70 GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



"This species, Melosira granulata, is synonymous with Ehrenberg's Gallionella 

 granulata, and other synonyms for the species are Melosira punctata, Gallionella 

 marchica, G. procera, and G. tenerrima. 



"I can discover no species in the material sent me which would limit the deposit 

 to the Miocene age, for the most abundant form, M. granulata, is living to-day in 

 the Para River, South America, and elsewhere, as well as occurring fossil in 

 Tertiary deposits. 



"There is nothing to prevent this deposit from being regarded as Pliocene if 

 stratigraphical evidence warrants this view, but the deposit was laid dow-n in fresh 

 water. In addition to the two species above given there are a few forms of Coscino- 

 dlscus radiatm." 



COMPARISON OK SIEBERT TUFFS WITH MIOCENE PAH-UTE LAKE DEPOSITS. 



Miocene deposits have been described b3' King in western Nevada" between 

 the one hundred and seventeenth meridian and the Sierra Nevada. These deposits 

 are always upturned, dipping from 10 to 25, and they are frequently cut through 

 and overflowed by basalt. They are usually made up of volcanic materials, and 

 are several thousand feet thick. They contain beds of white and yellow infusorial 

 silica, and on the northeast point of the Kawsoh Mountains, where the strata are 

 tilted, eroded, and covered by caps of basaltic rock (as on Siebert Mountain in 

 Tonapah), the following species were most abundant: 



Gallionella granulata. 

 Gallionella sculpta. 

 Spongolithis acicularis. 



These also were recognized: 



Pinnubaria ilia-quails, and 

 Coscinodiscus radiatus. 



The age of these beds is determined more especially by molluscan and 

 mammalian fossils, found elsewhere. 



These beds, therefore, are of the same character as the Siebert tuff at 

 Tonopah, which was deposited in the rhyolite-dacite period, and suggest that 

 the lake in which the tuffs were deposited is identical with the Miocene Pah-Ute 

 Lake of King. 6 The tilting and amount of erosion of the Tonopiih white tuffs 

 prevents any correlation with the Pliocene lake (Lake Shoshone)'' beds, whose 

 distribution frequently bears a close relation to the present topographic basins, 

 and which are little disturbed. 



a U.S. Geol. Expl. Fortieth Har., vol. 1, p. 412etseq. l> Op. cit., p. 454. cOp. cit.. p. 466. 



