1915] 



Clark: Fauna of the San Pablo Group 



433 



quite evident that the Etehegoin formation represents at least a considerable 

 part of the San Pablo, and as the Etehegoin lies well above the beds contain- 

 ing the Santa Margarita fossils it seems likely that the Santa Margarita 

 formation is in part of greater age than the San Pablo. (Bull. 396, p. 22). 



The new formation, described by Arnold 35 as the Jacalitos, out- 

 crops southwest of Coalinga in the vicinity of Jacalitos Creek, and 

 includes, in part at least, beds mapped as Coalinga by F. M. Ander- 

 son, to which reference has already been made. The Jacalitos, as 

 described, consists of a series of soft, indurated sandstones, gravels and 

 clays, about 3500 feet thick, resting upon a silicious shale lithologically 

 similar to the typical Monterey shale found throughout the Coast 

 Eanges. This shale was questionably referred to the Santa Margarita 

 by Arnold because, at one locality, he states that he found in sand- 

 stones below the shale, fossils which he referred to Tamiosoma gre- 

 garea and Trophon carisaensis and which he believed to be character- 

 istic of the Santa Margarita. 



The fauna from the upper part of Arnold's Jacalitos is very similar 

 to that of the Etehegoin and probably belongs to that series. But in 

 the lower part of the formation is a fauna which, as a whole, is some- 

 what different from that of the Etehegoin. 



Many geologists who have worked in the Coalinga field believe that 

 the shale mapped by Arnold as Santa Margarita ? is in reality Monte- 

 rey shale. The writer will not enter into this controversy, except to 

 state that it is still an open question. It is also thought by certain 

 palaeontologists that Arnold's belief that the Jacalitos fauna is dis- 

 tinct from that of the Santa Margarita was a mistaken one, and that 

 this fauna is merely a provincial phase of the' Santa Margarita, here- 

 tofore unknown. Professor J. P. Smith 30 evidently shared this belief 

 when, in his paper on the "Geologic Range of Miocene Invertebrate 

 Fossils," he divided the fauna of the upper Miocene into a lower 

 Santa Margarita — San Pablo zone, and an upper Etehegoin zone, 

 choosing not to recognize the Jacalitos. The writer will discuss the 

 probable position of the Jacalitos fauna later. 



In 1911 J. P. Smith 37 published a paper containing a correlation 

 table of the Neocene sections of California. He represented the Kirker 

 Pass section of the San Pablo as equivalent to the Santa Margarita 

 of Salinas Valley, and the San Pablo Bay section as equivalent to the 



35 Proc. Calif. Acad. Sci., 2d series Geol., vol. II, no. 2, p. 174, 1905. 



soProe. Calif. Acad. Sci., 4th series, vol. Ill, pp. 161-182. April 5, 1912. 



3t "The Geologic Record of California," Journ. Geol., vol. 18, no. 3, pp. 216- 

 227, 1911. 



