1917] Nomland: The Etchegoin Pliocene of Middle California 193 



tension of our knowledge of the stratigraphy and palaeontology of 

 this system it therefore becomes important to make a detailed study 

 of the successive faunal zones in the most complete section known. 

 Aside from the importance of finding horizons bearing vertebrate 

 remains in the same section with those containing marine forms, it is 

 evident that the sequence at Coalinga is the most important in middle 

 California. The strata have been much folded, due to important dias- 

 trophic movements in post-Pliocene time. Extensive outcrops of the 

 Pliocene south of Coalinga show exposures aggregating over ten 

 thousand feet of strata, this being the greatest thickness of sediments 

 belonging to this period described in America. 



In the mapping of the Coalinga district by the members of the 

 United States Geological Survey the " Jacalitos" formation was desig- 

 nated as a separate unit. A more extensive faunal and stratigraphic 

 study has shown that the "Jacalitos" and the Etchegoin beds are 

 closely linked in diastrophic history, and the former has therefore 

 been included as a lower part of the Etchegoin in the present paper. 

 The whole Etchegoin, contrary to the practice of many earlier geolo- 

 gists, is here placed in the Pliocene. 



During the progress of the study of this problem the writer has 

 frequently received the criticism and advice of Professor J. C. Mer- 

 riam. The assistance derived from simultaneous study by him of the 

 vertebrate material from Coalinga has been very valuable. Much 

 help and encouragement both in the field and in the laboratory have 

 been given by Dr. B. L. Clark, Instructor in Palaeontology at the 

 University of California. The writer is indebted to Mr. R. W. Pack 

 of the United States Geological Survey for information concerning the 

 location of numerous excellent fossil localities in the lower Etchegoin. 



PREVIOUS WORK 



The Etchegoin beds of Middle California were first described in 

 two publications by F. M. Anderson. 1 A fuller description with a 

 summary of previous geologic and palaeontologic work was given by 

 Ralph Arnold and Robert Anderson 2 in their report on the geology 

 and oil resources of the Coalinga District. 



1 Anderson, F. M., A stratigraphic study of the Mount Diablo range of Cali- 

 fornia, Proc. Calif. Acad. Sci., 3d ser., vol. 2, no. 1, 1905; A further study in the 

 Mount Diablo range of California, Proc. Calif. Acad. Sci., 4th ser., vol. 3, 1908. 



2 Arnold, Ealph, and Anderson, Eobert, Geology and oil resources of the 

 Coalinga District, Fresno and Kings counties, California, U. S. Geol. Surv. Bull. 

 398, 1910. 



