50 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



species. In this respect it resembles other locaHties within 

 the borders of the Great Valley. The succession of disturb- 

 ances inaugurating the Chico was here so little felt as to 

 allow pre-existing species to survive locally. The Chico 

 faceies of this locality, is, however, represented by such 

 forms as Pachydiscus newberryanus., P. suciaensis, Baculites 

 chico'ensis, Cinulia obliqtia, and also Placenticeras califor- 

 niaini and P. facijicwn have been found elsewhere in 

 undoubted Chico deposits, and they have been found in no 

 other deposits. The former occurs in the Lower Chico 

 beds of the Forty-nine Mine, Jackson County, Oregon, and 

 in exactly the same horizon at Henley, Siskiyou County, 

 California, along with P. pacificum; while Dr. J. P. Smith 

 states that P. californicum has been found in the Lower 

 Chico of the San Fernando Mountains, Los Angeles 

 County, California, and that Mr. F. Rolfe has found in 

 the Lower Chico of Silverado Canyon, Orange County, 

 California, P. pacijiacni associated with typical fossils of 

 this epoch. 



2. The Chico-Knoxville Unconformity. 



This occurrence of Lower Chico strata seems the more 

 important because upon the northern flanks of Mount 

 Diablo, only a few miles away, Chico beds are found 

 apparently conformable upon AucclIa-hediYmg shales form- 

 ing a series of several thousand feet in thickness. These 

 Mount Diablo deposits were first described by H. W. Tur- 

 ner (1891) and afterward discussed by Stanton (1895, 

 p. 21, etc.). Mr. Turner believed that a portion of this 

 conformable series represented the Horsetown, but was 

 unable to prove it to his own satisfaction. The upper por- 

 tion of the series has yielded Baculites chicoensis and a few 

 other Chico forms, and the lower portion is the horizon of 

 the Knoxville discussed a few pages back. Stanton esti- 

 mated that the intervening strata had a thickness of about 

 five thousand feet, in regard to which he says: "If the 

 horizons are all represented, then sedimentation was here 

 very much less rapid during a part of the Cretaceous 



