During the Cretaceous Period 225 



Dakota sandstones of Alberta, Canada, Redwood (25: 

 125) says: "The Dakota sandstones at the base of the 

 Cretaceous series is saturated, over an area of at least 

 1,000 sq. miles, with inspissated petroleum, and is often 

 mentioned as the Tar Sand. It rests unconformably on 

 the Devonian limestones and shales, which are also petro- 

 liferous to a slight extent within the province, and abundant- 

 ly so both northwards in Mackenzie, and southward in 

 Ontario and the United States, so that the idea has found 

 favor in some minds that the Tar of the Dakota sandstone 

 is derivative from the Devonian series. But the latter, where 

 seen along the Athabaska and its tributary valleys, cut down 

 through the soft Cretaceous rocks, is devoid of any trace 

 of bitumen. It may be added that the Dakota beds are 

 petroliferous in other regions, where no such derivation is 

 conceivably possible." The above Canadian beds, in geolo- 

 gic position and petroleum yield, may correspond to the 

 Trinity beds of Eldridge and other authors. But the 

 writer would regard the Mowry shales, that lie toward the 

 base of the Benton series, as the more likely source of sup- 

 plies. This he has discussed in another work {173)- 



In face of the above evidence, the writer would consider 

 that with passage of numerous elasmobranchs, — perhaps 

 more importantly of ganoids, and of teleost descendants 

 from freshwater ganoids — into a marine environment, myri- 

 ads of these were at times destroyed by some sudden and 

 widespread cataclysmic action, were covered over within 

 at most a week to a few weeks, and in time gave rise to 

 marine supplies of fish oil, which in turn by destructive 

 analysis produced those petroleum supplies that man is now 

 utilizing. A like result is dealt with in next chapter for 

 Tertiary strata and Tertiary fishes. 



In a succeeding chapter detailed comparison will be 

 made of the genera and families of fishes that character- 

 ized respectively the freshwater and the marine strata of 

 Cretaceous age. But as furnishing a vivid picture of the 

 varied marine genera of teleosts, the writer subjoins a 

 table of these, prepared by A. Stewart (op.cit. 386) and 

 this also sets forth their stratigraphic relations. 



