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]