202 G. F. BECKER — EARLY CRETACEOUS OF CALIFORNIA. 



comian and the Shasta county series to the Gault. * These strata were 

 again studied in connection with an investigation of the quicksilver deposits 

 of the coast by Dr. White and myself. The J.wee//a-bearing beds of the 

 gold belt in the Sierra Nevada of California were identified with those of 

 the Coast ranges, which we called the Knoxville group, and all of them were 

 considered equivalent to the Alaskan ^.ttce^^a-bearing strata, the paleontology 

 of which Dr. White has studied, and they were referred to the Neocoraian 

 with a slight doubt whether they might not be the latest Jurassic rather 

 than the earliest Cretaceous. Dr. White made it clear that Aucella is both 

 a Jurassic and a Cretaceous fossil, and in his discussion of its occurrence he 

 showed that its apparent age is younger toward the edges of its area of dis- 

 tribution, f We considered the Horsetown group as seemingly younger than 

 the Aucella beds, and Dr. White agreed in its probable reference to the 

 Gault ; but, like Gabb and AVhitney, we found no thoroughly satisfactory 

 means of making a comparison. The Horsetown beds lie unconformably 

 upon a mass of nearly vertical slates, as was stated with reservations by 

 Whitney and confirmed without reservation by myself, and it seemed possible 

 that this non-conformity also divided the Knoxville beds from those of Horse- 

 town. It was also considered possible that the non-conformity represented a 

 pre-Cretaceous upheaval, suspected on other grounds, but unproved. The 

 tendency of our researches was thus rather to emphasize the supposed differ- 

 ence in age between the Knoxville and Horsetown groups, while no final 

 conclusion was reached as to their relations. % 



Contemporaneously with the publication of these views Mr. J. Lahusen 

 issued a monograph on Aucella in which he also followed this genus from 

 about the middle of the Jurassic (the Oxfordian) upward into the Creta- 

 ceous. § His views seem to me substantially the same as White's, except- 

 ing that he discriminates numerous species in the genus while White tends 

 strongly to regard the many modifications of this mollusk as mere varieties 

 of a single species. The last contribution to the subject is by Mr. Whiteaves, 

 who, from a study of the lower Cretaceous fauna of British Columbia in 

 comparison with that of the Queen Charlotte's islands, has reached the con- 

 clusion that all of the Aucella-hQQ.v\r\g beds of that region are the homotaxial, 

 though not necessarily the contemporaneous equivalents of the European 

 Gault. II I was not aware of Whiteaves' latest views when I made the ob- 

 servations to be recorded in this paper. 



Importance of the Subject — The subject of the age of the members of the 

 Shasta group is one of great importance to California geology. The Knox- 

 ville beds of the Coast ranges are those which are so extensively metamor- 



* Trans. Roy. Soc. of Canada, vol. I, § 4, 1882, p. 85. 



t Mr. A. Pavlow had previously su^K^sted that the Russian species of Aucella were derived from 

 the north, ns i.s mentioned hy I)r. White. 

 X Geology of tht- Quicksilver Deposits of the Pacific Slope, 1888, chapter 5. 

 g Ueber die Kussi^chen Aucellen, St. Petersburg, 18S8. 

 II Contributions to Canadian Paleontology, part II, 1889, p. 153. 



