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We have hitherto supposed the strata immediately overlying the argentiferous limestone at White Pine to be deep-water Carboniferous; but their Devonian character seems to be demonstrated in the geological chapter on that subject by Mr. Arnold Hague, quoted elsewhere in this volume. More practically important is the assignment of these deposits to the earlier period of geological disturbance. Mr. King appears here to include in one group all the White Pine deposits, the "Base Range" as well as "Treasury Hill;" yet the striking distinction in mineralogical character is worthy of regard. The deposits of Treasure Hill are notably free from base metals; and it seems to me that in their present form they must be due to a secondary action, which has concentrated and recombined the metallic elements of older deposits. It should be added, however, that although the chlorides of Treasure Hill are as pure as those of Lander Hill, they do not appear, like the latter, to yield in depth to such silver ores as characterize the fissure-veins of Reese River district-ruby silver, for instance. Nor are they fissure-veins, so far as we can now decide.
To the Tertiary period of orographical disturbance are referred the volcanic overflows and the veins wholly or partly inclosed in volcanic rocks. Uuder this head Mr. King classes many important veins of Mexico, several of those which border the Colorado River, in the United States, and, in general, that zone which lies along the eastern base of the Sierra Nevada. The Comstock lode is adduced as the most prominent example of this type, and the Owyhee district in Idaho is also referred to it, because, although in granite, it presents a series of volcanic dikes which appear to prove, by the manner of their intersections with the quartz lodes, that the latter are of Tertiary origin. It will be seen that although the extent and number of the deposits of this class are inferior to those of the earlier period, they include some of the most brilliant instances in the history of mining. As Mr. King, however, points out, many of the veins which are wholly inclosed in the older rocks may nevertheless be due to this later period of disturbance. Nor does he ignore the bearing of this thought on his determination of the earlier period as Jurassic. He confesses that in more recent strata, formed from debris of Jurassic rocks, ore-bearing pebbles have not been found; but he regards this fact as a piece of negative evidence merely. The distribution of mineral deposits east of the Rocky Mountains follows somewhat different laws. Here we have but one longitudinal range that of the Alleghanies, which is accompanied by a gold-bearing zone of irregular extent and value. In the Southern States the strata flanking this range present a remarkable variety of mineral deposits. On the eastern slope of the Rocky Mountains, again, occurs what may perhaps be denominated a zone or longitudinal series of coal-fields. But between these mountain boundaries the geological formations of the country cluster, as it were, around centers or basins. We have such a group in Michigan, another in the Middle States, and a third in the Southwest.
The deposits of the different metals, ores, and useful minerals, in the country east of the Rocky Mountains, vary widely in age. The ores of gold, copper, and iron, in the pre-Silurian schists of the South; the galena and cobalt ores of the Southwest, and the copper ores of Lake Superior, in the lower Silurian rocks; the argillaceous iron ores of New York, and other States west of New York, in the Upper Silurian, and the salines of the same group; the bitumen, salt, coal and iron ores of the Sub-carboniferous; the coal and iron of the Carboniferous; the coal, copper, and barytes of the Triassic; the lignites of the Cre
taceous, and the fossil phosphates of the Tertiary period, are instances which may serve to show how great is this variety. It is not within the province of this report to discuss the mineral deposits of the Mississippi Basin, the Appalachian Chain, or the Atlantic Coast. I shall content myself with brief mention of two points. The first is the greater relative age of the metalliferous deposits as compared with those of the inland basin and the Pacific slope. On this side the period of greatest activity in such formations was over before it began in the West. The great gold and silver deposits beyond the Rocky Mountains appear to be post-Devonian, post-Jurassic, and even Tertiary in their origin. The vast volcanic activity which affected so wide an area in California, Oregon, Washington, Idaho, and Nevada, is not represented in the East.
