *Iodyrite. Endlich. *Kobellite. Smith. Sp. not recognized in Dana. Mercury. Smith. *Pyrargyrite. Eudlich. Roscoelite. Sp. uov. Genth. Eoscoe believes it a mixture. CENTRAL DISTRICT. The most prominent mine in this district is the Golden Age, near Jamestown. It is on the contact of porphyry with the Archaean, the former constituting the hanging wall. The vein is about 40 feet in width. The richest ore conies from a streak of white quartz from 1 to 2 feet thick on the foot wall, which is sometimes almost a mass of free gold. Pyrites prevail toward the hanging wall, but small rich concentrations of gold are also found at intervals. GOLD HILL DISTRICT. This is in the telluride belt, and is traversed by the Hoosier gangue. Many of the telluride veins cross the Hoosier gangue, and are said to be richer in its neighborhood. The most prominent among these are Cold Spring and Goldsmith Maid. The Red Cloud is the oldest mine in the district, and is the one in which tellurides were first discovered in 1872. Its vein is 3.J feet in width, and the ore was telltmdes at the surface and auriferous pyrites iu depth. The Slide, Melviua, and Prussian are also important deposits. The Emancipation is near the Sunshine district. All these ore in the granite-gneiss, which here offers but few good exposures. The Washington Avenue mine, west of Gold Hill, carries galena, blende, and pyrites. SUNSHINE DISTRICT. This district comprises the easternmost development of the telluride belt. Its ores are generally of lower grade, free gold and tellurides occurring in the upper portion, passing into pyritiferous ores in depth. Prominent mines are the American, Grand View, Sunshine, Osceola, and Young America. SUGAR LOAF DISTRICT. In this district the Yellow Pine mine is an enrichment of the Hoosier gangue of pegmatitic granite. Other prominent mines are Baife's lode and the Emerson, both carrying telluride in granite- gneiss. MAGNOLIA DISTRICT. This is at present the southern limit of the telluride line. Here, as well as in the neighborhood of Jamestown, the gueissic character of the country rock is very distinct, and the bedding planes are easily distinguishable. The prevailing strike seems to be in a northeasterly direction, which is also that of most of the veins of the telluride belt. The Senator Hill is one of the most promising mines of the district. In the Keystone and Mountain Lion, which are said to be on the same vein, a narrow deposit only from 6 to 7 inches in width, the new mineral coloradoite is found. WARD DISTRICT. Between Gold Hill and Ward the gneiss is much contorted and the bedding very plain, and bodies of eruptive rock, which were comparatively wanting in the telluride belt, are here frequent. The most important mines are the Niwot, Columbia, and Stoughton. The ores are sulphides of iron and copper, carrying gold, and therefore, when undecomposed, difficult to reduce. CARIBOU OR GRAND ISLAND DISTRICT is situated at an elevation of nearly 10,000 feet above sea-level. Its most important mine is the Caribou, which was discovered in 1869. and has produced a very large amount of silver ore. This is a massive mixture of galena, chalcopyrite, and ziucblende, which occurs in gneiss, but closely associated with diabase. Other important mines are the No Name (which is said to cross the Caribou and fault it), the Boulder County, and Native Silver. The ores of this district are essentially silver-bearing, but also carry some gold. 68 PRECIOUS METALS. Mine. Country rock and vein. Ore and gangnc. CENTRAL DISTRICT. Goldeu Age (near Jamestown) Smuggler GOLD HILL DISTRICT. American Cold Spring MAGNOLIA DISTRICT. Keystone Mountain Lion WAKD DISTRICT. Nelson. Niwot.. SUGAR-LOAF DISTRICT. Emerson Yellow Pine Bailo's lode GRAND ISLAND DISTRICT. Boulder County ; Caribou .' Horsefall lode Native Silver . . . Foot wall aneiss; hanging wall porphyry . Vein vertical; strike, E. and W. ; dip, 44 ; 40 feet wide. Mica-schist. Strike, N. and S.; dip, 60 E Granite-gneiss. Strike, NE. ; dip, 84 SE. No specimens. From the gangue it is apparently fine-grained granite, and a much-altered porphyry is near by. Gneiss. No specimens. Vein : dip, 65 ; 2 feet wide Gneiss. Vein : strike, NE. ; dip, 65 ; 2 feet wide Decomposed mica-schist. Strike, NE. ; dip, 62. Granite-gneiss hanging wall and porphyry foot wall. Strike, E. andW. ; dip, 70 N. Altered gneiss Granite, with reddish feldspars and but little mica. Coarse granite-gneiss with red feldspars, in which are veins of fine-grained biotite-grauite. Vein: strike, E. and W. ; dip, 55 N Syenitic gneiss. Diabase occurs in the neighborhood. Vein : strike, E. and W. ; dip, 14 N. (76 ?) Mica-schist. No specimen. Strike, E. and W. ; dip, 85 If A fine-grained biotite-granitc. Near the vein the biotite has dis- appeared. Vein: strike, E. and W. ; dip, 5 N. (85?) Free gold, with iron and copper pyrites and quartz. Tellnrides and pyrites in siliceous gangue and altered country. Tellnrides of gold, silver, and mercury, with free gold, sul- phide of iron, zinc, lead, and copper; no specimens. Tellurides. Specimen, evidently from the side of the vein, is attrition material ; clay, rounded pieces of quartz, with py- rites and Jellurides. Tellnrides in quartz gangue. No specimens. Iron oxide and free gold, with tellnrides. Gangue : quartz and feldspar. Anriferons chalcopyrite and pyrite with free gold. Gangue: quartz and altered country. Massive pyrite and chalcopyrite cemented by quartz. The same rock impregnated with fine grains of pyrite and tel- lurides. Gray copper, azurite, malachite, and some unknown greenish mineral in a decomposed gneiss or granite. At the contact of granites is quartz with a little galena, pyrites, and black stains. Galena, pyrite, and blonde in quartz ; blende crystals covered by a layer of hematite. A massive mixture of galena, chalcopyrite, zincblende, and a mineral called "antimony". Chalcopyrito and pyrite with free gold, some galena and zinc- blende. Mixture of galena and sulphides. JEFFERSON COUNTY. This county includes the foot-hill region south of Boulder county as far as South Platte river and a narrow strip of the mountain region. Although mainly a mountain county, and surrounded by important mining districts, it reports no product of the metallic minerals. On the other hand, its production of coal from Ealston creek, Golden, and Morrison, and of valuable fire-clays and building-stone all along the foot-hill region, is extremely important. From the basaltic mesas at Golden a number of interesting zeolitic minerals have been obtained by Mr. Cross, of the United States geological survey, among which are analcite, apopliyllite, chabazite, laumontite, mesolite, natrolite, scolecite, stilbite, and thomsonite. Jet is also found in the Tertiary beds under the lava flows and bole. GILPIN COUNTY. This is the smallest county in the state, and consists of a triangular bit of mountain region, covering 180 square miles of surface, drained by the north fork of Clear creek and adjoining Jefferson county on the west. It is the oldest mining region in the state, the first gold being discovered here in Eussell gulch in 1859, and is still the greatest gold producer. Its placer deposits, lying along the bottoms of deep ravines, are of limited extent, but they are extremely rich, and though most of them have been worked over several times, they still yield a certain amount of gold. This county is entirely in the Archa3au formation, which consists mainly of gneiss, the prevailing type being structureless granite-gneiss, already described in the section on Boulder county. The gneiss is penetrated by various bodies of porphyry ; but, owing to the peculiar readiness with which the rocks yield to atmospheric influences, few characteristic outcrops are found, so that the geological structure is not readily recognized on the surface. Here also the veins are mainly alterations of the country rock along certain planes, and rarely, if ever, show the character of a pre-existing open fissure filled by foreign material. In some cases the vein material seems to be a porphyry dike. Many of the veins have been traced to a very considerable depth, in some cases to over 1,000 feet, and it is claimed that some have been traced in length between 2,000 and 3,000 feet. The direction of the veins lies either between north and south and northeast and southwest, or within 10 of east and west. Among the'more important veins the Gregory & Briggs, Bates, and a few others belong to the former, the Bobtail, Burroughs, Gnnuell, and others belonging to the latter group. In all the dip is generally near the vertical. Faulting or displacement of the vein is rare, but where the vein material is porphyry it frequently contains inclosed fragments of gneissic country rock. In one mine rounded boulders of gneiss of considerable size have been found in the vein at a depth of about 700 feet from the surface, but whether their form is due to attrition of the two walls or to the rounding action of water and mineral solutions is not known. GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 69 The ores are mainly a mixture of pyrite and chalcopyrite, with less frequently galena and zincblende. carrying more or less gold. In the northern portion of the district, however, galena ores, with zincblende and pyrite, carrying silver, occur, but as a rule contain little or no gold ; and similar deposits almost surround the extremely circumscribed limits of the gold-bearing area, whose radius, taking Central City as a center, is only about 1 miles. In the gold veins the richer ore generally occurs in streaks that are not more than one foot wide, a compact fine-grained mass of pyrite, copper pyrite being as a rule richer than the ordinary pyrite. The rest of the vein, which often attains a width of many feet, carries pyrites (irregularly disseminated through a more or less decomposed mass of country rock) either in the form of white clayey material or as a mixture of quartz and i'eldspar. Outside the narrow streaks of solid sulplmrets, the bulk of these ores, as they are extremely difficult to smelt, are generally treated by mill process, and the percentage of loss is generally much higher than in more completely oxidized ores, or those which are free from pyrites, averaging probably 40 per cent. The richer portions of the ore and concentrations of mill tailings are sent to the smelting works in the valley below. According to Mr. A. N. Eogers, of the Bobtail mine, who has had long experience in the underground workings of this district, the veins invariably follow the cleavage planes of the country rock, the planes crossing the strata with a nearly vertical dip, while the stratification of the country rock has a dip to the eastward. He also states that the porphyry has its cleavage in common with the country rock where the cleavage does not invade the veins themselves, the joints or laminae taking the line of the veins and lying parallel with their Avails. Hence he reasons that the porphyry is older than the veins, inasmuch as the cleavage is older and intersects the porphyry. These observations are of interest as giving a slight indication of the age of deposits in the Archoeau, for which, as a rule, it is impossible to obtain any definite data. The mountain region, from 12 to 15 miles in width between the mining districts and the plains, mainly included in Jefferson county, which consists also of Archrean rocks, has hitherto proved relatively barren of valuable minerals. In this region the rocks are comparatively unclecomposed and the bedding planes remarkably distinct, having a prevailing easterly dip. They are generally gueissic in character, with some granite, and, as a rule, are highly siliceous. \ MINERALS. Besides the ordinary sulphides of iron, copper, zinc, and lead, sulphides and arsenides of silver are found ; and among rarer minerals the occurrence of enargite (sulphide of copper and arsenic) in massive crystals in the Powers mine, in Eussell district, is noteworthy. From the Wood mine, in Leavenworth gulch, a small pocket of pitchblende or uraninite was obtained by Mr. Eichard Pearce, who first noticed it in the refuse of the dump. Aurichalcite is reported by Dr. Genth in connection with zinc minerals, cobellite by Dr. Loew, and melaconite by Dr. Peters with copper minerals. The following minerals are reported from this county by J. Alden Smith and Dr. Endlich, but no analyses are given : Allophane, azurite, calamine, chalcanthite, cerargyrite, copper (native), garnet, gold (in crystals), goslarite, greeuockite, jarosite, lievrite, maguesite, magnetite, magnetic pyrite, marcasite, mispickel, molybdenite, selenium, siderite, smithsouite, sulphur (native), tourmaline, willemite, wolfeuite, zincite, and a variety of uranium minerals. MINING DISTRICTS. The mining districts, like the county, are extremely small, and their limits not definitely known. The Gregory district includes the mines in the immediate vicinity of Black Hawk and Central, the most important being the Bobtail, which is the richest and largest producer, although worked on a length of only 800 feet. On the Gregory lode claims have been located over a length of 4,500 feet, but actual explorations cover an extent much less than half of this. It is expected that these two lodes, together with the Bates (which lies to the northwest of the Gregory and nearly parallel to it), whose courses are convergent, will all unite to the southward in the Mammoth lode. Xevada district, which lies to the west of the Gregory, takes in the head of Nevada gulch, and includes the California, Kansas, Burroughs, and other lodes. The Kussell district lies to the south of these, in Kussell gulch. The number of mines is too "great to admit of any special mention, but the folio winji table gives the data furnished by specimens collected by the census experts: Mine. Country rock and remarks. Ore and gangne. NEVAKA DISTBICT. American Flag . California.. Hidden Treasure . Gneiss rich in biotite Galena, copper, and iron pyrites, and some zincblende, cemented by quartz. Granite-gneiss impregnated with pyrite. A dike of quartz-por- Pyrite. ehalcopyrite. zincblende. and galena, with siliceous pliyry 2 feet tliiek on tbe hanging wall. cement ; in some portions gray copper. Same walls as in the California mine Chalcopyrite and dark blende. Gangne : altered country rock. Jones Fine-grained granite Dark blende, with pyrite. and some chalcopyrite. In one case t In se are deposited on both sides of a thin fragment of granite- gneiss. Kansas Biotite-gneiss ; fresh on foot wall, altered on hanging wall Fiue-grained mixture of pyrite, ehalcopyrit, and fahlerz. Bennett's Kansas Li<;lit granite-gneiss Fine-grained mixture of pyrite and chalcopyrite. with siliceous cement, associated with fragments of wall-iv Kent County Lacrosse (liurroughs). Pyrenees Polk County. Gneiss. On the hanging wall dark blende concentrated in the Pyrite, chalcopyrite, galena, and dark zincblende. with quartz fissures. ; cement. Fine-grained biotite-gneiss Pyrite, with fragments of decomposed wall-rock. Dark gneiss rich in biotite Massive galena, with chalcopyrite and pyrite: also fragments of wall-rock cemented by blende and pyrite. Hanging wall fine dark mica-schist Chalcnpviite. with some pyrite cementing frugmema of gneiss. 