196 University of California Publications in Geology [Vol. 10 



appear, and that the strata of both the Jacalitos and Etchegoin become 

 unfossiliferous. Also on attempting to trace the Glycimeris zone 

 southward from Coalinga it was lost within a few miles. Since no 

 unconformity has been discovered near the base of this zone, either 

 north or south of Coalinga or in Priest Valley, lithology and faunal 

 evidence must be relied upon for age determination. 



In large areas showing exposures of the lower Etchegoin as de- 

 scribed by Arnold and Anderson the sandstone has a gray or a striking 

 blue color. This has frequently been considered as being due to a 

 coating of sand grains by vivianite. These "vivianitic" sandstones 

 have frequently been considered characteristic of the lithology of the 

 lower Etchegoin, and mapping has been done on that basis. As sug- 

 gested by Arnold and Anderson, this horizon is not necessarily the 

 lowest occurrence of these beds. Thus in the southern part of the 

 Kreyenhagen Hills the strata known by their fossil contents to be of 

 Jacalitos age are of a bluish-gray color due to "vivianite." In the 

 Jacalitos Hills there is no change in lithology immediately below the 

 Glycimeris zone. Some distance north of the Coalinga area as mapped 

 by Arnold and Anderson the sandstone supposed to be characteristic 

 of the lower Etchegoin is absent. This also holds true for beds of 

 equivalent age in Priest Valley. 



In the period in which the geological work of Arnold and Anderson 

 was in progress the fauna of the Jacalitos was only imperfectly known. 

 More recent study by the writer 14 has shown that the fauna of these 

 beds is very similar to the fauna of the Etchegoin. Of the ninety- 

 three species known from the Jacalitos at the present time a very large 

 proportion, as shown by the accompanying table, are also found in 

 the Etchegoin. The number in common with the Santa Margarita is 

 shown to be small. An unconformity which occurs some distance 

 above the Glycimeris zone has been described by the writer. 15 It is also 

 shown that fresh-water beds occur in the lower part of the Etchegoin 

 of Arnold and Anderson in the Kettleman Hills. These beds are be- 

 lieved to represent the stage of the unconformity north of Coalinga. 

 The faunal break is not, however, greater than is to be expected 

 in a normal succession and does not appear to mark an important 

 separation. 



Nomland, J. O., Fauna of the Lower Pliocene on Jacalitos Creek and 

 Waltham Canon, Fresno County, California, Univ. Calif. Publ. Bull. Dept. Geol., 

 vol. 9, no. 14, 1916. 



is Nomland, J. O., The relation of the invertebrate to the vertebrate faunal 

 zones of the Jacalitos and Etchegoin formations of the Coalinga District, Univ. 

 Calif. Publ. Bull. Dept. Geol., vol. 9, no. 6, 1916. 