The other point is the peculiar relative position of our coal and iron deposits. This was eloquently described by Mr. Abram Hewitt, United States Commissioner to the Paris Exposition, in his admirable review of the iron and steel industry of the world. I cannot do better than quote his forcible words:
The position of the Coal-Measures of the United States suggests the idea of a gigantic bowl filled with treasure, the outer rim of which skirts along the Atlantic to the Gulf of Mexico, and thence, returning by the plains which lie at the eastern base of the Rocky Mountains, passes by the great lakes to the place of beginning, on the borders of Pennsylvania and New York. The rim of the basin is filled with exhaustless stores of iron ore of every variety, and of the best quality. In seeking the natural channels of water communication, whether on the north, east, south, or west, the coal must cut this metalliferous rim; and, in its turn, the iron ore may be carried back to the coal, to be used in conjunction with the carboniferous ores, which are quite as abundant in the United States as they are in England, but hitherto have been left unwrought, in consequence of the cheaper rate of procuring the richer ores from the rim of the basin. Along the Atlantic slope, in the highland range, from the borders of the Hudson River to the State of Georgia, a distance of one thousand miles, is found the great magnetic range, traversing seven entire States in its length and course. Parallel with this, in the great limestone valley which lies along the margin of the coal-field, are the brown hematites, in such quantities at some points, especially in Virginia, Tennessee, and Alabama, as to fairly stagger the imagination. And, finally, in the coal basin is a stratum of red fossiliferous ore, beginning in a comparatively thin seam in the State of New York, and terminating in the State of Alabama in a bed 15 feet in thickness, over which the horseman may ride for more than one hundred miles. Beneath this bed, but still above water-level, are to be found the coal-seams, exposed upon mountain sides, whose flanks are covered with magnificent timber, available either for mining purposes or the manufacture of charcoal iron. Passing westward, in Arkansas and Missouri, is reached that wonderful range of red oxide of iron, which, in mountains rising hundreds of feet above the surface, or in beds beneath the soil, culminates at Lake Superior in deposits of ore which excite the wonder of all beholders; and returning thence to the Atlantic slope, in the Adirondacks of New York, is a vast, undeveloped region, watered by rivers whose beds are of iron, and traversed by mountains whose foundations are laid upon the same material. In and among the coal-beds themselves are found scattered deposits of hematite and fossiliferous ores, which, by their proximity to the coal, have inaugurated the iron industry of our day. Upon these vast treasures the world may draw for its supply for centuries to come; and with these the inquirer may rest contented, without further question-for all the coal of the rest of the world might be deposited within this iron rim, and its square miles would not occupy one-quarter of the coal area of the United States.
This vivid description rests upon a geographical rather than a geological grouping. But it is none the less intimately connected with the underlying geological facts. Its strongest application is, however, economical. If any material thing may stand as the type of force, it is coal, the deposits of which may well be called vast storehouses of powerthe product of solar activity through uncounted years-laid up for the use of man; and iron, on the other hand, may symbolize the inert, dead matter, awaiting the touch of power to wake it into efficient life. These are prime elements in our universe of industry. Take them away and our
present civilization is annihilated. Put them together in the hand of an intelligent and mighty nation, and that nation could recall the world from the chaos of barbarism. But they need each other, and it is in the wonderful combination of both, as well as the exhaustless abundance of each, that America finds sure promise of enduring power.
Thus East and West bear witness of our great inheritance of natural wealth. Every period of geological change has been laid under contribution to endow with rich legacies some portion of our land. Our territory epitomizes the processes of all time, and their useful results to man. Divided, yet in a stronger sense united, by mountain chains and mighty rivers, our diversified mineral resources may figuratively represent, as I firmly believe they will literally help to secure and maintain our characteristic national life, a vast community of communities, incapable alike of dissolution and of centralization; one, by mutual needs and affections, as the continent is one; many, by multiform industries and forms of life, as the members of the continent are many.
THE ORIGIN OF GOLD NUGGETS AND GOLD DUST.