70 PRECIOUS METALS. Mine. Country rock and remarks. Ore and gangue. NEVADA DISTRICT continued. Fragments of wall-rock with a little pyrite, or massive pyrito with siliceous cement. Pyrite and chalcopyrite, with quartz. Coarse pegmatite impregnated with galena, pyrite, and chalco- pyrite. Chalcopyrite, with some pyrite, cemented by quartz. Quartz and pyrite. Chalcopyrite and pyrite in altered country rock. Pyrite and chalcopyrite with quartz. Porphyry heavily impregnated with pyrite. (Massive mixture of pyrite, chalcopyrite, zincblende, and galena. t Gangue: altered country. Pyrite and chalcopyrite. Gangne : altered country. Mixture of pyrite and fluorito; galena and falilerz occasionally present. Massive enargite, with pyrite and fluorite. Enargite, fahlerz, and pyrite. Gangue: feldspar and quartz. Pyrite. Gangue : quartz and feldspar. Mixture of galena, blende, chalcopyrite, and occasional ruby sil- ver. Gangue rock : white porphyry. Decomposed granite, in which cerussite and chlorides have been deposited. Pyrite, with copper and arsenical pyrites and zincblende. Gangue: quartz and feldspar. Massive galena, with some cerussite and zincblende. Gangue: bleached and kaolinized country rock. Massive chalcopyrite and pyrite. Gangue: altered country rock. Cerussite ; alteration products of galena, with stains of copper. Gangue : altered country rock. West Flack Forks GREGORY DISTRICT. Bobtail Fine-grained compact granite-gneiss, partly schistose on the foot wall. Cashier Gneiss Minnie Felsite-porphyry impregnated with pyrite, and carrying frag- ments of Archaean rocks. Gneiss Smith ) Wain J EUSSKLL DISTRICT. i ENTERPRISE AND MOUNTAIN- HOUSE DISTRICT. Granite. Altered porphyry occurs at 70 feet distance ILLINOIS CENTRAL DISTRICT. IIAWKEYE DISTRICT. Hard Money Altered gneiss EUREKA .DISTRICT. QUARTZ VALLEY DISTRICT. CLEAR CREEK COUNTY. Clear Creek county lies to the south of Gilpin, and is considerably larger than the latter, having an area of 460 square miles. It extends from the western boundary of Jefferson county to the crest of the Colorado range, and is, next to Lake county, the largest producer of silver in the state. Its mines lie mainly among the steep rocky spurs between the various tributaries of the main Clear creek, but it includes also the Geneva district across the divide on the south, at the head of the Geneva creek, a tributary of the South Platte. Like Gilpin county, this county lies in the Archaean formation, the rocks being mainly gneissic, with subordinate development of granite. Porphyry dikes seem much more frequent than in Gilpin county, but this may be due in part to the steepness of the mountain slopes, on which the character of the country rock is more readily distinguished. The veins, like those of Gilpin county, seem to be mainly alterations of the country rock along a jointing or fan! t- plane, and are frequently in direct connection with the porphyry dikes, which form either one of the walls or constitute the vein material itself. In some cases also the vein seems to be an impregnation of a pre-existing pegmatite vein in the gneiss. MINERALS. The ores of Clear Creek county are essentially silver-bearing, the silver being derived from argentiferous galena, and in part from fahlores. In the eastern or lower portion of the district, where the earliest developments were made, the ores are, however, mostly pyritiferous, and contain relatively little galena, hence yield both silver and gold. In the upper districts, around Georgetown, they are mainly silver-bearing. The rich ores are smelted directly, and are generally sent out of the district for this purpose. A very considerable proportion of the product is, however, concentration ore, which is generally an impregnation of the country rock at a greater or less distance from the main crevice. This impregnation seems to take place by preference on one side of the vein, and this is generally the foot wall. These ores are concentrated, as a rule, in Georgetown, and the concentrates are sold to smelters. A relatively small proportion of the oxidized portion of the deposits, especially those which are comparatively free from lead and zinc, are suitable for milling. There is no doubt that this district contains an unusually large proportion of valuable veins ; but their development has been incommensurate with the intrinsic value of the deposits for various reasons, among which are pernicious systems of working and the abundant cases GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 71 of litigation arising from the close vicinity of the veins to each other and their frequent crossings. A very large proportion of the more important mines were closed at the date of visit, and consequently the returns obtained by the expert are far from complete. Under these circumstances it were useless to attempt to form any generalizations on the direction or interdependence of the veins as a whole. Besides the ordinary metallic sulphurets, the following minerals are reported as occurring in the county: Anglesite, argentite, azurite, bornite, bournonite, calamine, caledonite, chrysocolla, fahlerz, garnet, minium, proustite, psilomelane, pyromorphite, silver (native), stephanite, sternbergite, stibnite, tennantite, tetrahedrite. The following table gives the character of ore and country rock of the mines from which specimens were obtained : Mine. Country rock and remarks. Ore and gangue. BANNER DISTRICT. First National... Big Chief. Nathan . . . Mica-gneiss; finely bedded on hanging wall; iron-stained and schis- tose on foot wall. Mica-gneiss, containing on the foot wall a number of small pink garnets. Gneiss CASCADE DISTRICT. Muscovite CORRAL AND TRAIL BUN DIS- TRICT. Donaldson . Brooklyn GENEVA DISTRICT. Baltic GRIFFITH DISTRICT. Burleigh Consolidated Hercules. Diamond Dunderberg Equator Junction Colorado Central IDAHO DISTRICT. Champion Gem Idaho tunnel. Victor... Mackey. MONTANA DISTRICT. Free American . Murray Joe Reynolds... HOHBIS DISTRICT. Albro Alexander. Eagle BEATON DISTRICT. Tropic. SPANISH BAB DISTRICT. Fairmoun t-Shafter Freeland. Hukill Mayflower. Hanging wall granite-gneiss ; foot wall decomposed gneiss and felsite-porphyry. Hanging wall iron-stained gneiss; foot wall grayish compact felsite. Gneiss . No specimen. Gneiss, passing on one side into granite ; on the other, into schists Porphyry and gneiss (a) . Altered gneiss Indistinctly bedded gneiss. IOWA DISTRICT. Hanging wall mainly white orthoclase ; foot wall gneiss. Gneiss indistinctly bedded Gneiss . No specimen White granite whose mica is altered to a light greenish substance Foot wall mica-gneiss ; hanging wall pegmatite vein Quartz, stained reddish and yellow by iron oxide. Pyrite, chalcopyrite, fahlerz, and chalcosite. with quartz matrix. Gangne : altered gneiss. Crumbling iron-stained mass with no recognizable minerals; probably altered country rock. Stained breccia-like mass, with no distinct metallic minerals visible. Pyrite in quartz ; smelting ore contains fahlerz ; pyrite thoroughly decomposed constitutes free-gold ore. Gangne: altered gneiss. Pyrite and chalcopyrite with fahlerz. Gangne : quartz and feld- spar. Pyrite, chalcopyrite, blende, fahlerz, and a little galena in siliceous 'gangne ; occasional pink calcite crystals. Chiefly massive galena and chalcopyrite. Chalcopyrite and argentiferous galena. Chalcopyrite and blende. Milling ore : altered country rock im- pregnated with particles of pyrite. Arsenical fahlerz with aznrite and malachite. Gangne : altered country rock. Galena, zincblende, and pyrite deposited on hanging wall rock. Zincblende, pvrite, etc., altered in high grade ore to a stained decomposed mass. Gangne : altered country rock. Ore and gangue specimens both granite-gneiss, the gangue specimen having more visible pyrite than the pay ore. Galena, pyrite, and barite. Galena, pyrite, and chalcopyrite. Gangne: altered country rock. Galena. Gangue: quartz and feldspar. Gneiss. Gneiss . Gneiss . Gneiss impregnated on foot wall with pyrites. Pyrite, chalcopyrite with some fahlerz. Gangne: quartz and feldspar. Galena, pyrite, chalcopyrite, and possibly fahlerz. Gangne: quartz and feldspar. Seems to be mainly country rock impregnated with chalcopyrite and other minerals invisible to the eye. Brilliant mass of zincblende, with galena, fahlerz. and pyrite ; concentration ore wall-rock more or less impregnated with these minerals and carrying calcite. Galena, pyrito, and pyrolusite. Gangne: feldspar in large in- dividuals. Fine-grained mixture of pyrite and chalcopyrite ; relative rich- uessdependingonproportionof latter. Gangne: altered country rock. Much decomposed gneiss Pyrite and bornite in siliceous gangue. Schistose gneiss of varying character Pyrite and galena, with some fahlerz and zincblende either mas- sive or mixed with siliceous gangne. Gangne: altered country rock. a Porphyry assays 0.033 to 0.083 ounce of silver per ton, with a trace of gold. Gneiss impregnated with pyrites more abundantly on the foot wall. Gneiss varying in depth from a hornblendic variety to a feld- spathic. 72 PRECIOUS METALS. Mine. Country rock and remarks. Ore and gangne. UPPER UNION DISTRICT. Chiefly massive chalcopyrite. Massive galena, chalcopyrite, and pyrite, with a little fahlerz. Gangue : altered country rock. Rich ore, pyrite in quartz ; second-class ore, gneiss impregnated with pyrites. Pyrite with a little galena in quartz ; low-grade ore, gneiss im- pregnated with pyrites. Galena and zinchlende. Gangue: altered country rock. Neith VIRGINIA DISTRICT. Lake TORK DISTRICT. Clifford SUMMIT COUNTY. By the recent cession of the lands of the Ute reservation a large area of the mesa region of the Colorado plateau country between the White and Grand rivers, extending as far west as the boundary of Utah, has been added to what was originally a small mountain county. This new region, with the exception of the White Eiver plateau, at the head of the White river, in which Palaeozoic rocks, cut through and partially covered by basalts, are exposed, is mainly covered by Tertiary beds, and offers little prospect of metallic wealth. As originally constituted, the eastern end of Summit county adjoins Clear Creek and Park counties, the crest of the Colorado range separating it from the former, and the cross range connecting this with the Mosquito range and dividing the two parks from the latter, and includes a portion of the Park range, consisting of the northern end of the Mosquito range and the Gore mountains, together with the valleys of the Blue river on the east of these mountains, and of Eagle river on the west. The high mountain portion of the county is mainly composed of Archaean rocks, but along the valley of the Blue there are fragmentary beds of Mesozoic and Palaeozoic rocks which have escaped erosion, relics of a former connection of the Mesozoic seas which filled the South and Middle parks. These rest on the Archaean of the Park range, and are repeated on its west side, the Park range probably having been lifted up by the great fault movement which is so well denned in the Mosquito range. Along the upper portion of Eagle river there are Palaeozoic beds dipping north and resting on the Archaean of the northern end of the Sawatch, which, as one goes westward down the stream, gradually pass under the succeeding higher Mesozoic beds, and are finally lost under the Tertiary of the lower Grand and White rivers. Associated with the lower beds is a very considerable development of Secondary eruptive rocks, which are very inadequately represented on the existing geological maps of this region. The lofty mountain crests which bound the county on the east have hitherto been a serious barrier to the development of its ores, which, though frequently occurring in large masses, are on the average of low grade, and cannot support heavy freight or reduction charges. The recent advent into the valley of the Blue river at Frisco of the Denver and Rio Grande road promises to ameliorate this condition of things to a limited extent; but its circuitous course, which necessitates the carrying of freight from here to Denver over five times the actual distance in a straight line, still involves relatively high freigh: charges on supplies and ore. In this county there is a marked connection between the prevalence of eruptive rocks of Secondary or Mesozoic age and the richness and magnitude of the ore deposits. These are not only found in the Archaean and Palaeozoic systems, but also extend up as high as the Trias. As yet none of value are known to occur in the Jurassic or Cretaceous formations. MINING DISTRICTS. The oldest mining districts are those in the neighborhood of Montezuma and Peru, near the head of Little Snake river, the east fork of the Blue, their veins belonging to the same mineral belt as those of Georgetown, in Clear Creek county, and of Geneva gulch and Hall valley, in Park county, from which they are respectively separated only by the intervening curving