304 J. S. DILLER — GEOLOGY OF THE TAYLORVILLE REGION. 



Among the eruptives there is great variety. Their extravasation, be- 

 ginning early in the Paleozoic, recurred vigorously in the Triassic and at 

 the close of the Jurassic, and. finally, also in the Neocene and Pleistocene. 



The dioritic rocks of the region are a portion of the great granitoid 

 mass of the upper Sierra Nevada, and are evidently eruptive, with well 

 denned contact phenomena in Triassic formations. Their eruption is 

 certainly post-Triassic * and may have taken place immediately at its 

 close or after the deposition of the Jurassic. 



There are at least four unconformities in the geologic column of the 

 Tavlorvillc region. Designated by the horizons between which they 

 occur, they are as follows: Pleistocene-Neocene, Neocene-Jura. Jura- 

 Trias, Trias-( !arboniferous. 



During the greater part, if not the whole, of the Paleozoic the sea 

 covered the region now occupied by the northern portion of the Sierra 

 Nevada. 



The great disturbance at the close of the ( larboniferous may have been 

 accompanied by an uplift, forming land during the early Triassic: hut if so, 

 it subsided and was ready to receive the deposits of the upper Triassic. 



The disturbance at the close of the Triassic formed no land in the north- 

 ern Sierra region, hut that which closed the Jurassic was accompanied by 

 a great upheaval, excluding the sea to the western base of the Sierras. 



The general structure of the Tavlorvillc region involves a synclinal 

 and two limiting anticlinals. 



After the folds were overturned toward the northeast, the Grizzly anti- 

 clinal was affected by an overthrust fault in the same direction. The 

 throw along this fault in the older strata is so much greater than in those 

 of Jurassic age as to suggest that a large part of the displacement took 

 place at the close of the Triassic and Avas followed by movement on the 

 same plane at the close of the Jurassic. 



* On this point see also"Notes mi the Early Cretai ns of California and Oregon," by G. F. 



Becker: Mull. Geol. Soc. Am., vol. -. p. 20G. 



