820 DESCRIPTIVE GEOLOGY. 



About 5 miles above Pyramid Lake, the Pliocene formation falls away, and 

 gives place to a Quarternary plain, which extends east and west, forming- 

 the shore-plain of both Pyramid and Winnemucca Lakes. As the river 

 cuts deeper into the Pliocene strata, near the point where it emerges on the 

 Quaternary plain, the material of the beds is found to be exceedingly coarse, 

 and cross-stratification quite common. The escai-pment of Pliocene form- 

 ing the east wall of the Quaternary Valley leaves the Truckee River, and 

 follows the Little Truckee toward Winnemucca Lake. About 2 miles 

 south of the lake, on the east bank of the river, occurs an interesting out- 

 crop of infusorial silica of the Miocene Tertiary, coming up unconformably 

 beneath the Pliocene. The latter are horizontal, while the infusorial beds 

 strike about true north, and dip to the eastward at an angle of 38°, forming 

 the steep river-bank, and probably continuing both under it and across it. 



Lithologically the upper beds of the infusorial deposit closely resemble 

 the same formation as already described in the Miocene series of Fossil Hill, 

 Kawsoh Mountains, and under the microscope reveal the same profusion of 

 siliceous JDiatomacea. 



Dr. C. G. Ehrenberg^ examined a large suite of specimens from this 

 locality, and has described in detail forty-six distinct forms, classifying 

 twenty-eight of them under Polijgastera and eighteen as FJiytolitharia. Of 

 these forms, the most abundant appear to be the same species as character- 

 ize the beds at Fossil Hill, namelv: 



Gallionella granulata. 

 GaUionella sculpta. 

 SpongolitMs acicularis. 



The lower portion of this seriep of beds becomes almost fissile in struct- 

 ure, and passes from pure white into bufi", brown, and chocolate-colored 

 beds. A few fragments of exogenous leaves and softer plant-stems are 

 observed, but nothing sufficiently characteristic was obtained to aid in deter- 

 mining the age of the formation, although careful search might result in 

 rich and important collections. The most extreme product of alteration of 

 these infusorial beds is a gray flinty stratum having almost the look of 



^tTber die wachseude Keuutniss des unsichtbaren Lebeus als felsbildende Bacil- 

 larieu in Californien, Berlin, 1870, 19, 