crest of the Colorado range. The deposits occur in the Archaean rocks, and consist mainly of argentiferous galena and sulphurets. Several presumably valuable mines have been developed in the district, and small smelting works have been erected, with the usual want of success attendant on small capital and a limited supply of ore. No report was furnished from this district. "Numerous ore bodies have been found at the head of the Blue river, where the Palaeozoic and Triassic formations have been extensively traversed by intrusive sheets of Secondary eruptive rocks. These eruptions have undoubtedly caused considerable local metamorphism of the sedimentary beds, which have farther been extensively dislocated by a complicated system of faults, so that, without a careful study in the field, it is impossible to definitely determine the geological horizon of any individual deposit. The principal developments have taken place near Breckenridge. on the northwestern slopes of mounts Hamilton and Guyot. Reports are at hand from the Helen mine, in the Bevan district, in French gulch, whose ore body is an impregnation of quartzite, called a vein, striking NNE. and dipping 60 to the southward, and some 45 feet in width. The ore is free gold, with some silver in a quartzite, iron-stained by the leaching out of the pyrites which it originally contained. GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 73 In the McKay district the Naperville mine has a deposit of argentiferous galena and carbonates occurring between an overlying porphyry and an unreported sedimentary bed below. The Monte Cristo mine, on the slope of Quandary peak, west of the upper valley of the Blue, is a deposit of low-grade galena, with some zincblende impregnating the Cambrian quartzite. This deposit is exceptionally favorably situated for mining, the quartzite bed in which it occurs dipping eastward at the same angle as the spur of the mountain, and the overlying white limestone and succeeding rocks above having been eroded off so that it forms the actual surface of the hill and can be quarried out. In spite of its low tenor in silver, said to average 15 ounces to the ton, it seems that under proper management the mine ought to be made to pay. Veins have been discovered at many points in the Archaean rocks that form the sharp crest of the Mosquito range, often in the most inaccessible localities ; but during the census year, so far as could be discovered, none were in the condition of producing mines. Ten-mile district, between the heads of Ten-mile creek, a fork of the Blue nver,and of Eagle river, is at present the most important mining region of the county. The ores occur mainly in the Upper Carboniferous limestones and in the sandstone beds immediately above them. These lie at the western foot of the Archa3an mass which forms the sharp, jagged crest of the Mosquito range, and which has been lifted tip by the movement of the great Mosquito fault. An area here of some 10 miles square has been the scene of most wonderful eruptive activity during or at the close of the Mesozoic epoch. In number and size the intrusive bodies of porphyry and porphyrite which occur in these sedimentary formations, either as iuterbedded sheets, as dikes, or as intermediate irregularly transverse bodies, exceed even those of the neighboring region of Leadville. Between these two districts, but nearer that of Ten-mile, occurs a Tertiary eruptive mass of the rather uncommon rock nevadite, or crystalline rhyolite. Although but a portion of the probable ore-bearing area has yet been prospected, the quantity of metallic minerals found here is remarkable. Unfortunately for the prosperity of the district their quality is not so satisfactory, as they mostly run very low in silver and are extremely refractory, consisting mainly of pyrites, with a very considerable admixture of zincblende. The ore deposits mostly occur in the thin beds of limestone, which are prevalent in this formation, at or near their contact with an overlying micaceous sandstone. Less frequently they are found in actual contact with an intrusive bed of porphyry, and at other times impregnating a dike of porphyry which traverses the sedimentary formations. The most important and the typical mine of the district is the Robinson. Its ore is an argentiferous galena of exceptionally high grade, associated with pyrites and some zincblende. It occurs at or near the surface of a bed of bluish-gray limestone, overlaid by a white micaceous limestone, dipping northward at an angle of about 17. The ore seems to be an actual replacement of the country rock. The upper layer, locally called " white iron", which is a mixture of fine-grained crumbling pyrites with white mica, nearly free from galena, seems to be a replacement of a portion of the overlying sandstone, and is practically worthless. Below this the ore consists of a varying mixture of galena and pyrites, exteading at irregular depths- into the limestone, and in the larger bodies occupying nearly its whole thickness. The ore chute, whose maximum width is 100 feet, has been traced over a linear extent of 1,000 feet, following the general direction of the dip. A line of fracture, probably a fault-plane, may be observed in the roof following the line of the ore body, i. e., a vertical plane at right angles to the line of strike. It seems probable that this fault-plane furnished the channel through which the ore solutions reached the limestone, inasmuch as pyrites extend apparently into the fissure as far as it has been opened, and in the portions of the limestone adjoining there is no mineral matter at its contact with the overlying sandstone at a little distance from the ore body. Small bodies of mineral have also been found in the limestone along the line of several minor fault-planes, which are also at right angles to the line of strike, and whose displacement amounts at most to a few feet. The Wheel of Fortune, on the summit of Sheep mountain, at the foot of which the Eobinson mine stands, has an extremely rich body of silver ore in the same or an adjacent .limestone stratum and adjoining an irregular transverse body of white porphyry. On Elk mountain ore occurs over a very large area in a thin bed of limestone at a higher horizon than that of the Eobinson. This ore is a similar mixtureof pyrites and galena, oxidized near the surface, andsometimes to considerable depths along certain lines, with unaltered sulphurets on either side. This almost continuous body has been developed by the adjoining claims of the White Quail, Aftermath, Milo, Badger, Raven, Eagle, and Colonel Sellers to an extent of over 2,000 feet along the strike and 700 to 800 feet on the dip. While a great portion of this immense mass is too poor in silver to pay for working, as an instance of widely extended ore deposition it is certainly remarkable. Where the same bed crosses the north end of Sheep mountain, a mile or two to the eastward, beyond an intervening gulch, similar great bodies of pyritiferous ores, with more or less argentiferous galena, are found in the Snowbank, Xettie B., Triangle, and other mines. Ore is found following the limestone horizons at higher levels and extending probably up into the Triassic formation. In one portion of the district, called Copper mountain, copper minerals ae associated to some extent with the iron pyrites. The Pride of the West, on Jacque mountain, is a type of the deposits which follow a narrow dike of porphyry. Here the vein mass, which is from 6 to 30 feet in thickness, crosses the formation diagonally and stands nearly vertical. It is an iron-stained quartzose mass, through which run seams or veins of barite parallel with the 74 PRECIOUS METALS. walls, one being particularly persistent, and in connection with which the richest mineral is found. Where the siliceous gangue material is sufficiently unaltered it is found to be a decomposed quartz-porphyry. Another example of the type is the Little Chicago, which follows a dike of decomposed porphyry. This vein or dike yields an abundant supply of water, which is milky, from suspended particles of kaolin. Small jets of water from the adjoining rock also deposit hydrated oxide of iron, but the bodies of mineral as yet developed have been small and at widely separated intervals. On Eagle river, in the neighborhood of Bed Cliff, deposits of argentiferous galena and cerussite, associated with iron oxides., are also found in limestone, sometimes between it and an overlying white porphyry, and again with a limestone hanging wall and a quartzite foot wall. These limestone beds belong to the Paleozoic system, and are probably Carboniferous in age; but whether, like those of Ten-mile, they are in the upper portion of the Carboniferous, or, like those of Leadville, in the lower, is not known, nor is it of any practical importance. They are said to be very much broken and faulted. This district, as well as that of Ten-mile, is now reached by the Denver and Bio Grande railroad, and its ores are treated at Leadville or by some of the smelters on the plains. PARK COUNTY. Park county embraces the broad mountain valley of the South park, its boundary running along the crest of the Mosquito range on the west, and of the irregular chain which separates it from the Middle park on the northwest. It includes also, on the northeast, a portion of the Colorado range lying to the south of Clear Creek and to the west of Jefferson county. The valley plains are covered by sedimentary deposits of Mesozoic age, which, with underlying and conformable Palfeozoic formations, slope up to the crest of the Mosquito range on the west, but are cut off abruptly against the Archaean on the east, probably by a fault. The coal beds of the Upper Cretaceous are thus included in this area, and have been extensively developed in the neighborhood of Como. Near Hamilton there are deposits of hematite iron ore, whose exact geological horizon is not known, and which have been but irregularly developed. Besides the less precious minerals, there are salt springs in the southern portion of the park, from which at one time rock-salt was obtained, and which probably originated in deposits of this mineral in the Triassic rocks. There are also indications of copper in the sandstones of the Trias, in the form, usual in these strata, of impregnations of carbonate of copper accompanying plant remains. As yet none have been discovered of economic value. Minerals carrying the precious metals have thus far been developed only in the Palaeozoic formations, with their accompanying porphyries of Mesozoic age, and in the underlying Archaean. In the northeastern corner of the county are the Hall Valley and the Geneva districts, whose deposits properly form part of the Clear Creek belt of silver-bearing ores and occur in the same gneissic formation. The Whale lode, in the latter district, is one of the most characteristic. The country rock is here a fine-grained gneiss, with a general strike of north and south and a steep dip to the west. It is intersected by numerous veins of pegmatite composed largely of feldspar. The lode itself runs northeast and southwest, dipping to the northwest at an angle of 65, and is a thin vein, consisting mostly of barite, carrying also fluorite and quartz, with irregular bunches of galena and gray copper, and often separated from the adjoining portions of the lode by a clay gouge. This vein varies from an inch to 3 feet in thickness. The crevice of the lode is between 5 and 10 feet in width, and outside the above-mentioned vein consists of altered gneiss, more or less impregnated with pyrite, galena, zincbleude, and a decomposition product. The pyrite is said to be confined to the decomposed wall-rock, and seldom occurs in the vein proper. There are numerous other veins in the vicinity of this lode which are also characterized by the occurrence of barite as gangue material. The Treasure Vault is said to have produced bismuth-silver ore. The principal mineral developments of the county have taken place along the eastern slopes of the Mosquito range, and have been mainly derived from Palaeozoic rocks, since, although numerous small deposits of gold and silver have been found in the underlying Archaean, which is exposed near the crest of the range and in the deeper canons, and many interesting minerals have been obtained from them, no ore deposits of considerable value have yet been found in this formation. The Palaeozoic system here consists of the following series, commencing at the bottom: Feet. Cambrian quartzite .