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widely as do those of the different zones enumerated by Mr. King. am, in fact, strongly inclined to consider freedom from base metals, for instance, a peculiarity due in many cases to secondary processes, and not to be relied upon as characteristic for single veins even, to say nothing of whole groups, districts, and continental zones.
Nevertheless, the generalizations of Professor Blake and Mr. King on this subject are highly interesting and valuable. The criticism here made is not in opposition to their views so much as in qualification of a possible rash application on the part of the general public. The zonal parallelism does exist, though in a somewhat irregular way; and it is clearly referable, as these writers have shown, to the structural features of the country, the leading feature of which is the longitudinal trend of the mountain ranges.
Subordinate to this trend (or, more strictly, resulting from the same causes as produced it) appear the predominant longitudinal strike of the great outcrops of sedimentary rocks, the longitudinal axes of granite outbursts, and, finally, the longitudinal vents of lava overflows and the arrangement of volcanoes in similar lines. It is evident that in crossing the country from east to west we traverse a series of different formations, while, by following routes parallel with the main mountain ranges, we travel upon the continuous outcrops of the same general age.
Mr. King distinguishes in the history of the entire Cordillera two periods of disturbance which have been accompanied by the rending of mountain chains and the ejection of igneous rocks. Such periods would afford the conditions of solfataric action, thermal springs, and the generation of acid gases and metallic sublimates and solutions, and thus favor the formation of metalliferous deposits. The first of these periods, he says, culminated in the Jurassic, produced over the entire system a profound disturbance, and is, in all probability, the dating point of a large class of lodes. To the second, or tertiary period, he assigns the mineral veins which traverse the early volcanic rocks.
The expression "culminated in the Jurassic," merely refers, no doubt, to the fact that the cretaceous strata of California repose unconformably upon the upturned and metamorphosed Jurassic slates, having been themselves neither tilted nor highly metamorphosed. Perhaps it is well to remember, however, that the cretaceous is a weak point in the California series, at least, as determined by leading fossils; and perhaps the results of more complete stratigraphical surveys will indicate that there are gaps of no little significance, dynamically and chronologically, in this part of the geological record. At all events, the period of the folding of the Sierra Nevada (presumably that of the formation of many metalliferous deposits) was in some sense post-Jurassic, rather than Jurassic; and probably this is the meaning of Mr. King, who speaks of it in another passage as "late Jurassic."
The lodes which are referred to this period are of two types: first, those wholly inclosed in the granites, the outburst of which accompanied the upheaval of the earlier stratified group, or in the metamorphosed Jurassic and sub-Jurassic strata; secondly, those which occupy planes of stratification or jointure, thus following in general the dip and strike of the country rock, while they present in other respects the indications of fissure veins. The veins of the Reese River granite are examples of the first type; many gold veins of California, the Humboldt mines, etc., are given as illustrations of the second. The White Pine district, the mineral deposits of which are said to be inclosed conformably between strata of Devonian limestone, is declared to be "a prominent example of the groups comprised wholly within the ancient rocks."
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 résources 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 bypothesis 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 debris. 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 undoubtedly 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 Victoria, had on one occasion prepared for photographic uses a solution of chloride of gold,