OPINIONS OF PREVIOUS WRITERS. 245 



of A. piochi, and that the Auriferous slates are possibly Tithonian, a 

 transition from Jura to Cretaceous. 



1880. On page 39 of "Auriferous Gravels of the Sierra Nevada of 

 California," J. D. Whitney outlines the Auriferous slates as " all the 

 metamorphic sedimentary rocks of the Sierras," and says that they 

 are of both Triassic and Jurassic age, but that none are Cretaceous, for 

 rocks of that age lie unconformably on the metamorphic series. He 

 thinks also that it is doubtful whether there are any Paleozoic rocks in 

 the series, for there is no proof that the limestones of the Auriferous 

 slates are a continuation of those in Shasta and Butte counties. Professor 

 Whitney also gives a section of the Auriferous slates, in which he divides 

 them into two great divisions : the upper containing the Mariposa slates 

 and diabase-tuff, and the lower containing mica-schists and limestones' 

 which may be equivalent to those at Pentz ranch, Butte county, and 

 therefore Carboniferous. 



1883. J. Marcou ^ says the Mariposa slates are Triassic in age, and 

 that they belong to the Rhetic, or zone of Avicida contorta ; also that 

 Ammonites colfaxi is ©f Triassic type. 



1884. J. F. Whiteaves j says that certain so-called Jurassic rocks (i. e., 

 the Mariposa slates) may be Cretaceous and not Jura. The same he 

 thinks is true of the Jura of the Black hills, and most of the other so- 

 called Jura in the west. 



1885. C. A. White X says that Amelia erringtoni and A. piochi are 

 equivalent, and that part of the Auriferous slates are thus of Knoxville 

 (Neocomian) age. Another part he thinks may be of Paleozoic age. He 

 concludes that if all the Aucella-bearing rocks are Neocomian there is 

 probably no Jura in California, as all the so-called Jura is probably 

 equivalent. 



1886. J. S. Diller§ says that the auriferous slates are part Carbonifer- 

 ous and part Mesozoic. 



1888. G. F. Becker II discusses the relations of the Mariposa slates to 

 the Knoxville, and concludes they are identical, because of the sup- 

 posed identity of Aucella erringtoai and A. piochiy no other supposed 

 Shasta species being found in the Mariposa slates. Doctor White If 

 discusses the age of the Aucella-bearing beds of the Coast range, classes 

 them with the Neocomian, and says that the Aucella beds of the Aurif- 

 erous series — that is, the Mariposa slates — are their equivalents. 



* Bull. Soc. Geol. France, 188:3, p. 410. 



tGeol. Survey Canada, Mesozoic Fossils, vol. i, part iii, pp. 200-201. 



J Bull. 15, U. S. Geol. Survey, pp. 24-20. 



§ Bull. 33, U. S. Geol. Survey, p. IG. 



II Monograph xiii, U. S. Geol. Survey, pp. 198-204. 



^ Monograph xiii, U. S. Geol. Survey, Appendix to chapter v. 



