230 QUICKSILVER DEPOSITS OF THE rACIFIC SLOPE. 



We do not yet know euoiigli of the general geology of Alaska to speak confidently 

 of the stratigraphical relations of the .-iHre/Za bearing strata there; bnt there seems 

 now to be no reason to doubt that all such strata in other parts of western North 

 America oughC to be referred to the opening epoch of the Cretaceous. I do not think, 

 however, that the question of the exact geological age of these strata is of great im- 

 portance in this connection, but no reasonable doubt can be entertained that a large 

 proportion of the discoveries of AiiceUd have been made iu strata of unquestionably 

 Cretaceous age. 



In the year 1864 Jlr. William M. Gabb published specimens of AitccUa from two 

 separate localities iu California and, as was then supposed, from two separate forma 

 Mons. The first of these was published under the name of Inocerumus riochii' and 

 the other under the name of Lima Erringtonil.- The first-mentioned fossils were 

 afterward published by hiui as Aucclla Piochii,^ and Mr. Meek afterward republished 

 and illustrated the others under the name of Aucella Erringfonii.* Mr. Gabb never 

 doubted the Cretaceous age of the first mentioned forms; but it seems that he 

 regarded the strata from which came his Lima Erringtonii as of Jurassic age. Mr. 

 Meek agreed with him in this respect, as did also other authors. 



Upon an examination of the collections made in California by the division of the 

 LT. S. Geological Survey in charge of Dr. Becker, which wore submitted to me in 1884, 

 I became satisfied that the AiiceUa riochii and ^1. Erringtonii of Gabb belong to one 

 and the same species and that that species was no other than the one which had long 

 been known under the various names of A. concentrica, A. mosqucnsis, A. pallasii, A. 

 erassicoUis, etc. (see Hull. U. S. Geol. Survey No. 15, p. 2.3). 



As Aucella Erringtonii was obtained from the auriferous slate series iu California, 

 this conclusion of course involved the opinion that at least a part of that series is 

 equivalent to the Knoxville division of the Shasta group, and therefore of Creta- 

 ceous age. This conclusion was supported by the personal discovery iu the auriferous 

 slates of the Mariposa estate, in company with Dr. Becker and his assistant, Mr. Turner, 

 of specimens oi Aui-ella that are phiinly identical with the ^4. Piochii of Gabb, which is 

 found abundantly in the Knoxville division of the Shasta group. These and other facts 

 bearing upon the relations of the A«ce??rt-bearing strata of different districts in Cali- 

 fornia are discussed by myself in Bulletin No. 15 of the LT. S. Geological Survey and 

 by Dr. Becker in Bulletin No. 10. So far as I am aware, no other forms than those 

 mentioned iu this article are properly referable to the genus Aucclla. It is plain that 

 neither the ^1. contracta nor the A. impressa of Quenstedt l)elougs to this genus.^ It is 

 also evident that the greater part of the species which Stoliczka ranged under the 

 genus Aucella were not intentionally so placed by h\m.'^ 



EXPLANATION OF THE PLATES AND COMMENTS. 



Iu the foregoing paragraphs I have expressed serious doubt whether more than 

 one clearly definable species of Aucella is yet known, at least in the northern hemi- 



1 Geol. Survey California, Palieontology, vol. 1, 1864, p. 187, PI. 25, Figs. 173, 174. 



• Proc. California Acad. Nat. Sci., vol. 3, 1868, p. 17.3. 



3 Geol. .Survey California, PaUrontology, vol. 2, 1809, p. 194, PI. 32, Fig. 92, <i, h, c. 



<Geol. Survey California, Geology, vol. 1, 186.'), pp. 479, 480, PI. I, Figs. 1,2,3,4, and 5. 



'' Der Jura, p. 501, PI. 67, Fig. 2, and p. iJ32, PI. 73, Fi^'. 47. 



"Pal. ludica, vol. 3, index, p. 513. 