- 200 Silurian or White limestone 200 Lower Carboniferous or Blue limestone 200 Middle Carboniferous or Weber grits 2, 000 to 2, 500 Upper Carboniferous, consisting of limestones, sandstones, and conglomerates 1,000 to 1,500 These formations, as well as the underlying Archaean, have been traversed by eruptive rocks of Secondary age, mainly quartz-porphyries and porphyrites, which, in the Archaean, occur generally in the form of irregular dikes, but in the Palaeozoic system are mainly spread out in intrusive sheets between the beds. There is a marked connection between the prevalence of these eruptive masses and the development of mineral deposits. Indeed, in many cases here, as in the Leadville region, it is evident that the ore bodies are a concentration of the metallic minerals originally disseminated through the masses of these bodies and now deposited along their plane of contact with the sedimentary beds, and extending more or less into the mass of the latter. The type of these deposits may be found in mounts Lincoln and Bross, where most valuable and extensive ore bodies have been developed in the Moose, Bussia, Hiawatha, and GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 75 other iiiiiies, which enjoy the further distinction of being the most elevated mines in the country, their altitude varying from 13,000 to 14,000 feet. The ores are mainly argentiferous galena and its products of decomposition, carbonate and sulphate of lead and chloride of silver. Barite is a frequent gangue material in the richest portion of the deposit. Pyrite also occurs with the ore, but is generally decomposed and changed to a hydrated oxide, associated with more or less oxide of manganese. These give to the mass of the ore, which frequently contains considerable mechanical admixture of clay, a red or yellow, or, where manganese predominates, a black color.. The deposits occur in irregular bodies, often of great size, in the blue limestone, and generally near its upper surface. This blue limestone now forms the surface of the spurs of the mountain, sloping east at an angle of from 10 to 15, but was origiually covered by a sheet of quartz-porphyry, portions of which still remain on the highest parts of the peak. This quartz-porphyry, to which the local name of Lincoln porphyry has been given, is of a type so widespread throughout Colorado, and seems to be so intimately connected with the rich mineral deposits, that it is worthy of a detailed description. It is so thoroughly crystalline that it is often mistaken for granite. Its most striking, although not absolutely essential characteristic, is the occurrence of large porphyritic crystals of orthoclase Of rather glassy appearance, with extremely well-defined faces, either in single crystals or Carlsbad twins, in size from a half inch to 2 inches in length. The ground mass is a crystalline mixture of two feldspars, in which plagioclase sometimes predominates, with mica or hornblende generally somewhat decomposed, and frequently a large amount of free quartz in double-pointed hexagonal pyramids, which often have the appearance of rouuded grains. The quartz often has a pink tinge. The rock itself, taken comparatively fresh, is of greenish-gray color, but often bleached by decomposition or weathering. As to the age of the porphyry in this region, it can only be said that it is later than the Trias ; but what is apparently the same rock is found in the Gunnison region, and between the Xorth and Middle parks, breaking through the Cretaceous strata. It is, however, distinctly older than, and of a different character from, the Tertiary eruptive rocks. The Dolly Varden mine of Mount Bross is a similar deposit of slightly different type. Its ore, which is mineralogically similar, occurs in the mass of the limestone in close proximity to a vertical dike of white quartz porphyry. The dolomitic limestone in which it occurs is the same as that in which the previously described deposits are found : and the ore has been traced to a vertical depth of over 100 feet, and in bodies extending from 40 to 50 feet on one side of the dike in the mass of the limestone. On Loveland hill, a spur next south of mounts Bross and Lincoln, are numerous deposits in the same blue dolomitic limestone, the best known of which is the Fanny Barrett, whose ore body stands vertically or at right angles to the stratification planes, and is probably deposited along a cross fissure or jointing plane. In Buckskin gulch, between these two mountain masses, is the oldest mine of the district, the Phillips, which is an immense mass of .auriferous pyrites, also carryuig some silver, deposited in the beds of the Cambrian quartzite near a dike of quartz-porphyry. The Criterion mine, on the north wall of the gulch, is also in the Cambrian quartzite an immense body of thoroughly oxidized material, whose original character cannot be determined, but which was probably a varying mixture of galena and pyrites, carrying both silver and gold. A porphyrite dike occurs near by. Colorado Springs mine, in the Bed amphitheater on the southwest face of Mount Bross, is a rich deposit of galena along the bedding-planes of the white limestone. Here both diorite and quartz-porphyry are- found traversing the sedimentary beds. The Sweet Home mine, near thison the cliff face, in the underlying Archaean, is principally interesting from the minerals which it has produced combinations of silver with arsenic and antimony. From the Tanner Boy, also in the Archaean, on the opposite side of the gulch, beautiful rhombic crystals of rhodochrosite are obtained. In Mosquito gulch, the Orphan Boy, once an important mine, is in quartzite underlying the limestone bed. The London mine, on London mountain, at the head of Mosquito gulch, has developed two strong veins of sulphurets, carrying both gold and silver, the one with a gangue of quartz, the other of calcite, which occur either in the Blue or White limestone in connection with an intrusive bed of White porphyry. These veins stand in an almost vertical position, as the beds in which they occur are turned up at a steep angle against the London fault, which crosses the formation diagonally, and by whose movement the Archaean rocks, which form the eastern half of London mountain, are brought up into juxtaposition with the Silurian and Carboniferous beds on its western point. Southward the masses of intrusive porphyry diminish in extent, as do also the number of developed mineral deposits. Between Horseshoe and Sacramento gulches rich bodies of galena and carbonate ore, carrying silver, have been developed in the Sacramento mine, also in the Blue limestone, to the east of the London fault, from whose surface the original covering of quartz porphyry has been denuded. On the west of the London fault the Peerless and Badger mines, the former at the very crest of the range, find their ore in the same limestone which here was covered by the White or Leadville porphyry. PLACER DEPOSITS. The mountain masses bordering the South park on the north and west have, owing to the great elevation, been exceptionally exposed to glacial action. An enormous amount of detrital material has in consequence been accumulated in the valleys radiating out from them, which, when rearranged and concentrated, forms valuable placer deposits. The first placer gold was discovered in Tarryall creek in the fall of 1859, and placer mining has been carried on since that time with more or less vigor in the valleys of the Tarryall and of the Platte. 76 PRECIOUS METALS. Near the town of Fairplay the banks of the Platte expose a thickness of over 50 feet of gravel, which has been extensively worked over by sluice raining, but is now abandoned. At present, active work is confined to the valley of the Platte opposite Alma, where hydraulic working is carried on and a gravel bed of over 60 feet in thickness on the east bank of the creek is being developed. Two important conditions for hydraulic mining on a large scale are present in the county : first, an enormous amount of gravel, and second, an abundance of water. It only remains to be practically proved whether these accumulations of gravel are sufficiently rich to pay for working. LAKE COUNTY. Lake county is of small area, having only 450 square miles of surface, and occupying only about 20 miles of the upper valley of the Arkansas, its boundary following the crest of the bordering ranges. Since the discovery of the Leadville mines it- has become second only to Arapahoe county in population, and furnishes three-fourths of the precious- metal product of the state. Its western boundary is the Sawatch range, which is an Archa3an nrnss in which granite predominates over gneiss, and which abounds in dikes of porphyry. The western slopes of Mosquito range on the east, and the hills on the north which form the water-shed between the Arkansas and Grand rivers, have a basis of Archaean granite and gneiss, more or less covered by remnants of the Palaeozoic formations, already described in Park county, which have escaped erosion ; and their lower position relative to corresponding beds on the eastern side of the Mosquito range is due in part to faulting and in part to flexure of the beds. Within these Palaeozoic formations there is an enormous development of eruptive rocks, partly occurring as irregular dikes, but in the main as immense intrusive sheets, following the bedding-planes of the sedimentary rocks. Glacial erosion here, as in other elevated districts, has played an important part in the carving of the present mountain outlines, and in the flood period following the first cold maximum of the Glacial epoch a lake was formed, which occupied the head of the Arkansas valley, and was probably almost entirely included within the present boundaries of the county. The stratified gravel and sand beds which were deposited at the bottom of this lake now form terrace-like ridges bordering the present alluvial bottom of the Arkansas river. Whether the gold contents of these gravel beds, like those of California which may have had a similar origin, will be found to be, in any portion of them, sufficiently concentrated to be worked at a profit is a question which no steps have yet been taken to solve. The gravels resulting from the carving by erosion of the later-formed gulches have, however, been found to contain paying quantities of gold ; and it was to the exceptional richness of those of California gulch, discovered in the spring of 1860, that the development of the enormous silver wealth of the Leadville region is indirectly due. Of late years the prominence given to silver mining has diverted attention from the gravel deposits, and their development has been practically stopped. It is probable, however, that a profitable field for hydraulic mining will be found in this county. The mineral product of the county is mainly confined to tte California mining district or the mines immediately adjoining Leadville, those of the outlying districts furnishing out a small fraction of the aggregate product. The ores are mainly argentiferous galena associated with zincblende, and, exceptionally, a little copper. They are essentially smelting ores, and their value is greatly enhanced by the fact that thus far they have been found in an oxidized condition, the lead occurring as carbonate, the silver as chloride, in a clayey or siliceous mass of hydrated oxides of iron and manganese. Here, even to a greater degree than in Park county, the main body of the ore is confined to the horizon of the Blue or Lower Carboniferous limestone, which is here invariably covered by an intrusive sheet of White or Leadville porphyry. The ore was at first supposed to be confined to the immediate contact of the limestone with the porphyry; but as developments have proceeded it has also been found to extend into the body of limestone sometimes to a depth of over 100 feet from its upper surface, and in such cases in large but very irregular deposits, as is characteristic of ore masses occurring in this rock. Less important ore bodies, generally carrying gold rather than silver, are found at other horizons, either along bedding-planes or in gash veins crossing the stratification. Such are the Colorado Prince and Miner Boy, in the Cambrian or lower quartzite, and the Green Mountain, Tiger, and Ontario, in the Weber grits, or Middle Carboniferous. The first mine opened in the district, and the one which has produced the largest amount of gold, is the Printer Boy, which is a deposit of free gold with carbonate of lead and galena, passing in depth into auriferous copper and iron pyrites, which occurs in a body of quartz-porphyry along a vertical plane or pair of planes nearly parallel, either as cross-joints or fault-planes. The gangue material is simply a white clayey mass resulting from the decomposition of the porphyry itself, and, although at times exceptionally rich, the ore seldom shows any visible metallic minerals. The Palasozoic formations and accompanying intrusive beds of porphyry have been compressed into gentle folds and broken by a series of faults having a general north and south direction whose movement of uplift is as a rule to the east. The prevailing eruptive rock is the White or Leadville porphyry, which generally occurs above the Blue limestone, but is also in places found below it and at other horizons. Besides these there are other intrusive sheets of different varieties of. quartz-porphyry, generally of extremely local development. Along the western end or lower portion of the spurs of the Mosquito range on which the mines are situated the.actual surface of the ground is very largely buried to a depth of 100 feet or more beneath an accumulation of rearranged glacial or moraine material, locally called icash. The extremely complicated conditions resulting from this state of things renders it impracticable within the limits of the present sketch to give any detailed description of the geological structure of the district, and the reader is referred for this purpose to the memoir of the writer on "The Geology and Mining Industry of Leadville". GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 77 The most important groups of mines of the normal Leadville type, taken in the order of their development and of their relative distance from the valley, are as follows : (1.) Those of Fryer hill, which is the western extremity of a spur adjoining Evans gulch on the south, including the Chrysolite, Little Pittsburg, Little Chief, Amie, Climax, Dunkin, Matchless, and Lee mines. In these mines the ore bodies, which reach a maximum thickness of 90 feet, lie in an approximately horizontal position, and are included between two sheets of White porphyry. In some cases these ore bodies are split up by the porphyry into two or more distinct bodies. They are distinguished from the deposits in other portions of the district by the almost entire absence of the original limestone, of which they are a replacement. (2.) The mines of Carbonate hill, which adjoins California gulch on the north, include the Carbonate, Yankee Doodle, Crescent, Catalpa, Evening Star, Morning Star, Henrietta, .JDtna, and Peudery. Of these the seven first-named follow the contact of the limestone and the overlying porphyry on its dip into the hill at an angle of from 15 to 25 degrees, and are east of Carbonate fault, which runs across the face of the hill, while the last two find the limestone at a lower level on the west side of the fault. (3.) To the west of Carbonate hill a second shoulder of the spur is Iron hill, which has been elevated to its relatively higher position by the movement of the Iron fault, which, like that of