ABSTRACTS OF PAPERS 229 



Lorenzo formation of Arnold and Hannibal. Some of these common forms 

 are fairly highly ornamented gastropods, and it might be expected that they 

 would have a rather limited geologic range. It should be remembered, how- 

 ever, that the work of describing the faunas of the Oligocene has only begun 

 and the range of many of the described species has not been established for a 

 certainty. For this reason the writer hesitates to say that the Agasoma gravi- 

 dum beds are certainly as old as the Lincoln beds of Weaver, but there seems 

 to be no doubt that they belong to the same general period of deposition, if 

 not to the same faunal horizon. The San Lorenzo formation in the region of 

 the Santa Cruz Mountains, described and referred to the Oligocene by Dr. 

 Ralph Arnold, belongs to this same period, as do also the Kreyenhagen shales 

 recently described by Robert Anderson and Robert W. Pack and referred tenta- 

 tively to the Oligocene.^ 



Sufficient faunal evidence has now been obtained to show that these shales 

 belong to the Astoria series. The Astoria series is also known to be repre- 

 sented by beds at the south end of the San Joaquin Valley in the San Emigdeo 

 Hills. In this general locality the Oligocene strata are separated from those 

 of the Miocene (Monterey group) by volcanics of considerable thickness. 



FAUNA OF THE ETCHEGOIN PLIOCENE OF MIDDLE CALIFORNIA 

 BY J. 0. NOMLAND 



(Abstract) 



Results of studies on the Etchegoin Pliocene in the region of Coalinga, Cali- 

 fornia, may be summarized as follows : 



1. Pliocene sediments have accumulated to the thickness of over 10,000 feet 

 in this area under shallow marine or terrestrial conditions. 



2. While marine accumulation prevailed the floor of the basin of deposition 

 was raised locally several times above sealevel; after terrestrial conditions 

 became predominant brief periods of marine deposition occurred. 



3. In post-Pliocene time diastrophic movements of great magnitude occurred 

 in the Coalinga region. 



4. The strata above the Santa Margarita (?) and below the Tulare belong to 

 one period of deposition. 



5. The Santa Margarita-San Pablo fauna is distinctly different from that of 

 the Etchegoin. 



6. As shown by the invei-tebrate and vertebrate faunas, the whole Etchegoin 

 is of Pliocene age. 



7. An unconformity in the lower part of the section heretofore grouped with 

 the Etchegoin southeast of Coalinga is probably the line of division separating 

 the Etchegoin from the Santa Margarita (?) 



8. An unconformity above the "Glycimeris zone" in the Etchegoin north of 

 Coalinga is probably only of local importance. 



9. Four distinct faunal zones have been recognized in the Etchegoin forma- 

 tion. 



^ Robert Anderson and R. W. Pack : Geology and oil resources of the west border of 

 the San Joaquin Valley north of Coalinga, California. Bull. U. S. Geol. Survey, no. 603, 

 1915, pp. 77-78. 



