204 QUICKSILVER DEPOSITS OP THE PACIFIC SLOPE. 



The age of the ^4.vtY'//cj!-bearing' beds, whether in Cahfornia or else- 

 where, is not fnlly determined, apparently on acconnt of the eqnivocal char- 

 acter of the faunas associated with this fossil. 



Pxith Eichwald and Whiteaves contend that all the strata which bear 

 Aucclla co)/r(')itric(i and A. niosqiicnsis are certainly of Neocomian age. On 

 the other hand, Keyserling, Trautschold, D'Orbigny, and others as confi- 

 dently assert that the}' are of Jurassic age and many jialeontologists have 

 hitherto regarded Aucella as an exclusively Jurassic geinis. Even so late 

 as the year ISSl Mr. A. Pavlow, a member of the official geological com- 

 mission of Tvussin, placed in the Jurassic scries the well known strata which 

 in eastern and other parts of Russia hear A accJhc coi/rciUrica, as the earlier 

 Russian geologists also did.' 



Dr. AVhite thinks it not impossible that Aucella occurs in the Jurassic 

 in some regions and in the Neocomian in others, just as a number of Lower 

 Carboniferous species of Europe are found in the Upper Carboniferous of 

 North America and as certain species are known to pass from the Devonian 

 to the Carboniferous, lie inclines, however, to the opinion that the Cali- 

 fornia occurrences are referable to the Lower Neocomian, which, as has 

 been seen, is substantially the result at which Gabb arrived for the group 

 here called the Knoxville series. 



As has been seen, the age of the metamorphic series of the Coast 

 Ranges (which is that most usually associated with the quicksilver deposits), 

 the age of a highly important portion of the auriferous slates of California, 

 and consequently also the structural relations of the Coast Ranges and Sierra 

 Nevada depend almost entirely upon two closely allied species, or on two 

 varieties of a single species, oi Aucella. The very great importance which 

 this fossil thus acquires is much increased by the fact that it occurs along 

 the Pacific Coast at various points up to Alaska, a distance of about two 

 thousand miles, and again at very widel}' separated points in Europe. 



Tn the hope that it may lead to a more extended knowledge of the 

 distribution of this peculiar and important fossil, I have induced Dr. White 

 to prepare a description, with illustrations, of Aucella, which appears as an 

 appendix to lliis chapter. 



' See Bull. Soc. g^ologique France, :i(l series, vol. 12, 1884, pp. 686-696. 