Carbonate hill, runs along its western base. Here the principal mines are those belonging to the Iron Silver Mining Company, which with the Smuggler, and, south of California gulch, the Eock and Dome, find their ore at or near the surface of the easterly dipping limestone, while the ore of the Silver Wave and Silver Cord, also on Iron hill, and of the La Plata, in California gulch, is mainly found in approximately vertical but extremely irregular bodies extending down into the mass of the limestone. Other^important mines of this type are (4) the Florence group, on Printer Boy hill, north of Iowa gulch ; (5) the Long & Derry group, on the opposite side of the gulch, and on Breece hill (6) the Highland Chief group, overlooking Evans gulch. On Yankee hill are the Andy Johnson, Chieftain, Scooper, and others. While in Stray Horse gulch the Double Decker and adjoining mines have gold ore in the low"er quartzite, the Adelaide and -Argentine find carbonates of lead at the contact of the White pdrphyry and fhe upper portion of the Silurian formation. MINERALS. The most common minerals are cerussite, anglesite, pyromorphite, and galena ; chloride, chloro- bromide and rarely iodide of silver; iron, generally as hydrated sesquioxide, but in the Breece iron mine as red hematite and magnetite, also in the deeper workings in the form of pyrite; manganese generally as a sort of wad, and frequently also as pyrolusite; zinc as calamine or silicate, and in depth as zincblende; bismuth as sulphide and as sulpho-carbonate in the Florence mine; vanadium as dechenite, or vanadate of lead and zinc, in the Morning Star and Evening Star mines. More rarely, native sulphur is found as a decomposition product of galena ; also native gold and silver in the limestone deposits. Arsenic and antimony show themselves in the products of the smelters, the former very persistently, but are seldom found as definite minerals in the ores. Outside the California district, the principal mine is the Homestake, on Homestake peak, in the northwestern corner of the county, which was developed before the discovery of the silver ores of Leadville. It is a rich body of argentiferous galena in Archaean gneiss, and is said to have produced at one time a considerable quantity of nickel ore in the form of an arsenical nickel mineral supposed to be gersdormte. A number of less important mines have been developed along the western slopes of the Sawatch range in the Archa3an which have produced small quantities of pyritiferous ores carrying galena. Their main value lies in the silver which they contain, which is also accompanied by a certain amount of gold. They are mostly reduced in the amalgamating mills which have been erected at Leadville for treating the few siliceous ores of the district which are free from lead. The comparative poverty of the mineral deposits of this district in gold is remarkable when one considers the exceptional richness of many of its placers. In the normal silver deposits of Leadville gold is present, if at all, in very minute quantities; so that it is not detected by the assayer, but is only found concentrated in the bullion. That it exists, however, is proved by its having been found occasionally in the state of native gold in the limestone deposits ; for instance, in those of the Florence mine. GUNNISON COUNTY. Guunison county lies to the west of Lake and Chaffee counties, its eastern boundary being formed by the crest of the Sawatch range. It originally included only the mountainous country connected with this range and the group of the Elk mountains which branch off from it in a northwesterly direction. Since the recent cession of the lands of the Ute Indian reservation it also includes a large portion of this reservation in the Colorado plateau region, extending to the boundary of Utah. Its present area of 11,338 square miles is greater than that of any county in the state. The plateau region, as yet comparatively unexplored, is mainly occupied by nearly horizontal beds of Cretaceous and Tertiary age. Except, therefore, where the underlying Archaean rocks have been exposed by deep erosion, or the later formations have been traversed by masses of eruptive rock, this region affords little promise of return to the prospector in his search after deposits of the precious metals. In the eastern mountainous region, on the other hand, the geological conditions are such as to lead one to expect widespread and important deposits of metallic minerals. Owing to its isolated condition, being separated from the rest of Colorado by high mountain ranges whose lowest passes are over 10,000 feet high, and having been but recently reached by lines of railroad, but 78 PRECIOUS METALS. few actually producing mines have yet been developed within its limits. In spite of the fact that it is penetrated by two lines of railroad, the Denver and Eio Grande and the Denver and South Park, its conditions would be unfavorable for the treatment of low-grade ores the true source of wealth of a mining region on account of the high grades -which have to be overcome by these roads in reaching it, and which, therefore, enhance the cost not only of supplies, but of the movement of ore and fuel, were it not for the fact that it contains within itself the means for treating its own ores at low cost in its coal beds, which are not only exceptionally well situated for mining, but are of a quality probably superior to any on the eastern slope of the mountains. On the completion of the extension of the former road to Utah it will have an additional outlet in that direction, free from the drawback of exceptionally heavy grades. The geology of the western slope of the Eocky mountains presents certain contrasts to that of the eastern. In the latter region, although along certain shore-lines, by unequal erosion, beds of different horizons are found abutting against the underlying Archajan, in general the lowest Cambrian beds are those which rest directly upon it. In the western region, on the other hand, erosion discloses crystalline gneisses and granites, presumably belonging to the Archaean, in direct contact with horizons as high as the Cretaceous, and at points far removed from any well-defined shore-line. The sedimentary beds also dift'er somewhat in lithological constitution, and are, as a, rule, considerably thicker than corresponding beds on the eastern slope. Again, the coal-forming period, which on the eastern slope was at the very close of the Cretaceous (or, as some have maintained, at the commencement of the Tertiary), in the western region, .to judge from the testimony of the thickness of beds overlying it, occurred considerably before the close of this epoch. The ore deposits also, which there are found mainly in the Archaean or Palaeozoic formations, in the Gunnisou region are found to occur also in the Mesozoic formations even as late as the uppermost portion of the Cretaceous. The bituminous coals of the Cretaceous formation, which are generally called lignites, but not it seems with absolute propriety, are here locally transformed into semi -bituminous and even into anthracite coals of excellent quality. The geological structure of the Elk Mountain region is one of such extreme complexity that only the barest and most general outlines can be presented in the limited space here allotted. According to Mr. W. H. Holmes, its structure is that of a great fault-fold, ?. e., an anticlinal fold, running generally with the axes of the range and broken along its crest by a fault, the eastern slope of the anticlinal being relatively gentle, but the western so steep that in one portion the beds are actually inverted. Of the sedimentary beds involved in this fold only the Carboniferous, Trias, and Jura have escaped erosion in the higher portion of the mountains, while the Cretaceous beds are left along its flanks. In the center of this fold Mr. Holmes places a mass of eruptive granite. The writer has had no opportunity of verifying Mr. Holmes' observations in the center of the range, but is quite ready to accept his solution of the structural problems involved, while making a mental reservation as to the existence of eruptive granite at this point. From observations made during a hasty visit to the southern slopes of the range along Slate creek and the heads of Ohio and Anthracite creeks he is inclined to think that this eruptive body may belong, as do the eruptive masses there, to the porphyries of Mesozoic age and of the Mount Lincoln type, already described in the section on Park county. These rocks here break through the Cretaceous strata, not only in narrow and well-defined dikes, but in immense masses, forming entire mountains of most picturesque outline, of which Crested butte and Gothic peak form the simplest type, relics of nearly horizontal Cretaceous strata extending up their sides for several hundred feet above the bottoms of the present valleys. These porphyries in .the region visited are indicated on the Hayden map either as eruptive granites or as Tertiary volcanic rocks. Since they break through the Cretaceous beds, they must have been erupted in post-Cretaceous times, but probably before the deposition of any distinctly Tertiary beds, and their mode of occurrence and lithological characteristics are quite different from those of Tertiary volcanic rocks. The intrusion of such enormous masses of molten material has produced an extensive and widespread metamorphism of the sedimentary beds, and may probably account for the change of the bituminous coals to anthracite. The Elk mountains are evidently of later age than the Sawatch, and, very possibly, even later than the Mosquito or Park range. The ore deposits of the Ruby district must be of post-Cretaceous age, since they traverse Cretaceous rocks ; but as to the age of deposits occurring in the older rocks no data are yet at hand. Ore has been found in almost every portion of the Elk mountains and on the flanks of the Sawatch. The principal mining centers are Aspen, on the northeast slope of the Elk mountains, and Independence, on the west slope of the Sawatch, in the drainage of Eoaring Fork; Euby, Gothic, and a number of small towns on the southwest slope of the Elk mountains ; and Pitkin and Tin Cup, on the southwest slope of the Sawatch. At Independence sulphuret ores carrying silver are found in the Archaean. The Gold Cup mine, near Alpine pass, in the Tin Cup district, occurs in a black, fine-grained limestone, not unlike the Carboniferous limestones of the Mosquito range. Its ore is a silver-bearing cerussite, associated with some oxide of copper in a ferruginous and siliceous gangue. Of the ore deposits occurring in the Cretaceous rocks in Euby district the Forest Queen mine may be taken as a type. The vein material seems to be a decomposed porphyry; probably a narrow dike traversing the Cretaceous sandstones, and standing in an approximately vertical condition. The ore is largely ruby silver and arsenical pyrite, occurring in small crevices and fissures in the decomposed porphyry. The gangue material is sometimes simply an indistinctly banded quartz. GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 79 CHAFFEE COUNTY. Chaft'ee county occupies the valley of the Arkansas river between the crests of its bounding ranges from the southern boundary of Lake county down to Fremont and Saguache counties, a little below the mouth of the South Arkansas. Its mountain slopes are composed of Archaean rocks, mainly granite, traversed by porphyry dikes, with occasional remnants of Palaeozoic formations in the southern parts which have escaped erosion resting on their crests. The valley bottom, as in Lake county, contains stratified beds of gravelly formation and of recent date ; but whether they are of the same age as the Lake beds of Lake county, or have been formed in the Tertiary period, is not yet definitely known. The more recent gravel deposits at the mouth of the larger canons, as well as those along the bed of the Arkansas river, yield gold. The richest are those at Cash creek, which have been worked since the earliest discovery of minerals in this portion of the country. Its mining districts have but few developed mines, hence data with regard to them are extremely meager. In the neighborhood of the town of Granite gold-bearing veins have been worked on the east side of the valley in former years. Near Buena Vista, also on the east side, is the Free Gold district, so called from the Free Gold mine, which is an auriferous quartz vein in a syenite containing abundant titanite. The foot-wall specimen differs from that of the hanging wall, which suggests the possibility that the vein may be on a fault-plane. The Chalk Creek district toward Alpine pass, on the opposite side of the valley, shows' also syenttic country rock which contains a little quartz. The mines from which specimens were obtained are the Black Hawk. Mary Murphy, and Hortense. The vein material of the two former is a felsitic mass which may be a decomposed porphyry. In the ore specimen the only recognized minerals are pyrite and a black mineral which seems to contain manganese. The ore of the Horteuse is a decomposed quartz-porphyry, from which some metallic mineral has been removed by solution. The Monarch district is near the head of one of the branches of the South Arkansas river. The Monarch mine, from which its name is derived, is a limestone deposit, occurring between a dark-gray limestone above and a fine- grained white limestone below. The horizon of these limestones is not known, but it is very possible that they correspond to the Bine and White limestones of Leadville. The ore, like that of Leadville, is mainly cernssite or carbonate of lead. The Columbus mine, in the same district, occurs in granite, its ore consisting of fragments and crystals of quartz, cemented together by some metallic mineral colored red or yellow by oxide of iron. DOUGLAS COUNTY. Douglas county lies south of Arapahoe county, and extends as far as the divide between the Platte and Arkansas rivers and east of Jefferson county, including a portion of the Colorado range lying east