Petroleum or Rock Oil 293 



shale, and much the greater part of the oil in these fields occurs 

 in that formation or in other formations in contact with or 

 near to that formation. 



On the east side of the Coast Ranges the formations have 

 different characteristics and consequently different formations 

 are regarded as the source of the oil. On the east side of the 

 ranges in the San Joaquin Valley the Monterey formation is 

 absent in some fields, but other formations carry diatoms or 

 foraminifera, and in each case the oil is found only in these or 

 closely associated formations. There is no doubt that the 

 petroleum in the Santa Maria district is indigenous to the 

 Monterey shale. Bitumen is a characteristic part of that for- 

 mation throughout its wide extent over an area covering hun- 

 dreds of square miles. On the west side of the Coast Ranges 

 the Monterey shale is the principal formation containing dia- 

 tomaceous and foraminiferal material, and is the source of most 

 of the oil. On the east side the Monterey is the source of oil 

 only when it is diatomaceous. But other formations partake 

 of this characteristic, and when they do are regarded as sources 

 of some of the oil. In the Coalinga district the oil is believed to 

 be derived from organic shales of the Upper Chico formation 

 (Upper Cretaceous) and upper Tejon (Eocene, Tertiary) . It 

 is believed that the oil originated from organic matter, both 

 animal and vegetable, once contained in these beds. The shales 

 consist of tests of foraminifers and diatoms and some others in 

 such abundance as to warrant assumption that the animal and 

 vegetable material that must have been contained in them was 

 adequate to furnish the hydrocarbons more than equivalent to 

 the quantity of petroleum found in this field. 



Oil from Minute Organisms in 

 Monterey Shale 



The conclusion is unavoidable that some ingredients of the 

 Monterey shale gave rise to the oil. Diatoms were the chief 

 source, although animals and perhaps other plants also con- 



