462 SCIENTIFIC RECORD FOR 1883. 



characteristic of the Trenton. It is worthy of note that in this group 

 but a single undetermined graptolite is as yet known. At the top of the 

 Eureka quartzite is a marked stratigraphical break, above which occurs 

 the Lone Mountain limestone 1,800 feet thick, containing Trenton fossils 

 in its lower part, and corals, apparently of Niagara age, toward the top. 

 Although this mass is assumed as the summit of the Silurian, it is said to 

 graduate imperceptibly upward into the great Nevada limestone, which, 

 with its interbedded shales and quartzites, has a thickness of 6,000 feet 

 and is characterized throughout by a Devonian fauna, includiug rep- 

 resentatives of Upper Helderberg, Hamilton, and Chemung. The 2,000 

 feet of the White Pine shales, above the Nevada limestone, containing 

 some remains of land-plants, include an invertebrate fauna indicating a 

 passage to the Carboniferous. This has as its lowest member the Dia- 

 mond Peak quartzite, shaly at the base, but for the most part hard and 

 vitreous, again becoming slaty near the summit, and including, about 

 500 feet from the base, a thin band of fossiliferous limestone. Above this 

 comes the Lower Carboniferous limestone (3,800 feet), separated by the 

 Weber conglomerate (2,000 feet) from the Upper Carboniferous, the sum- 

 mit of the Paleozoic column. Both of these limestones are highly fossilifer- 

 ous. The Silurian and Devonian strata of the Lone Mountain and Ne- 

 vada limestones are seen in places in the district to rest unconformably 

 upon the Eureka quartzite, while elsewhere these Carboniferous lime- 

 stones repose directly upon the Pogonip limestones, the whole interme- 

 diate series of 10,000 feet being absent. 



The ancient crystalline rocks of this district are very few. A single 

 small outcrop of granitic rock appears, and porphyroid granites and 

 quartziferous porphyries are described as breaking through and locally 

 altering the Pogonip limestone. The later eruptive rocks, Tertiary and 

 post-Tertiary in age, are described as hornblende-andesite, augite-an- 

 desite, dacite, or quartziferous hornblende-andesite, and rhyolite or 

 quartziferous trachyte, together with basalt. The dacite followed the 

 hornblende-andesite, and the rhyolite the dacite, all of which in turn 

 are cut by the basalts. The rocks described as basalt vary greatly in 

 composition from the ordinary type of about 50 per cent, to over 60 

 per cent, of silica. These more silicious basalts are descirbed as desti- 

 tute of olivine. 



These igneous rocks do not appear to have come from central volcanic 

 vents, but have been erupted along great meridional lines of faulting, and 

 are often found bordering the uplifted blocks of Paleozoic sediments. 

 The chief localities of these rocks are along the east and west sides of 

 a great depressed block of Carboniferous strata, which is nearly sur- 

 rounded by outflows of Tertiary lavas. Among these are noticed great 

 numbers of local extrusions which are wholly independent at, the sur- 

 face, from neighboring masses. The whole condition of things suggests 

 forcibly that these great accumulations of Paleozoic strata are or were 

 immediately underlaid by a floor of crystalline rocks in a state of plas- 

 ticity. 



