CHICO AND HOKSETOWN FAUNAS. 445 



in the Sacramento valley, and that the advancing shore of the trans- 

 gressing sea furnished a uniformly favorable habitat for its littoral fauna. 



The lists of the more important fossils given in the tabular descriptions 

 of sections on Cottonwood and Elder creeks show that the Chico fauna 

 ranges through nearly 4,000 feet of strata. 



A few of the species in the lower half of the Chico are worthy of spe- 

 cial mention. The occurrence of CoralHochama orcutti at about the same 

 horizon in all the sections examined fixes the position of the Wallala 

 beds in the lower part of the Chico. 



The following occur also in the Horsetown beds, some of them ranging 

 down to the base of that division : 



Pecten opercuUfonnis. Meekia sella. 



Exogyra parasitica. Chione varians. 



CacuUxa truncata. Lunatia avellana. 



Nemodon vancouvererms. Ammonites {Desmoceras) hoffmannl. 



Trigonia leana. Ammonites {Desmoceras) sp. a. 



Trigonia vequicostata (?) 



' HORSETO IV N FAUNAS. 



Upper Horsetown. — In the sections described the very close connection 

 of the Chico with the preceding Horsetown fauna is not fully shown, 

 because the upper part of the Horsetown beds is not very fossiliferous 

 along the measured sections. At Horsetown and Texas springs, how- 

 ever, only a few miles northeast of the Cottonwood section many fossils 

 have been found that evidently belong very near the top of the Horse- 

 town beds. Lists of species from these localities showing a commingling 

 of the Horsetown and Chico faunas have already been published."^ The 

 collections of the past season at these places have added three interesting 

 species of ammonites, viz : Lytoceras sacya, Forbes, which is evidently 

 identical with the Queen Charlotte specimens referred to that species ; a 

 Desmoceras (the same as the one in the Chico listed as Ammonites {Desmo- 

 ceras), sp. a), that seems rcferal)le to Desmoceras beadanti, Brongiart, which 

 also occurs in the Queen Charlotte formation; and an Acanthoceras that 

 resembles one of the forms of Acanthoceras mammillare, Schloth., figured 

 by d'Orbigny.f In connection with these species the Schloenbachla in- 

 flata, Sowerby, from the top of the Horsetown on Cottonwood creek may 

 be mentioned. This species is reported from the Queen Charlotte forma- 

 tion and it occurs in the Ootatoor group of southern India. Stoliczka's 

 figure J seems to agree in every particular with our California specimen 

 which was found associated with two Chico species only a short distance 

 below the assumed base of the Chico. These ammonites, together with 



♦Bull. Geol. Soc. of Am., vol. 4, pp. 210, 250. 

 tPal. Francaise Terr. Cr6tac^, t. 1, pi. 73. 

 t Palaeontologia Indica, vol. 1, pi. 27. 