of the Platte canon. As is the case further north, this portion of the range is not yet found to contain valuable metallic minerals. The coal rocks, however, underlie the plain country east of the foot-hills, though as one approaches the divide they are more and more deeply buried beneath the Tertiary deposits of which this mesa-like ridge is formed. Their outcrops can be traced from the Platte canon to the southern borders of the county, approaching nearer and nearer to the foot-hills as one proceeds southward. In the neighborhood of Castle Eock are mesa-like ridges, which extend almost continuously to the eastward; but west of the railroad, and between it and the foot-hills, these ridges are broken by erosion into a series of isolated buttes, and are made up of gravel and coarse conglomerate derived from the Archaean formation, belonging to the Monument Creek Tertiary of the Haydeii survey, whose age has not yet been determined. In the neighborhood of Castle Kock, and for some six or eight miles to the southward, the surfaces of these mesas are covered by a light pinkish-colored rhyolitic tufa, which forms au admirable building-stone, and has been very extensively used for this purpose in Denver. The outlines of this volcanic flow have not yet been accurately determined ; it extends but a short distance east and west, and has an average thickness of about 20 feet. EL PASO COUNTY. More than half of the area of El Paso county, which lies to the south of Douglas, is plain country. Its western mountainous area includes the partially isolated mass of Pike's peak, separated from the main Front range by Dte pass and Manitou park, which once constituted a bay or arm of the Palaeozoic sea. The only mineral of industrial importance thus far developed is coal, of which working mines exist to the east of Colorado Springs. Prospectors after the precious metals on Pike's peak have, however, developed au extremely interesting series of minerals, of which those of the cryolite group may possibly prove of economic importance. The following are the species previously recognized : Microcline, as green amazou stone and other colors; albite; biotite, var. siderophyllite ; quartz, clear and smoky; fluorite; coluuibite; gothite: hematite and limouite as pseudornorphs after siderite: artvedsonitf; astrophyllite ; zircon. In addition to the above the following have recently been determined by the members of the Kocky Mountain division of the United States geological survey: Topaz, phenacite, kaoliuite, a peculiar greeir muscovite, cryolite, thomsenolite, gearksutite, and other fluorides not yet definitely determined. 80 PRECIOUS METALS. FREMONT COUNTY. Fremont county, which lies to the east of Chafl'ee and Saguache counties, includes the canon valleys of the Arkansas after it bends to the eastward arid a portion of the plain country beyond Canon City. Its mountains have a base of Archaean, which in the western portion of the county is covered by Palaeozoic formations, and on the north, toward the South park, by Tertiary eruptive rocks, with probably some older porphyries. Along the foot-hills at Canon City occur the upturned Triassic and Cretaceous rocks, which furnish valuable building- stones. A limestone of the Colorado Cretaceous, which is remarkably pure, is used in making lime and as a flux for smelting- works. From less pure limestone above the Triassic hydraulic cement is made. From 'Jurassic and Lower Cretaceous beds in the plains, as well as in the valley of Oil creek, petroleum has been obtained, and several wells, some over 1,000 feet in depth, have been sunk. As yet no considerable concentrations of oil have been developed. South of Cafion City is a synclinal basin in which the Laramie beds have escaped erosion, and where valuable coal mines have been opened by the railroad companies. CUSTER COUNTY. Custer county lies to the south of Fremont, and comprises the Wet Mountain valley, lying between the Wet mountains or Greenhorn range on the east and the north end of the Sangre de Cristo range on the west. The former mountains are a southern continuation en echelon of the Front or Colorado range, and consist of Archaean rocks, mainly granite, with Mesozoic formations resting against its eastern base. This range is relatively low, and its slopes gentle, except where cut through by deep canons. The Sangre de Cristo range, on the other hand, which is a southern continuation, also en echelon, of the Mosquito or Park range, is a lofty imposing chain, whose rugged outlines suggest a very diifereut composition. It has not been examined by the writer, but presumably consists of the same Palaeozoic rocks that are found in the Mosquito range, resting on an Archaean base and traversed by Secondary eruptive roks, of which the so-called Sangre de Cristo granite, outlined on the Hayden map, is very possibly a variety. The Wet Mountain valley at its widest point comprises a distance of over 20 miles from east to , west between the crests of these bounding ridges. The valley bottom lies near the west side of this depression, its Quaternary covering resting either on the Archaean, or on the eruptive rocks which have broken through it. The principal mines have been developed in the neighborhood of the towns of Silver Cliff and Bosita, and an area of 10 miles east and west and 6 miles north and south includes the greater portion of these. In this area the underlying Archaean is broken through and covered by Secondary eruptive rocks, among which diabase is the only type which has as yet been definitely determined. To these eruptions have succeeded flows of andesite and rhyolite, which outcrop at Bosita and Silver Cliff. The town of Rositu is situated near the eastern end of the district, in the midst of a group of steep hills with smooth rounded slopes, which project out into the valley from the Wet Mountain range. The town of Silver Cliff, about six miles west of Eosita, is situated on the open plain near a mesa-like ridge, on whose cliff face, from which the town derives its name, are found the silver deposits of the Eacine Boy mine. The rock of which this cliff is formed is a light pinkish-colored rhyolite, showing the characteristic finely laminated or fluidal structure. In the town itself, and along the eastern edge of the cliff, are outcrops of a dark pitchstone, probably a hyaline variety of the rhyolite. Outcrops of granite are found on the plains between Silver Cliff and in the hills around Eosita, rendering it probable that the rhyolite rests directly on the underlying Archa3an. A number of isolated hills rise out of these plains, the most prominent of which is Bound mountain, on which is situated the Plata Verde mine, and about two miles to the northward are the Blue mountains, in which is situated the Bull-Domingo mine. The bottom of the valley, through which runs Grape creek, lies still to the west of Silver Cliff, and has a considerable extent of arable land. ORE DEPOSITS. The ore deposits of this region are in many cases rather exceptional in character, and have given rise to considerable speculation as to their origin. As yet, however, no systematic or exhaustive study has been made of them on which to found a definite and satisfactory classification. Most prominent and remarkable are the Bassick and the Bull-Domingo, each situated near the northern limits of the eruptive rocks, the former a short distance north of Eosita, the latter 7 miles westward, correspondingly situated with regard to Silver Cliff. The characteristic feature common to these two mines is that the ore is found in large bodjes without any definite boundary, forming a coating on irregularly-rounded fragments of the country rock. A favorite method of accounting for this mode of occurrence has been that the ore cavities are old craters or solfataric openings, in which the fragments of country rock have been tossed about and rounded by attrition and coated by a deposition from metallic A-apors and solutions. While the known facts with regard to these deposits are insufficient to afford a positive theory with regard to their origin, the evidence is decidedly against this somewhat startling hypothesis. The country rock of the Bull-Domingo mine is a hornblendic gneiss, and therefore probably belongs to the Archaean. The ore, which is mainly an argentiferous galena, forms a regular semi-crystalline coating from one- eighth to one-quarter of an inch in thickness around the bowlders and pebbles of country rock, and fills the irregular interstices between them. These pebbles are not in direct contact one with the other, but are separated by the metallic coating belonging to each individual pebble. The galena) is frequently covered by a second botryoidal GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 81 coating, probably of a siliceous nature. The deposit is from 40 to 60 feet wide, and strikes in a northwesterly direction. No fresh specimens of the country rock of the Bassick mine were obtained, and its exact nature is not therefore known. It is said to be the same on both sides of the deposit, and to be an eruptive rock. In this case it is probable that it is a breccia, and the ore is a replacement of the matrix. According to Mr. L. R. Grabill, () the deposit is an irregular opening, nearly eFliptical, in horizontal sections from 20 to 100 feet in width, and standing generally vertical to the depth of present developments, i. e., about 800 feet. The fragments of country rock which fill this opening vary in size from one and a half feet in diameter to the smallest dimensions. They are rarely, if ever, in actual contact with each other, while the metallic shells which surround them are tangent. The size of the fragments, as well as the quantity of ore or metallic mineral present, decreases from the center outward, without any definite limit having yet been determined. In the shell or metallic coating which surrounds these fragments Mr. Grabill distinguishes a series of concentric layers, the innermost and thinnest consisting of a mixture of sulphides of lead, antimony, and zinc, carrying about 60 ounces of silver and from 1 ounce to 3 ounces of gold to the ton. This layer is always present. A second coating, not always found, is lighter in color, and contains more lead, silver, and gold. The third shell is mainly sphalerite or zincbleude, reaching a maximum thickness of 5 centimeters, which carries from 60 to 100 ounces of silver, and from 15 to 50 ounces of gold to the ton, with considerable iron, and some copper. This constitutes the principal pay-ore of the mine. The fourth coating, when present, is formed of chalcopyrite, but is much more irregular than the previous ones, and carries as high as from 50 to 100 ounces of gold and silver. Outside of these a fifth thin coating of pyrite crystals is occasionally found. All the layers have a more or less crystalline structure. The remaining interstices between the pebbles are filled with kaolin. Another singular fact connected with the deposit is the occurrence of small fragments of charcoal in cavities between the bowlders toward the outer edges of the ore body, and most commonly near the water-level. These are sometimes partially mineralized, and at others are perfectly unaltered and retain the woody structure. The greatest depth at which they have been found is 765 feet from, the surface. The other minerals found in the mine are calamine, smithsonite, jamesonite, tetrahedrite, free gold, and tellurides of silver and gold in minute quantities. Another type of deposit in the region fills more or less vertical fissures traversing the eruptive rocks which form the hill country around Kosita. The principal of these is the Humboldt-Pocahontas vein, running northwest and southeast, a short distance north of the town. The exact character of the country rock is not definitely known. This ore carries chalcopyrite and fahlerz, with a little siderite, in a gangue of barite. The Eacine Boy mine, near Silver Cliff, forms a third distinctive type, and seems to be an irregular impregnation of the country rock, the ore in general showing a little black staining of some manganese mineral as its only visible metallic constituent. Thin films of chloride of silver are sometimes distinguishable. This is a free-milling ore ef comparatively low grade, but valuable on account of its great mass. Plata Verde mine has not been worked since its mill was finished, and no data are available in regard to the character of its deposit, which is, however, in rhyolitic rock. The ore is chloride of silver, with some snlphurets, impregnating the country rock. The Terrible mine, in the Archrcan, is about 12 miles northeast of Silver Cliff, and has a foot wall of fine-graiued iron-stained gneiss. The vein strikes N. 20 W., and dips 78 NE. Its ore consists of a massive cerussite, sometimes cementing fragments of wall rock, the gangue material being decomposed country rock. The Gem, a newly-opened mine some 12 miles north of this district, is interesting as having afforded specimens of a rich nickel ore. On Grape creek, in the northern portion of the county, a considerable body of titaniferous magnetite has also been discovered. Both these last-named deposits are probably in the Archsean. Ore deposits have also been developed on the east slope of the Sangre de Cristo range about 7 miles west of Silver Cliff. The Verde mine has a vein striking N. 50 W., and dipping 60 SW., said to be in granite. Its ore is a mixture of pyrite and chalcopyrite, with fahlerz. HUEEFANO COUNTY. Huerfauo county, lying south of Custer and Pueblo, is largely a plain country, and only its eastern end, which includes Huerfano park, a southern continuation of the Wet Mountain valley, extends into the mountain region. The surface of the plain country, as well as the bottom lands of Huerfano park, which was a bay in the original Archrean shore-line, is covered by Cretaceous deposits ; and it is only along the crests of the bounding ridges, the Wet mountain and the Sangre de Cristo, and near the eruptive mass of the Spanish peaks, that the rocks liable to carry metallic minerals are exposed. The schedule