Petroleum or Rock. Oil 289 



supported by the geologic relations of the hydrocarbons, which 

 are found in large quantities only in rocks of sedimentary 

 character. Any organic substance which becomes enclosed 

 within the sediments may be a source of petroleum. There is 

 no evidence to show that any important oil field derived its 

 hydrocarbons from inorganic sources (F. W. Clarke) . 



Microscopic Animals and Plants 

 Possible Sources 



It is well to remember the enormous accumulation of 

 "oozes," the radiolarian and globigerina oozes, on the bottom 

 of the sea. The organic matter thus indicated is abundant 

 enough, if it decayed under proper conditions, to form more 

 hydrocarbons than the known deposits of petroleum now con- 

 tain. Animal matter in some cases, vegetable matter in others, 

 or both together, are supposed to be the source of supply. Some 

 oils are supposed to be of mixed origin, and it is thought by some 

 geologists that the mixed class is the most common. The idea 

 has also been held that Pennsylvania oils have been derived from 

 marine vegetation, while California oils were attributed to 

 animal remains. Wherever sediments are laid down enclosing 

 animal or vegetable matter there bitumens may be produced. 

 Sea weeds, mollusks, crustaceans, fishes, and microscopic organ- 

 isms may contribute material. In some cases plants may pre- 

 dominate; in others animals, and the character of the hydro- 

 carbons is likely to change accordingly just as petroleum varies 

 in different fields. Such differences are most easily explained 

 on the supposition that different materials have yielded the 

 different products. 



In California certain shale formations have been oil-pro- 

 ducing (notably the Monterey shale, of Tertiary age) . Dia- 

 tomaceous shales have been a source of oil to such an extent 

 that many geologists have come to regard the diatoms as the 

 organic source of the oil. It is not, however, fully proven. 

 Diatoms minute organisms so small that they cannot be dis- 



