Crandall — Santa Clara Valley Region %n California,. 37 



The following are characteristic Chico forms : 



Anchura californica 

 Baculites chicoensis 

 Nautilus sp. 

 Pinna Br ewer i 



The Chico series is composed of dark shales, like those of 

 the Knoxville, with sandy and calcareous layers. These cannlo 

 be distinguished from the lower series except by the fossist. 

 The fossils occur sparingly through the beds, northeast, east, 

 southeast, and south of Diablo ; but the only place where they 

 are abundant is at Curry's Creek. Besides the shales, at Curry's 

 there are conglomerates, the pebbles of which are fragments of 

 metamorphic rocks and quartz porphyry. 



In a geologic section, Mr. Turner shows the Chico resting 

 unconformably upon the Franciscan, but at a very high angle, 

 and overlain at this place by Eocene beds. In another section 

 the Chico rests upon the Knoxville, with dips apparently con- 

 formable ; but he says that there is no doubt that a considerable 

 time elapsed between the close of the Knoxville epoch and the 

 opening of the Chico epoch. The probable thickness of the 

 Chico, Mr. Turner gives as about six thousand feet.* 



Hayioards. — A specimeu of Crioceras percostatum Gabb is 

 given by Andersonf as having been found near Haywards, but 

 from a locality that is unknown. It is considered by him 

 as probably representing the Knoxville at this place. In the 

 first part of his paper he has given this form as a typical 

 Horsetown form.:}: Gabb has classed it as belonging to division 

 " A," which does not place it definitely. § In connection with 

 other forms at nearby localities, it will be considered here as a 

 Horsetown form. 



East of Decoto. — In the collection of the University of Cali- 

 fornia there are two specimens of Aucella Piochi Gabb, marked : 

 " east of Decoto." The exact locality is not known, but it prob- 

 ably is in the southeast corner of the Concord sheet, northwest 

 of and adjoining the Pleasanton region. 



Pleasanton region. — The Cretaceous of the Pleasanton region 

 covers a large area, which includes about one-sixth of the topo- 

 graphic sheet of this name. Sunol, Pleasanton, and Walpert 

 ridges are for the most part composed of Cretaceous beds. From 

 these beds there has been collected a specimen of Venus varians 

 Gabb, of the Horsetown, and several Knoxville forms ; Aucella 

 crassicollis Keyserling, Aucella Piochi Gabb, and Ammonites 

 3 sp. iudet. The Tertiary overlies the Cretaceous on the west 



*H. W. Turner, Geology of Mt. Diablo, Bull. Geol. Soc. Am., ii, 395. 

 f Cretaceous Deposits, Proc. Cal. Acad. Sci., 3d series, ii, No. 1, 45. 

 % Loc. cit. p. 42. §Pal. Cal., i, 77. 