The following article, from the pen of Mr. Andrew Murray, F. L. S., which appeared in 1870 in the London Scientific Opinion, corroborates forcibly the suggestions and opinions advanced in my last report (chapter lxi, page 449) upon the same subject. It is to be hoped that a hypothesis so highly probable as that of the solution, precipitation, and aggregation of gold in placers may be subjected to the test of careful experiments and comparisons:
The origin of gold nuggets and gold dust is not so simple or clear as at first sight it appears to be. The natural explanation of the production of gold dust is, that it is the golden portion of the débris of rocks, which have originally had gold disseminated through them. As the wear and tear of ages has crumbled into dust mountains so composed, part of the dust becomes sand, or quartz, or whatever else the basis of the rock may be, and the other part is the liberated gold, from which the quartz has been rubbed away; and if we accept this as the explanation of the production of gold dust, the same hypothesis should explain that of gold nuggets, which are found associated with it. But there are various circumstances which it is difficult to reconcile with this theory. One of these is the occurrence in the drift of nuggets of a larger size and less intermixed with foreign substances than have yet been discovered in any quartz reef; as most people are aware, the gold in reefs is usually disseminated in particles and strings through the quartz-veins or rock, instead of lying in pockets or masses. Another still more remarkable fact, applicable both to gold dust and gold nuggets, is that alluvial gold is generally of a higher standard than that obtained from the reefs. It is needless to say that if it is merely the gold washed or crumbled out of these reefs, it ought to be of identically the same standard and quality. Another objection to the dust being merely the degraded particles released from the rock, is the size of the particles-not nuggets, but particles of dust. Gold being so much softer than quartz, its particles, after being subjected to the same degree of attrition, ought to be vastly smaller. Although of greater toughness than quartz, and possessed of ductility and tenacity, which quartz wholly wants, it is very soft, and, under the influence of the attrition from running water and its accompaniments, ought to be pounded and torn into the minutest fragments; but this is not so. There is, moreover, a marked difference in the appearance of the gold dust from different drifts in different countries. In some it is like dust or sand, in others it is like scales. If subjected to the same influences in all, there seems no reason why the same shape should not obtain in all cases. These peculiarities would suggest that some other influence than mere degradation of gold-charged rocks has been the agent in producing gold dust; but in any and every view, we think it cannot be disputed that degradation must have had some share in the work. It is plain that if a gold-charged rock is reduced to gravel, sand, or powder, particles of gold, of some size or other, or gold in some shape or other, must form part of the débris. These gold remnants should be found in greater quantity, and in greater size, the nearer they lie to the source from which they were drawn, and this we believe also to be the case. The general similarity between gold-producing districts, by which a Californian miner could detect a likely spot for gold in Australia or Kildonan, probably depends rather on the character of the mountains out of which the gold has come than on the mode of production of the manufactured dust, if we may call it so. We imagine that the truth will be found to be that the result is referable to two causes, only one of which may in some cases have been present, in others, both. The first, the ordinary process of degradation and grinding the rocks to fragments; the other, as suggested by Mr. Selwyn, the government geologist of Victoria, that gold has also been taken up in solution by the water permeating the gold-bearing rocks, and that in passing through the drift, in which minute particles of gold lay, it has, from some cause, become decomposed, and the gold held in solution been precipitated and deposited around the most congenial nuclei presented to it, which would nudoubtedly generally be the particles or pieces of reef-gold, or any other metallic substances for which it had an affinity.
