During the Cretaceous Period 223 



The Cretaceous however, like the other formations 

 already studied, is often characterized by bituminous 

 material around fish remains, and in some parts of the 

 world by rich reservoirs of gas, oil, bitumen or asphalt. 

 Probably the richest bituminous centres are in central and 

 north-central North America. The deposits however of 

 this material have a new significance and importance in our 

 present study. For while we would consider that all of 

 the supplies from older formations — the Silurian, Old Red, 

 Carboniferous, Permian and Triassic, probably also largely 

 the Jurassic — were derived from analyzed fatty oils of 

 freshwater fishes, it seems now to be as clearly and largely 

 derived from marine fishes of Cretaceous age. Thus Fenne- 

 man in describing the Cretaceous oil-field of Boulder, Colo. 

 (770:322) says: "practically the entire mesozoic group 

 is represented in this district, and most of it is of interest 

 in the study of the oil." Again Eldridge, Prosser, Logan, 

 Williston and Adams amongst other investigators have 

 examined the oil fields of Kansas, Oklahoma, N. E. Texas 

 and Arkansas.* 



Reference to the table of correlation on p. 211 will 

 show that over the above region the Potomac formation 

 forms the base of the system, and that above it are the 

 Knoxville, Kootenay, and Horsetown. Together these 

 form the Comanchean system and have a varying thickness 

 of 2000 to 6000 feet. They are made up of beds in part 

 of freshwater, in part of marine origin. The basal part 

 of the Potomac is the Trinity group of beds, rich in fish 

 and invertebrate marine fossils. These beds also contain 

 rich bituminous supplies. 



But the Upper Cretaceous is specially noteworthy. For 

 the Benton and Niobrara series are both of marine origin; 

 the former at least is extremely rich in bituminous products; 

 and the strata, in particular the lower beds known as the 

 Mowry shales, are in places crowded with fish-remains of 

 marine habitat. Often the fishes are surrounded by oily 

 products, as if the latter were still in contact with the 



The writer treats in detail regarding the above question in his volume, "Fishes the 

 Source of Petroleum," (1923). 



