Geol— Vol. II.] ANDERSON— CRETACEOUS DEPOSITS. 43 



hand, many important species run through the whole of the 

 Horsetown, forming connecting Hnks from bottom to top. 



In the basin of the Sacramento the base of the -Horse- 

 town division of the Cretaceous has perhaps been well 

 placed at the upper limit of the range of Aucella. Few if 

 any of the species characteristic of the Horsetown appear 

 to extend below this limit, and until this supposition shall be 

 proved erroneous the boundary seems to be a practical one. 

 It is stated by Diller and Stanton (1894, p. 446) that many 

 well known and typical Horsetown species occur within a 

 few hundred feet, stratigraphically, of the upper range of 

 Aucella, near the Elder Creek section. Below this point, 

 however, as one descends the series, they entirely disappear 

 or have not been found. Or, with the exception of Belem- 

 nites impressus, Lytoceras batesi, Crioceras latum, and two 

 or three others, there are perhaps no species connecting the 

 Horsetown faunally with the strata containing Aucella, 

 while on the other hand, the associates of this genus form a 

 separate and distinct fauna. 



The Pa sk cut a Hoi'izon. 



The strata containing Aucella, that is, Knoxville, as 

 originally understood, have been made the subject of a 

 special faunal study by Dr. Stanton (1895) who has pub- 

 lished a somewhat complete list, containing in all about 

 seventy-seven species, fifty of which are described as 

 new. He remarks that the majority of this number are 

 rare; yet even so, this is an unexpectedly large number 

 when contrasted with the few species that had formerly 

 been known from the Knoxville. Yet had this assemblage 

 of species been found distributed throughout the twenty 

 thousand feet of strata that have been referred to the 

 Knoxville, it would not have seemed surprising, for this 

 thickness of strata is twice as great as the entire sum of the 

 Horsetown and Chico strata combined. But the most inter- 

 esting part of this discovery is not the large number of 

 Knoxville species brought to light, but the fact that they 

 were nearly all obtained, not from the entire range of twenty 