reports furnish data from only a single mine, the Mountain Monarch, in the Third Judicial district. This mine is situated on the north slope of the West Spanish peaks, about 10 miles south of La Veta. Its deposit is said to be a fissure vein running east and west, with a shallow dip south, and is from 3 to 6 feet wide. The ore is a banded vein material, consisting of galena, pyrite, chalcopyrite, and fahlerz. The country rock is said to be granite, and the gangue material porphyry. No specimens of either were sent in, but it seems probable to the writer that both belong to the crystalline quartz porphyries, whose mode of occurrence has been already described, and which correspond with what is known of the eruptive mass of the Spanish peaks. a Trans. A. I. M. E., August, 1882. VOL 13 6 82 PRECIOUS METALS. THE SAN JUAN REGION. GEOLOGY. The San Juan mining region, which embraces San Juan county, with the adjoining counties of Hinsdale, Ouray, La Plata, and portions of Rio Grande and Concjos counties, takes its name from the San Juan mountains, a lofty and irregular mass, which, like the Elk mountains, have a general northwest trend, but are of still more irregular structure, and have an even greater predominance of eruptive rocks. Owing to the prevalence of the latter, which constitute the mass of a great portion of the mountain region, the structure of the sedimentary beds is necessarily very indistinct, and the geological data which are obtainable are of the most unsatisfactory nature. The eruptive rocks occur in great masses, sections 2,000 and ;5,0()0 feet thick being shown in the different canons, their most characteristic and striking feature being the occurrence of immense breccia beds over wide areas throughout the region. The entire mass of these rocks has been classed by the members of the Haydeu survey among the Tertiary eruptives, and they have been colored on the map as either trachytes or basalts. While basalts undoubtedly do occur, and trachytes may be found, these or later flows cover bodies of earlier eruptive rocks, and it seems probable to the writer that tdie deposits in the region will be found to occur mainly in the latter. This idea is supported by the examination of the specimens of the country rock brought in by census experts. Although these specimens were mainly in a condition of alteration so far advanced as is common among eruptive rocks in the neighborhood of mines that their original condition could rarely be definitely determined, some undoubted porphyries, diorites, and diabases occur among them, and the others can be referred, with more or less probability, to varieties of one of these types, while among the eighteen specimens which were examined microscopically only a single undoubted Tertiary rock (basalt) was found. This occurs as the foot wall of the Ohio Consolidated mine, in Hinsdale county. In some of the valleys erosion has exposed granite and gneiss, presumably of Archaean age, underlying these eruptives. At the head of the Uncompahgre river, near Ouray, beds of Paheozoic and Lower Mesozoic age are found resting on the granite and sinking to the northwest under the Cretaceous formations. The latter cover the western portions of the counties of Ouray and La Plata, which, like those of Gunnison and Grand counties, belong to the Colorado plateau region. On the southern slopes of the/ San Juan mountains, in San Juan county and the northeastern corner of La Plata county, there is exposed a considerable area of Palaeozoic rocks, which to the southward pass under the Cretaceous formations of the valley of the San Juan. A large portion of these are of undoubted Carboniferous age. but adjoining the valley of the Animas, on the east, is a mountainous region called the Quartzite peaks, composed of rocks whose age is a matter : of considerable uncertainty. Th limestones which adjoin the quartzite have been considered by Dr. Eudlich as Devonian mainly on the evidence of a single well-defined fossil. This fossil is, however, pronounced by Professor R. P. Whittteld to be a Carboniferous and not a Devonian type. The quartzite formations, which are supposed to underlie these, are called on the map Metamorphic- Palseozoic, the rubric of this formation, however, being included in the Archaean; a seeming contradiction of terms of which the writer has found no explanation. It is probable that thePaheozoic formations thicken to the southward, as they are known to do to the westward; and since the Devonian is well developed in Utah and Nevada, and fossils of the Waverly type have recently been found in Lake valley, New Mexico, it is very possible that this formation may be represented in the region, but its existence cannot yet be considered as determined. ORE DEPOSITS. The most striking feature in the mineral development of the San Juan region is the immense quartz veins traversing the eruptive rocks, which stand nearly vertical, their outcrops projecting like walls from the surface, and often traceable to a depth of several thousand feet along the sides of the deep valleys and canons. According to Mr. R. C. Hills, these veins cross both the older eruptive rocks and what he considers as the overlying Tertiary eruptives ; but it is only in rare instances that the latter have been shown to inclose valuable ore bodies,, these being found generally in the older massive or brecciated rocks, whose prevailing color is some shade of green. Veins are also found in the underlying gneiss and granite ; and in the western portion, especially in the neighborhood of Rico, are deposits in limestones of Carboniferous age, frequently along bedding-planes and at the contact with sheets of intrusive igneous rocks. The deposits of the region are mainly argentiferous. In some, however, gold is the chief pay mineral; in others both gold and silver occur. Free-milling gold ores are, as a rule, comparatively rare, the majority of the ores containing a large admixture of base metals, so that they require smelting. The prevailing minerals are argentiferous galena, gray copper, generally argentiferous or freibergite, and, in the upper part of the deposits^ native silver and pyrargyrite or ruby silver. Bismuth-silver minerals are found in several mines in considerable quantities. Gold is apparently derived in most part from pyrite. Barite is not uncommon as a gaugne material, and fluorite also occurs, although more rarely. Compounds of antimony and tellurium are said to occur, and rarely molybdenite and some nickel minerals. The veins are said to have a banded structure, and the quartz is said to be crystalline. It must be noted, however, at the same time, that in many cases one or both walls are not well defined, and a portion at least of the vein material is quite frequently decomposed country rock. Of the age of these deposits, in the uncertainty which exists as regards the true character of the various country rocks, but little can be definitely said. Mr. Hills, who has devoted considerable study to ore deposits, especially those of Ouray county, divides the veins into three systems, which he regards as distinct and probably of different age: First, silver-bearing veins, standing at high angles (80 to 90) and thin (6 inches to 3 feet wide), with, no gouge or GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 83 selvage, carrying essentially base-metal ores. Second, gold-bearing veins, large and strong, dip about 60, gouge or selvage on one or botli walls, intersecting the former, and tberefore of later age. His tbird class differs from the first only in being wider and stronger and in carrying their ore in persistent bands or streaks. Like them, they stand at u high angle, and sometimes carry bismuth and antimony minerals. These veins are essentially gold bearing, as even when carrying base-metal ores they contain little or no silver. According to Mr. T. B. Comstock, in an article on the geology of San Juan county, (a) the age of the veins of the district is probably post- Tertiary, and in their gradually varying strikes, in which there is little evidence of any systematic parallelism, he finds a tendency to radiate out from certain points which he considers centers of trachytic eruption. As, however, in the nomenclature and classification of eruptive rocks, he follows a system adopted by Dr. Endlich, and which is peculiar to that gentleman, the writer is at a loss to know what value to place on his evidence. He recognizes a primary and secondary system of veins, the latter of which cross the former, and makes the following provisory classification: First, those having a northwest trend, which are pre-eminently gray copper (freibergite) lodes ; second, those with an east and west trend, the bismuth series of lodes, carrying occasionally nickel and molybdenum minerals; third, those with a northeast trend, the telluride series, with antimony and sulphides of the precious metals. From the data gathered by census experts, which are necessarily very incomplete, it appears that hi San Juan county the northwest trend predominates; in the Uncompahgre district, comprising the northern portion of San Juan and the adjoining portion of Onray county, the northeast trend predominates; while in Ouray county these two directions are about equally distributed, the east-and-west trend being in either case of subordinate importance. SAN JUAN COUNTY. Sail Juan county has an area of only 560 square miles, and includes the drainage area of the head of the Aniinas river. Its mines are principally found in the lofty peaks which surround the picturesque and elevated basin of Baker's park and its tributary valleys. They occur mainly in the older eruptive rocks, which here apparently rest directly on a base of gneiss and crystalline schists, presumably of Archaean age. From Baker's park southward the Animas flows in deep canons cut through later sedimentary rocks, which on the east consist mainly of the questionable series classed as Mi'tamorphic- Palaeozoic, and on the west of limestones of Carboniferous age. Of the later eruptive rocks which cover those of Secondary age it can only be said that, in view of the facts developed by recent more exact lithological studies, it is unfortunate that the term ' trachyte" should have been so universally applied, inasmuch as late investigations of other districts where this rock was supposed to exist in large masses prove the normal type to be of extremely rare occurrence. The mines reported by census experts belong to three principal districts: the Animas district, about Baker's park and Silverton; Eureka district, in the northeast portion of the county; and the Uucompahgre district, on the mountains between the Uncompahgre and Animas rivers, which apparently takes in also a portion of Ouray county. The region is undoubtedly one of exceptional richness in mineral developments, so that Mr. Comstock's statement that one-sixth of the area of the county is taken up by lode claims seems scarcely an exaggeration. The subjoined table gives a brief summary of the data obtained from producing mines by census experts: Mine. ANIXA8 IlIrtTKKT. Apen Groop Country rock and vein. Ore and gangne. Bowery Cleveland Consolidated.. Diamond (Emblem lode). Empire Hercule* Highland Mary Jennie Parker . Molas... Greenish, indistinct porphyritlc rock. Undeterminable, Vein strike, NW. ; dip, WPSW.; widti, 4 feet. Altered felsite-porphyry. Vein: strike, N. 80 E. ; dip, 80 S. width, 10 feet. IHoritp (diabase '}. Contains fibrous nralitic hornblende, which may have come from angite : chlorite, enidote, and calciteasde composition products. Vein : strike, S. 27 W. ; dip, 75 W. width, 4 feet. Dioritic (?) rock with quartz in small grains. Vein vertical strike, NW. ; width, 4 feet. Quartz-bearing hornblende-diorite. Vein : strike, N. 45 W. dip, 86 SW. ; width, 7 feet. Diorite? (called syenite). Vein: strike. NW. ; dip, 82 SW. width, 10 foet. Biotite-gneiag. A dike of quartz-porphyry c-uts therein at right angles. Vein vertical; strike, N.62\v". ; average width, 10 feet. Diorite? (called syenite), width, 5 feet. Vein: strike: KW. : dip, 80 SW. j North Star (Sultan mountain) . North Star (King Solomon mountain). Hanging wall white indistinctly stratified rock, consisting of quartz and feldspar between a qnartzitc and a gneiss ; foot wall decomposed porphyry. Vein vertical ; strike, NE. ; width, 6 feet. Very much decomposed porphyry. Vein : strike, N. 36 W. ; dip, 65 SW. Greenish felsitic rock (diorite >). Vein: strike, N. 47 E. ; dip, 74 NE. : width, 40 feet. Galena and cernssite, with grav copper, rich in^ilver (frei- bergite). "Carbonate" ore in quartz, with incrustations of ocher, azn- rite, and malachite. Gangue : altered country. Massive freibergite in gangne of calcite and dolomite, with a little galena. Mixture of galena, freibergit*. and chalcopyrite, with barita between quartz layers, forming banded vein material. Freibergite, galena, pyrite, and chalcopyrite in quartz. Xreibergite, pyrite, and some galena carrying silver. . Galena, freibergite, and chalcopyrite carrying silver, with trace of gold. Argentiferous galena, freibergite, and i-halcopyrite. Quart/ gangne. Galena and barite, with stains of copper minerals. Mas-iive argentiferous galena, freibergite, anil zincblende, with a little pyrite. Argentiferous galena and cemssite, with freibergite. a Trans. A. I. M. E., August, 1882. 