We find an interesting paper on this subject in the Transactions of the Royal Society of Victoria, 1867, by Mr. C. Wilkinson, in which he mentions some facts bearing on the subject. It appears that Mr. Daintree, formerly of the geological survey of Victo ria, had on one occasion prepared for photographic uses a solution of chloride of gold,
leaving in it a small piece of metallic gold undissolved. Accidentally, some extraneous substance, supposed to be a piece of cork, had fallen into the solution, decomposing it, and causing the gold to precipitate, which made a deposit in the metallic state, as in the electro-plating process, around the small piece of undissolved gold, increasing it in size to two or three times its original dimensions. Considering this accidental experiment of Mr. Daintree's as in some measure supporting Mr. Selwyn's theory, Mr. Wilkinson followed it up by a few simple experiments in the same direction, which he details in his paper. In his experiments a small chip of wood was generally used as the decomposing agent. In one instance he used a piece of leather. All through the wood and leather gold was disseminated in fine particles, and, when cut through, the characteristic metallic luster was highly reflected. From various experiments it would appear that organic matter is the necessary chemical agent for decomposing a solution of the chloride of gold in order to precipitate the gold as a coherent coating around a nucleus; and that, so far as Mr. Wilkinson had yet tried, iron, copper, and arsenical pyrites, galena, antimony, molybdenite, blende, wolfram, and metallic gold constitute essentially favorable nuclei to determine this chemical reaction. It is to be observed, too, that organic substances, such as fragments of wood, roots of trees, etc., occur abundantly in the gold drifts of Australia. If water holding gold in solution circulates through the rocks and drifts, all the conditions necessary for the production of gold dust and nuggets by deposit are present. Does the water so circulating now hold gold in solution?
One would think it would not be difficult for a chemist in Australia or California to determine the fact by direct experiment, but it does not appear that it has ever been tried. Mr. C. Wilkinson, however, quotes facts which lend probability to the view that when the trial is made the question will be solved in the affirmative. In testing a solid mass of iron pyrites Mr. Daintree found gold throughout. The mass retained the structure of a tree stem, in which the organic structure was replaced by pyrites. It had been taken from the Ballarat drift, and the same experiment was repeated by Mr. Newbury, the geological survey analyst, on another stem taken from the same drift, with a like result. Gold in such deposits assumes a mammillary form, which appears analogous to that presented by the surface of nuggets-a point of some importance, for, in the first place, it is a question whether a mammillary surface is the kind of surface that would be produced by abrasion and attrition; and, in the next place, abrasion or attrition can certainly have nothing to do with its appearance in these golden petrifactions. We cannot avoid attaching the greatest importance in relation to the question to the presence of gold in pyrites that has been formed in wood imbedded in auriferous drifts. The gold must have been in solution when so deposited, and everything will then depend on the age of the so petrified wood. If contemporaneous with the drift, the question is answered. Another fact to the same effect is, that sometimes gold incloses a nucleus of brown iron, etc. This is obviously quite inconsistent with such pieces of gold having been abraded, as they are out of crumbling rocks; such nucleated pieces of gold are never found in reefs. It is the old puzzle of a reel in a bottle. In relation to this we may remark that we believe that nuggets have never been found in the gold-fields of Brazil. We have the authority of Mr. Harding, a gentleman well known for his great practical knowledge of gold mines and mining in that country, that he never met with nor heard of a nugget, properly so called, in all his many years' experience in the gold district of Brazil; but, on the other hand, it is there almost invariably found in veins in connection with or in the vicinity of some other metal, generally iron. In what is probably the most prolific mine of gold that has ever been known in the whole world, that of San Juan del Rey, (the value of which was not long since so seriously depreciated by the accidental destruction by fire of the wooden ladders, supports, and machinery,) the gold is found in a matrix of porous iron or agglutinated iron sand, called Jacotinga, which consists of a bed or vein not a foot in width, but so incredibly rich that on one occasion, when our informant was on a visit to the manager, there was brought in on an assiette, as a sort of dessert for the eyes after dinner, a lump of gold ore that had been extracted that day from the mine. It was about the size of a large fowl; not so big as a turkey, but bigger than a duck. It was a mass of Jacotinga iron, with gold all mingled and streaked through it. The gold, when afterward extracted, was found to amount to 30 pounds weight. On the previous day the amount of gold obtained from the Jacotinga had been 67 pounds, and on the day following 130 pounds, equal in value to about £8,000. We only mention it as a corroborative instance of the concurrent presence of gold and iron. Lastly, as pointed out by Mr. Wilkinson, it must be admitted that the fact that gold may be greatly purified by dissolving and reprecipitating it, is very suggestive of the generally higher standard of alluvial over reef gold being due to a similar cause