The above are all the localities of fossils, in Nevada, known to have been published up to this time, excepting those which have been described or noticed in the publications of the Geological Survey of California. Messrs. Meek and Engelmann state, at the end of their paper, that igneous rocks predominate west of the 116th degree of longitude as far as the Sierra Nevada, and that only a few traces of stratified rock were found in that district in none of which any organic remains were observed. The exploration of this region, supposed to be destitute of fossiliferous rocks, has proved, however, that it contains immense ranges of stratified beds which, in a considerable number of localities at least, are highly prolific in well preserved fossils.
As soon as the Humboldt mining region began to be resorted to by miners, which was in 1861 and 1862, fossils were discovered by several persons, who about the same time furnished us with collections of value and interest. The most important of these collections were those of Mr. Gorham Blake and of Mr. R. Homfray. The specimens obtained by these gentlemen, as well as others of the same age obtained by the Survey, near Dayton, Nevada, and also in Genesee Valley, California, were figured and described by Mr. Gabb in the first volume of the Palæontology of California, forming a part of the series of publications of the Geological Survey. The geological age of the formation is that of the Hallstadt Limestone of the Austrian Alps, or the Upper Trias, there being several species at the above cited localities which are identical with European species from this geological position, as determined by Mr. Gabb, and confirmed by Von Hauer, the eminent palæontologist of the Austrian Geological Survey.[27]
Since the publication of the Palæontology of California, Vol. I, our stock of information with regard to the range and extent of the Upper Trias, in Nevada, has been considerably increased by the explorations of members of the Survey, and other persons who have furnished us with specimens from their collections, or given us information as to the character of the rocks noticed by them on their lines of travel. We now know that the Triassic rocks occupy a broad belt of country extending from the 117th meridian west to the line dividing the States of Nevada and California, and lying between the parallels of 38° and 40°. Within the area thus designated, Triassic fossils have been found at several localities, some of which are remarkable for the number and good state of preservation of the various species. Among these localities that of the Volcano District is remarkable for the size and beauty of the Ammonites found there. This is about thirty miles east of the south end of Walker’s Lake. New Pass District, twenty miles west of Austin, is also a rich locality of Triassic fossils At two or three points within this Triassic area there are indications of the existence of fossiliferous rocks occupying a higher position than the Trias, and perhaps of Liassic Age; but the collections have not yet been sufficiently studied to justify a positive opinion on this point.
The sedimentary strata in this region are much broken up and metamorphosed by intrusive rocks, of which there is a great variety, granite being one of the most abundant. In the southern portion of the area designated above as including stratified rocks of Triassic age, a very large part of the surface is occupied by volcanic materials, apparently a continuation of the very recent volcanic masses near Mono Lake. Lava is said to be the predominating rock over the region to the southeast of Walker’s Lake, and as far in that direction as the State line between Nevada and Arizona. The same is true of the region to the north and northwest of Humboldt River, where granitic and volcanic rocks are reported as occurring, and where, so far as known, no fossils have yet been obtained. This, however, is a region as yet but little explored, on account of the number and warlike disposition of the Indians.
Between the 116th and 117th meridians is a region of granitic and volcanic rocks, including two principal north and south ranges, and many spurs and side ranges. The Toiyabe range, in which are the mines of Austin, or the Reese River mines, and which is a little east of the 117th meridian, is mostly granitic. Stratified but highly metamorphosed rocks are said by Mr. Blatchley to occur on its east flank, a few miles south of Austin; these rocks contain fossils, which, however, are nearly obliterated by metamorphism. A box of these, forwarded some time since, has never been received, so that no positive statement can be made as to the age of the formation. From Mr. Blatchley’s description of the forms observed by him, it would appear that we may have here rocks older than the Carboniferous.
East of the 116th meridian, our collections indicate the existence of a broad area covered chiefly by rocks of Carboniferous age, which seem to occupy most of the space between the 115th and 116th meridians. The most western locality of Carboniferous fossils known to us is that on the west side of Diamond Valley, about 70 miles east of Austin, and in lon. 116°. Here, in a dark, crystalline limestone, a variety of species have been obtained by Mr. Clayton, all in a poor state of preservation, but of which the Carboniferous age may be without difficulty made out. Among the genera represented at this locality are Productus—two species, one of which is P. semireticulatus—Spirifer, and Fusulina, probably F. gracilis, besides some indistinctly marked corals. The indications are that these beds are of Lower Carboniferous age. On the east side of Diamond Valley some imperfectly preserved corals have been found, probably Devonian, or possibly belonging to a still older group. The collections from the region included between the 115th and 116th meridians indicate the association of rocks of both Devonian and Carboniferous age in the outcrops. Here our collections do not enable us to do anything more than to corroborate the previously published statements of Messrs. Meek and Engelmann in regard to the age of the formations.
From the Silver Peak District, near lon. 117° 20´, and lat. 38°, an interesting collection of fossils has been brought by Mr. Clayton. The specimens are unfortunately in a very imperfect and fragmentary condition, but they contain the first trilobites which have been brought to our office from any of the Pacific States or Territories. The rock in which they occur is a dark yellowish brown limestone, with intercalated layers of light grey argillaceous shales. Some of them appear to belong to the genus Dalmania, and, if so, the formation is probably of Upper Silurian age, although possibly Devonian. The careful examination of the corals which have been obtained in this district by Mr. Clayton, and also by Mr. Blatchley, will probably throw some additional light on the geological position of these rocks.
[26] On Professor Hall’s Map “illustrating the general geological features of the country west of the Mississippi River,” which accompanied Emory’s Mexican Boundary Report, and was published in 1857, all of a broad central strip running along the parallel of 40° through the center of Nevada, is colored as “lava and other igneous rocks,” while the western portion of the State has several broad belts of “Upper Carboniferous Limestone,” running north and south across it from Walker’s Lake to Goose Lake. So far as I know, no Carboniferous fossils have yet been found in that part of Nevada.
[27] See Jahrbuch der K. K. Geologischen Reichsanstalt, 1865, page 233 of the Proceedings.