84 PRECIOUS METALS. Mine. LAS ASIMAB DISTRICT COnt'd. Philadelphia Pride of the West Country rock and vein. EUKEKA DISTRICT. Adelphi Big Giant. Bonanza tunnel , Columbia . Mastodon . Sioux City Tom Moore UNCOMPAHUUE DISTRICT. Alabama No specimen. Called " trachyte ". Vein: strike, NW.; dip, 71 S W. ; 24 feet wide. Dark preen compact decomposed rock, in part breccia. Undeter- minable. Vein: strike, NW.; width, 28 feet Quartz-free plagioclase rock, with crystalline gronndmass, probably diorite. Basic silicate changed to chlorite and calcitfl. Vein : strike, NE. ; dip, 78 SE. ; width, 3 feet. White quartz-porphyry, width, 23 fflfct. Vein : strike, K. 50 E. ; dip, 45 SE. ; Porphyrite, with biotite, and probably hornblende, and a little quartz. Much calcite in lilms. Diorite? Vein: strike, NE. ; dip, 86 SE Decomposed greenish rock (diorite?). Vein: strike, N. 40 E. ; dip, 70 SE. ; width, 200 feet. Greenish decomposed rock (diorite?). Vein: strike,N.; dip, 78 E. ; width, 4 feet. Greenish decomposed rock (diorite). Vein nearly vertical; strike, NE. ; width, 00 feet ; pay streaks, 9 inches to 5 feet. Greenish eruptive roek, with porphyritic crystals and included fragments of red quartzite. Vein : strike, NE. ; dip, 70 E. ; width, 25 feet. Alaska I Diorite or diabase microscopically similar to that of the Adelphi. .Vein: strike, NE.; dip, 80 SE. ; width, 30 inches. Annie Wood. Bonanza. Button. Maid of the Mist. Mammoth . Ked Cload. Hanging wall (?) plagioclase-hornblende rock; diorite (?) ; foot wall (?) much allured porphyritic diabase; groundmass, crys- talline. Vein : strike, N. 20 to 30 E. ; dip, 80 E. ; 5 feet wide. Greenish felsite-porphyry much altered. Vein: strike, N. 65 E.; dip, 80 SE. Light-colored decomposed porph\ ry . Vein : strike, N. 20 E. ; dip, 70 SE. ; width, 4 feet. Plagioclaso rock , with both hornblende and angitc. Porphyrite ordiabase (?). Vein: strike, N. 20 E. ; dip, 65 E. Greenish decomposed porphyry ; basic. Vein : strike, N. 10 E. ; dip, 72 SE. ; width on surface, 30 to 60 feet. Too much altered for determination. Vein: dip, 75 SE. ; width, 3 feet Red Rogers i Greenish country rock ; decomposed porphyry. Vein: strike, N. 5u E.; dip, 80 SE. ; width, 4 feet. Saxon Green decomposed porphyry. Vein: strike.NE.; dip,85 SE.; width, 30 to 40 feet. Ore and ganguo. Freibergite ; a little galena, with silver and some gold, in quartr gangue. Massive argentiferous galena, with chalcopyrite and freibergite. Massive freibergite, with barite and some ohalcopyrite.* Freibergite, argentiferous galena and pyrito, with quartz. Occurs in two parallel veins, ono carrying galena, the other frei- bergite and barite. Freibergite, with some galena and pyrite. Massive argentiferous galena, with layers of qnartz parallel to the cube faces ; zinc blende, pyrite, and oholcopyrite also occur. Mainly galena ; some gray copper. Argentiferous galena and zincbleude ; mussive. Argentiferous galena and fivibergite, with some pyrite and chalcopyrite. Gangne : quartz and feldspar. Chiefly freibergito, with some galena, and containing bismuth-sil- ver iu considerable quantity. Freibergite, stephanite, ruby silver, sulphide of bismuth with chalcopyrite. Freibergite and chalcopyrite with barite. found. Quartz gangue. Galena and pyrite also Gaugue : Argentiferous ealena with cbalcopyriteand zinoblende. quartz and altered country. Argentiferous galena, freibergite and zinoblende, with chalco- pyrite and pyrite. Gangue : quartz and altered country. Freibergite, stepbanite, ruby silver, native silver, sulphide of bis- muth, with pyrite iu quartz and altered country. Argentiferous galena, freibergite, zincblende, chalcopyrite, and pyrite, with some gold in qnartz and altered country. Freihergite, stephanite, ruby silver, with barite and qnartz ; a little galena. Freibergite, galena, and stephanite (?), with some chalcopyrite. Gangne: qnartz. OURAY COUNTY. / Ouray county includes the northern and western slopes of the San Juan mountains, with certain outlying groups belonging geologically to the same mass, and the plateau country extending westward from thence to the Utak line, which is composed mainly of nearly horizontal Mesozoic beds. The development of the precious metals has been thus far confined, as might be expected, to the eastern and more mountainous portion of the county. In the neighborhood of Ouray, which is near the northwest limit of the eruptive area of the San Juan mountains, erosion has exposed the underlying Paleozoic formations and a small area of what is presumably Archreau. The deposits of the northern portion of the Uncompahgre district occur mostly in the sedimentary beds, but in general are more or less closely connected with the overlying eruptive rocks. The veins belong more generally to the metamorphic type, although there seems to be no marked change in their mineral constitution. Mineral Farm seems to be a somewhat exceptionally rich deposit in limestone. In Sneffles district to the west of Ouray, in Upper San Miguel district, and in Iron Springs district near Ophir, to the south, the veins, like those of San Juan county, are in eruptive rocks, and stand at a high angle, many of them, especially in the latter district, carrying considerable gold. In the neighborhood of Rico, still farther south, the ores occur in sedimentary rocks, in general parallel with the stratification and with either foot or hanging wall of porphyry. They are essentially silver-bearing, and have a clay gangue material colored by hydrated oxides of iron and manganese. Mine. UXCOMPAHGRE DISTBICT. Country rock and vein. Uegola ; Blue-gray crystalline limestone, with chert segregations. Quartz- poiphyry is said to occur. I>exter j Hanging wall greenish folnitt>porphyry, and shale below. Foot wall shale, and quartzite below. Vein : strike, N. 20 E. ; dip, 30 E. with country ; width, 18 inches. Golden Gate . Grand View . White quartzite. Vein : strike N. 20 W. ; dip, 80 AV. ; width, 4J feet. Sandstone and conglomerate overlaid by eruptive rock, Vein: strike, N. 82 W. ; dip, 77 S. ; 18 inches wide. Ore and gangue. Argentiferous galena, chalcopyrite, and pyritc, with froiberpti- and stibuitt! (?). Gangue: quartz and barite. Massive argentiferous gulena, native silver, stephanite, zinc- blende. Chalcop\ rite and pyrite are said to occur. Gangue: quartz and altered country. Argentiferous galena, freiborgite, chalcopyrite, and pyrite in quartzite. Pyrito and chaleopyrito, carrying gold and silver, impregnating country rock. GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 85 Mine. UXCOMI'AIIGBK DISTRICT COnt'd Riverside Union 8XEFFLE8 DISTRICT. Potoei Terrible U. S. Depository Virginius Country rook and rein. Green porphvritic rock called trachyte. Vein : strike, N. 50 E. i dip, 78 S. ; width, 4 fret. Gray porphyritic rock called trachyte. Vein: strike, N. 40 W. ; dip, 80 S. : width, 7 feet. Wheel of Fortune Yankee Boy PIOXBRR DISTRICT. Grand View Hope Newman UPPRR 8AM MIGUEL DISTRICT. Alto Cimmarfon .................... Greenish fetaitic rock, locally called trachyte. Vein : strike. NE. : dip, 65 NW. Probably altered diabase. Vein : strike, N. 80 W. ; dip, 85 S . . . Undeterminable brecciated eruptive rock, locally called trachyte Vein: strike, N.37 W. ; dip, 75 SW. ; width, 5J feet. No specimen ; locally called trachyte. Vein: strike, N. 32 W.; dip, 80 SW. ; width, 4 feet Porphyritic rock like that generally called trachyte in the region. Vein : strike, N. 5 W. ; dip, 60 \V. ; width, 5 feet. No specimen ; locally called trachyte. Vein: strike, y. 85 W. ; dip, 85 S. Hanging wall decomposed porphyry or porphyrite; foot wall blue fine grained dolomite. Deposit : dip, 45 to 72 NE., 2 to 14 feet thick. Hanging wall porphyry (?). Foot wall limestone. Vein: dip, 25 NE. ; deposit, 1 to 8 feet thick. Hanging wall dark argillaceous shale. Foot wall porphyry or porphyrite. Vein: dip, 8 NW., 6 feet thick. Undeterminable; called trachyte. Dike of altered porphyry(?). Vein : strike, N. 75 W. ; dip, 70 If. Ore and gangne. Argentiferous galena, with pyrite and a little freibergite. Argentiferous galena, ebalcopyrite, and pyrite, and some ste- phanitc. Freibergitr. strplianitf. and argentiferous galena, in white quartz and decomposed country. Mainly argentiferous galena. Gangne: quartz and altered conn - try. Argentiferous galena, zincblende, and freibergite. with some pyrite. Argentiferous galrna and freibergite. Gangne: quartz aud al- tered country rock. Stephauite and froibergite. Gangue : quartz and porphyry. Argentiferous galena and zincblende, with barite and chalcopy- rite. Gaugne: quartz and altered country. Oxides of manganese, carrying silver, probably as chloride or sulphide. Hydrated iron and manganese oxides, carrying silver. Iron-stained clayey mass, carrying silver, carbonate of lead, and" other minerals. Decomposed rock, probably porphyrite or diabase, strike, N.22 E. ; dip, 75 SE. ; width, 3 feet. Vein : Gold King Undeterminable. Porphyry (?) Vein : strike, N. 22 E. ; dip, 75 SE. ; width, 3 feet. N. W. H.,jr Greenish brecciated undeterminable eruptive rock called trachyte. Vein: strike, N. 10 W. ; dip, 82 W. ; width, 12 feet Palmyra Pandora & Oriental. Smuggler Summit IKON rBraa Uontoznma. Nettie Nevada Osceola Parson Pike Valley View . What Cheer . Locallv called trachyte. Decomposed porphyry. Vein: strike, N. 35 W. , dip, 65 NE. ; width, 4 feet. Greenish undeterminable rock, locally called trachyte. Vein : strike, N. 72 E. ; dip, 60 S. ; width, 10 feet. Greenish undeterminable breccia, locally called trachyte. Vein : strike, N. 18 W. ; dip, 65 W. ; width, 10 feet. Undeterminable eruptive rock locally called trachyte. Vein : strike, NE. ; dip, 75 NW. ; width, 4' feet. Crystalline quartz-porphyry. S. ; width, 4J feet. Vein : strike, E. and W. ; dip, 55 White "siliceous limestone". (Porphyry') Vein: strike, NW. ; dip, 66 NE. ; width, 44 feet. Called trachyte. No specimen. Vein vertical ; strike, NE Biotite-porphyrite. Vein : strike, N. 88 W. ; dip, 70 N. ; width, 4 feet. Fine-grained very crystalline quartz-porphyry. Vein : strike, E. aud W. ; dip, 60 N. ; width, 5 feet Syenite or diorite (?) with a little quartz. Vein: strike, N. 15 'E. ; dip, 75 W. ; width, 4 feet. Called trachyte. No specimen. Vein, vertical ; strike, NE. ; dip, 90 ; width', 3 feet Quartz-porphyry. like Lincoln porphyry. Vein, vertical; strike, N.40E.; width, 4 feet. Argentiferous galena and freibergite, with barite and quartz. Several parallel veins. Argentiferous galcnn, freibergite, chalcopyrite and pyrite, with some free gold. Gangue: light-colored felsitic rock, banded parallel with walls. Gold-bearing quartz in altered country rock. 1 Quartz impregnated with ?alena, zincblende, chaleopyrite, and pyrito, carrying gold and silver. Gangue : quartz and altered country rock. Argentiferous galena, with barite and stibnite. Gangue : quartz and altered country. i Auriferous quartz, with pyrite and chalcopyrite. Native silver, stephanite, argentiferous galena, and zincblende. Gangue : quartz and altered country. Argentiferous galena, cernssite, with stephanite and freibergite. Gangue : quartz and altered country. Galena, ccrussite, with some chalcopyrite, in quartz and altered country rock. Galena, pyrite, and auriferous iron-stained quartz. Galena, freibergite, chalcopyrite. and pyrite. Gangue: qn.irti and porphyry. Iron-stained auriferous quartz. Gangne: quartz and altered country. Argentiferous galena, zincblende, pyrite, and barite. Gangne: quartz and altered country. Argentiferous galena and pyrite, with a little gold, in gangue of dolomite and quartz. Argentiferous galena and cernssite. Argentiferous galena and freibergite, with chalcopyrite, pyrite, and zincbleude. Gangue : quartz and altered country. LA PLATA COUNTY. La Plata county lies to the south of Ouray and San Juan counties, and is largely a mesa country formed of approximately horizontal Mesozoic beds, protruding through which are the eruptive masses of the La Plata mountains and the Sierra el Late. The coal horizons underlie a large portion of the county, as well as a portion of western Ouray, and developments have been made in the more thickly settled portions. In the census year its mines were mostly in the condition of prospects. A schedule was obtained from only one producing mine, the Comstock, in the California district, on the west side of the La Plata river, and 2 miles north of Parrott City. Its ore deposit occurs in a dike of felsite-porphyry included in a reddish sandstone or quartzite, lithologically resembling those of the Upper Carboniferous of Park county. The deposit strikes north and south with the formation, dipping 65 to the eastward, and is apparently an impregnation or alteration of the country rock for about 6 feet in width near the hanging wall of the dike. Its ore is auriferous pyrite in a quartz gangue, with scattered spots of galena and gray copper. Specimens have been brought in from an extremely interesting deposit of copper glance in a coarse conglomerate resembling lithologically those which occur in the lower portion of the Triassic formation found to the west of Dnrango. A similar deposit is said to occur in the valley of the Rio Dolores, in the immediate neighborhood of a mass of eruptive rock which traverses the sedimentary conglomerate. 86 PRECIOUS METALS. HINSDALE COUNTY. Hinsdale county lies to the east of Ouray and San Juan counties, its area being mainly covered by eruptive rocks, with some exposures of underlying Archaean in the valleys tributary to the Lake fork of Gunnison river. Its mines occur mostly between Lake City and the crest of the range which divides this county from San Juan. In manner of occurrence of country rock and minerals they resemble those of the latter. Exceptionally, the country rock of the Ohio Consolidated mine, on Henson creek, 15 miles west of Lake City, is a fresh feldspar-basalt, Containing olivine, which is largely altered to serpentine. Mine. Country rock and vein. On' mid gaujrue. OAI.ENA DIBTI1ICT. Cnlifoinift Porphyrite (!) Hnnfrinj> will resemblea decomposed feleite-por- .A rjfcnt herons g:ilenu. IVeibi:rgite. zincbleude. ciialcopyrite, with phyry. Vein: strike N. 57 E.: dip, 55 N w. ; bonded at rue- ' oalclte and rhodocbrocite ('Tin quartz gangne, lure, 4 feet wide. Oc-an Wave Cray cniptive. called traehyte. Vein: strike UK. : dip. 80S. ; Aracntiferoua galena and ireiucrgite: little native copper. width. 4 l'(>et. (Jan;:"!-: quartz and altered country. Ohio Consolidated | Foot wall fresh feldspar-basalt, with olivine alleled to seipeu- , Freiber;iit<- and clml< opvrite. Ganjiuo: quartz and altered roitn- tine; hanging wall nuieh altered basic rock, possibly the try. same. Vein : strike N.r. W. ; dip, 73 W. ; 3J feet wide,' Palmetto - Gray diabuse-porphyrite, with tendency to amygdaloidal struc- ("haleopyrite, atephanite, and ruby silver, with some gold in ture. Vein: itrtke 2T. 25 E. ; dip, 7;j S. ; 4t'e