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.