1916] Martin: Pliocene of Middle and Northern California 221 



ports the occurrence of marine Pliocene which he correlated with 

 the Merced Series at Seven Mile Beach, but thought that they might 

 represent the lower portion, such as the beds at Capitola, there 

 being an abundance of Area trilineata Conrad. These beds were 

 resting upon a formation of volcanic ash, called by Osmont the 

 Sonoma Tuff. In some localities the tuff was associated with sand- 

 stones and conglomerates, and in other localities with lava flows. 

 Conformably beneath the Sonoma tuff occurred the Mark West 

 andesite. This series of formations, including the St. Helena rhyo- 

 lite which conformably overlies the Merced, rests unconformably 

 upon the Orindan Formation. The fauna obtained from the marine 

 sediments, in the neighborhood of Wilson's Ranch, seemed to war- 

 rant the correlation with the beds at Seven Mile Beach. The thick- 

 ness of the formation was in the neighborhood of two thousand feet. 



In 1906 Ralph Arnold published a monograph on the Tertiary 

 and Quaternary Pectens of California. 14 In this publication the 

 author gives a short review of each of the typical formations of the 

 Tertiary and Quaternary of California. He included a faunal list 

 for each formation and correlated them on that basis. The greater 

 portion of the Purisima Formation was placed unquestionably in 

 the Pliocene, although the lower portion was closely related to the 

 Miocene. The Merced Series was both Pliocene and Pleistocene, 

 the greater portion being placed in the upper Pliocene. Both the 

 Purisima and the Merced horizons were recognized in the Wildcat 

 Series in Humboldt County. 



The "Geologic Record of California," a paper published in 1910 

 by Dr. J. P. Smith, 15 contains a correlation table which includes 

 formations from the Archaean to the present. The Merced Series 

 is placed in the upper Pliocene and the Purisima Formation in the 

 lower Pliocene and uppermost Miocene. 



The geology of the Sargent Oil Field, Santa Clara County, Cali- 

 fornia, was worked out and published in 1911 by William F. Jones. 16 

 The formations concerned in the geology of this area include both 

 igneous and sedimentary from the Franciscan to the present. Only 

 the upper Miocene and the Pliocene are to be considered in this 

 paper. The Monterey shale is the most extensive and well developed 

 of the formations represented. Unconformably overlying the Mon- 



i* U. S. Geol. Surv. Professional Paper no. 47, 1906. 



is Journal of Geology, vol. 18, pp. 216-226, 1910. 



io Univ. Calif. Publ. Bull. Dept. Geol., vol. 6, pp. 55-78, 1911. 



