25G J. p. SMITH — AGE OF THE AUKIFEROUS SLATES. 



in Russia, and thinks that the time consumed in migrating from Russia 

 to America might explain its occurrence in Cretaceous rocks in America. 

 But now it becomes just as possible that they migrated the other way, 

 since we have Aucella in California in rocks of probably as great age as 

 any in Russia. In fact, it becomes more probable when we consider the 

 fact that in a country so near to Russia as England Aucella did not 

 appear until lower Portland time. 



Application of Neumayr's Theory of climatic Zones. 



M. Neumayr refers the Jura of California* and Nevada to the middle 

 European type, while admitting that there were some Arctic elements, 

 such as Aucella. The Jura of the Black Hills f he refers to the boreal 

 type, on account of the occurrence of Cardloceras. 



In a later work| Neumayr says that the California Jura shows a 

 commingling of boreal with temperate zone types, because the two 

 oceans joined in this region, and that it was separated from the Black 

 hills region by a strip of land. 



Professor Hyatt § has shown that the Upper Jura of Plumas county is 

 of central European type, and that it was separated from that of the 

 Black hills district. We have, then, in Calaveras and Mariposa counties 

 a boreal type of Jura about 160 miles south of a temperate zone type. 

 Something similar was recently observed by Dr A. Tornquist || in the 

 Jura of East Africa, where he found that the distribution of Jurassic 

 forms could not be explained upon the supposition of parallel climatic 

 zones, but rather upon the theory of separate provinces, that is, of more 

 or less separated sea-basins in which, individually, of course, climate 

 will show its effects. 



The Jura of Mariposa is boreal if that of the Black hills region is, for 

 it contains even more Arctic elements. 



Metamorphic Rocks of the Coast Range. 



J. D. Whitney^ considered the metamorphic series of the Coast range 

 to be of Cretaceous age from the supposed continuity of unaltered Creta- 

 ceous with the jaspers. 



Doctor Becker** followed Professor Whitney for the same reasons. 



* Ueber Klimatische Zonen wiihrenci der Jura und Kreide Zeit, Denks. K. Akad. Wiss., Wien, 1883, 

 p. 301. 

 fOp. eit.. p. 302. 



X " Die Geographisehe Verbreitung der Juraformation," Denk. K. Akad. Wiss., Wien, 1885, p. 12-i-5. 

 ? Bull, Geol. Soc. Am., vol. 3, p, 410. 



II Jahrb. Hamburg. Wiss. Anst. X 2, " Oxford fauna von Mtaru," p. 24. 

 ^ Geol. of California, vol. i, and "Auriferous Gravels." 

 ** Monograph XIH, U. S. Geol. Survey. 



