1916] Martin: Pliocene of Middle and Northern California 247 



Near the mouth of Elk River both of these horizons are very 

 fossiliferous. In the lower beds the fossils occur in numerous hard 

 concretions, while in the overlying sands they occur in a thick mass 

 as an unconsolidated shell bed. The faunas are sufficiently distinct 

 to allow the series to be separated into two horizons, although they 

 are not separated by a stratigraphic break. From the great number 

 of Eecent species found in the upper horizon it seems certain that 

 it is very closely related to the Upper San Pedro Series, at San 

 Pedro, and is at least Pleistocene in age. The underlying beds also 

 contain a large number of Recent forms, but they likewise contain 

 a large number of spcies that are common to the Merced and the 

 Wildcat Series, and it is not improbable that this lower horizon rep- 

 resents very late Pliocene and is to be correlated with the upper- 

 most part of the Wildcat Series. 



Along the summit of the cliff one quarter of a mile southeast of 

 Cape Blanco there is a formation of gray sand, mudstone, and gravel 

 lying horizontally across the tilted edges of the Empire Formation. 

 At the base of this deposit there is a fossil bed containing fifteen or 

 twenty species, all of which appear to be Recent. A number of these 

 are species of clams which bury themselves in the mud, such as 

 Schizothaerus nuttalli Conrad. These fossils are, at the present 

 time, imbedded in the uppermost part of the Empire Beds instead of 

 the more recent deposit. This formation is hardly more than ten or 

 fifteen feet in thickness and is overlain by three or four feet of soil. 

 Diller considered these beds to be a part of the Pleistocene deposits 

 at the mouth of Elk River, the Elk River Beds. There are a few 

 species in each of these localities which are not common to both. 

 The difference in the faunas may be due to the difference in position 

 with regard to the strand line. The formation at the top of the cliff 

 near Cape Blanco was undoubtedly deposited after the coastal plain 

 had been formed, and just previous to its uprising. It is probable 

 that the major part of the Elk River Beds were deposited during 

 the period in which the coastal plain was forming, and in this way the 

 beds at the mouth of Elk River would antedate the formation uncon- 

 formably overlying the Empire Formation near Cape Blanco. 



Correlation 



The physical features of the formations, with which we are deal- 

 ing, have been briefly outlined, and complete faunal lists from all of 



