FAUNA OF TIJIC KNOXVHvLI-: SIOIMES. 201 



and the Shasta g'l'oup, but tliere is nothing- in the cliaracter of the other 

 four species of niolhisks from the auriferous shvtes which would render in- 

 consistent their reference to the age of the Knoxville beds. 



The specimens of Aucelhi and other auriferous shxte species just re- 

 fen-ed to were ol)tained by us from the rocks in phxce, those found near 

 the left l)ank of the Jlerced River, ^Mariposa County, Cal., about a quar- 

 ter of a mile below Benton's mills, I)eino- especially satisfactory as regards 

 both their [)Osition in the strata and their condition of preservation. Here 

 the strata have an almost vertical dip and they are plainly an integral part 

 of the great auriferous slate series. A part of our collection, as well as 

 some of those which were collected by King", Gabb, and Miss Erring- 

 ton, were obtained from within a few feet of the famous great quartz vein 

 which traverses the i\rariposa estate and whicli is inclosed in the aurifer- 

 ous slates. 



We did not obtain any Brleniniies from the auriferous slates, as King 

 and Gabb did, nor has Dr. White seen Gabb's B. pacificm, obtained from 

 this formation, but not figured. From the description it is supposed to be 

 identical with B. niacrifatis White,' obtained by Mr. Dall from Alaska and 

 found associated with an AiirHhi regarded as of the same species as A. 

 I^nbigtoiiU. and A. Piochii. 



That the Mariposa beds and tlie Knoxville beds are of the same age is 

 considered as proved b}' the identity of Aucella Piochii and A. Eniiiytonii, 

 sn])ported by the g-eneral character of the other fossils which tlie strata of 

 both respectively bear. It is true that this is the only specific identifica- 

 tion that has been made; 1)ut the species in question is one of extraordinarily 

 wide geographical range and it is also one of great constancy and exclu- 

 siveness as regards its distinguishing characteristics. 



Cei'tain of the species whicli characterize the strata of the Shasta 

 group in California have been recognized among the collections which have 

 been reported by different pei'sons from Washington Territory and British 

 Columbia, as well as from Alaska and the Aleutian Lslands. But none of 

 the species of that group has been found in any North American strata to 

 the eastward of the Pacific Coast region, if we except Greenland. While 



' See Bull. U. S. Geo]. Survey No. 4, p. 1^, PI. VI. 



