224 Evolution and Distribution of Fishes 



primary source of its supply. At times it is difficult to 

 determine whether the petroleum has originated in a fish- 

 bearing stratum and still remains there, or whether it has 

 not risen from such stratum, through porous ones overlying, 

 to become eventually sealed up in some porous sandstone or 

 sandy shale that covers the whole. Thus Adams (///: 38), 

 in treating of the eastern Texan region, records bituminous 

 clay-shale of Benton age. But from the Niobrara beds 

 above (that he calls Austin chalk) he separates off the 

 "Taylor Marls" that are largely made up of oil and gas 

 bearing sandstones. It seems not unlikely that the products 

 however came from Benton strata below. 



Prosser, Logan, and Williston {172) have given 

 detailed study to the corresponding Kansan beds. Here 

 also the Benton and Niobrara series are specially important. 

 Logan in describing the Benton series divides it into seven 

 minor systems, and in most of these abundant fish remains, 

 oysters, Inoceramus and other marine organisms occur 

 amongst bituminous strata. Some of the Kansan Benton- 

 Niobrara beds are very richly bituminous, and Williston 

 (p. 243) after taking note of the "abundant marine inverte- 

 brates" says: "The Niobrara deposits have been famous 

 for the past twenty-five years for the abundance, variety 

 and perfection of its vertebrate remains." Of fishes there 

 is an extraordinary abundance of their remains, while six 

 genera of Mosasaurus were frequent. In the upper beds, 

 that possibly correspond to the "Taylor marls," of Adams, 

 he further indicates that Turtles, abundant Plesiosaurs, 

 and toothed birds occurred, since the seas then had evident- 

 ly become shallower, while Logan and Williston alike em- 

 phasize squalodont and cestraciont elasmobranchs as being 

 profusely represented by their remains. The wealth and 

 variety of teleosts in the Kansan cretaceous rocks is well 

 set forth in Stewart's (op.cit. p. 386) and Loomis' (op. 

 cit pp. 213-282) lists. Stewart's comparative tables also of 

 American and Europeo-Asiatic genera (pp. 387-389) are 

 highly instructive. 



But in Canada the Cretaceous is likewise known to be as- 

 sociated with petroleum products. For, speaking of the 



