TEUCKEE CASOX. 831 



enormous fields of gray basalt, while to the north they connect with the 

 great body of trachyte, which overflows the Virginia Eange, extending 

 from the valley north of Spanish Peak across to Pyramid Lake; but whether 

 this normal sanidin-trachyte belongs to an earlier or later flow than the 

 trachytes at the head of Sheep Corral Canon has not been determined. 

 Lithologically, the trachytes of Clark's -Station are to be classed with the 

 true sanidin-trachytes of Washoe. 



Clark's Station is situated about midway in the Truckee Canon, in an 

 enclosed basin, shut in on all sides by eruptive masses. A mile to the west- 

 ward of the station, and at an elevation of about 4,300 feet above sea-level, 

 the basin is occupied by a series of soft white Pliocene sand-beds, which 

 overlie and "are more recent than the trachytes, rhyolites, and basalts. 

 They may be considered as marking the point of superior limit in the 

 deposition of Humboldt Pliocene beds in the Truckee Valley. From the 

 well-determined altitude of these beds in the Nevada Basin, it would seem 

 most probable that the lake-waters extended throughout the entire Truckee 

 Canon; that the valley of Glendale was a bay of the lake, receiving the 

 waters of the Truckee River somewhere in the region of Reno; but this 

 little group of Pliocene beds, which fills the valley near Clark's Station, is 

 the only relic of the formation in the canon, and either marks the limit of 

 deposition of the sediment, or else, as is most probable, that portion of the 

 deposit lying up the river from this point has been eroded, as it certainly 

 Las been for the lower 8 miles. The strata are quite horizontal, and are 

 largely made up of granitic materials, brought down, without doubt, from 

 the Sierra Nevada. They contain a few fragments of minute fresh-water 

 shells of the same species that are found in the Lower Truckee Valley. 



About 4 miles below Clark's Station, the canon widens out, leaving the 

 basaltic hills overlying the trachyte about a mile and one-half to the south 

 of the river. The open valley is occupied partly by trachytes and rhyolites 

 and in part by basalts, but largely by exposures of a decomposed older 

 rock, which is, with some hesitation, referred to propylite. It is of a dull 

 olive-^reen color, contains much carbonate of lime, is everywhere marked 

 by green, earthy masses the size of a pea, which appear to be decomposed 

 augite. Less decomposed passages occur here and there, with well-recog- 



