254 Evolution and Distribution of Fishes 



rock that splits into layers (igo). Everything indi- 

 cates that here we have again to deal with a combination 

 of physico-biological factors connected with volcanic activ- 

 ity, volcanic dust-showers, wide-spread death of animals, and 

 rapid entombment of them in the hardening volcanic dust, 

 such as we have frequently emphasized already. 



In view of such conditions it is not surprising that some 

 of the Oligocene-Miocene strata are becoming increasingly 

 celebrated in the commercial world as sources of bituminous 

 supplies. But as in the case of Eocene and Cretaceous oil 

 beds already treated of, the richest oil reservoirs are con- 

 nected with marine rocks. Thus the Monterey coastal beds 

 of California consist largely of shales that may vary from 

 2000 to 4000 feet in thickness, and which yield abundant 

 supplies of oil. According to Eldridge rich masses of fora- 

 minifera, borings of Pholas, and fish scales are the most 

 prominent features, while in some beds enormous quantities 

 of diatoms occur. So it has been suggested by some writers 

 that the petroleum is derived from the soft substance of 

 the foraminifers and diatoms. But no proof exists that 

 such organisms can produce even approximately sufficient 

 fixed oils, and therefrom yield by analysis bituminous prod- 

 ucts, that would account for even a tithe of the oils now 

 being abundantly set free. The universal occurrence of 

 fish remains gives, we believe, the key to the situation. 



The enormous deposits that were laid down along the 

 Eocene to Pliocene coastal areas of California are outlined 

 by Eldridge in some of his conclusions (op. cit. p. 321). 

 Thus "there are at least 10 or 12 horizons in the 20,000 

 feet or more of strata from Eocene to Pliocene that carry 

 oil in quantities of economic value. The reservoirs are 

 either conglomerates, sandstones, or the arenaceous mem- 

 bers of the great shale groups in the Miocene. The strati- 

 graphical and structural conditions under which oil occurs 

 in the known fields, are many times repeated elsewhere in 

 the Coast Range and the territory contiguous. In several 

 instances faults, or intense disturbances of the strata, have 

 accompanied the folding of the entire system, causing along 

 their lines, interstitial spaces in which petroleum could 



