INTERGRADATION OF THE SHASTA AND CHICO. 211 



" This collection leaves no room for doubt that the faunas of the Shasta and Chico 

 groups are so intimately blended that they cannot be separated. Horsetown is a 

 well known Shasta locality, from which the types of some of Gabb's Shasta species 

 were collected, yet in this small collection, containing twenty-one species from this 

 place, ten species belong to the Chico fauna as described by Mr Gabb. Combin- 

 ing the collections from these localities, there are thirty-six species enumerated, of 

 which ten have been described as coming from the Shasta group, eighteen from the 

 Chico group, and eight are doubtful or undecided." * 



So far as I have been able to learn, about seventy species and a dozen 

 genera not represented by determinable species have already been rec- 

 ognized in the Shasta series of California. Of these fossils certainly more 

 than one-fourth, and probably nearly one-half, continue upward into 

 the Chico beds, and clearly indicate that the Horsetown and Chico beds 

 are much more closely related than has been supposed. f 



When we take into consideration, at the same time, both the strati- 

 graphic and faunal evidence, there can be no doubt that the Horsetown 

 and Chico beds were formed in one period of continuous sedimenta- 

 tion. 



Relation of the Horsetown and Knoxville Beds. — In Tehama county, Cal- 

 ifornia, where the contact between the Horsetown and Knoxville beds 

 is well exposed, their relation can be studied to great advantage. Along 

 Elder creek, just north of the fortieth parallel, at the eastern base of 

 Yallo Bally, the unaltered fossiliferous Cretaceous strata have an appar- 

 ent thickness of nearly 30,000 feet.J The whole series, including the 

 Chico and Shasta groups, dips eastward away from the Coast range with 

 remarkable uniformity and appears to he one continuous series of sedi- 

 ments from top to bottom without a perceptible interruption. In the 

 lower 19,900 feet its only fossil found is Aucella. These sedimentary rocks; 

 the Knoxville beds, are limited below by serpentines resulting from the 

 alteration of peridotitic eruptives such as form a considerable portion of 

 the Klamath mountains and Coast range. In the upper 3,900 feet of the 

 Elder creek section Chico fossils occur abundantly, while in the inter- 

 mediate 6,100 feet Horsetown fossils have been found. The latter are 

 best exposed in the Eald hills between Paskenta and Lowrey's, where 

 Aucella occurs abundantly in the basal portion, associated with Ammon- 

 ites batesii, Trask ; A. ramosus, Meek.; A. traskii (?), Gabb; Ancyloceras 

 percostatus, Gabb ; Rhynchonella, n. sp. ; Siliqua, sp. undet. Although 

 these fossils were not actually seen together with Aucella in the same 

 rock exposure, yet they were seen so near together throughout a great 



* See also Mr Stanton's paper which immediately follows, p. '22.',, et seq. 



fjt is important to rememlier in this connection that the collections have been made almost 

 wholly by geologists while studying the stratigraphy, and not by paleontologists who were en- 

 deavoring to determine the relations of the faunas. 



J; Am. Jour. Sci., 3d ser., vol. xl, 1890, p. 47<>. See also Bull. Geol. Soc. Am., vol. 2, p. '_'n7. 



