THE COMANCHEAN PERIOD. 123 



still others, the latter system is absent. 1 The Knoxville formation of 

 the Coast Range of California contains some igneous rock. 2 



The faunas of the Shastan and Comanchean systems are markedly 

 unlike, and since the differences do not seem referable to climate, it 

 seems necessary to suppose that there was some sort of a barrier 

 between the two regions. In the United States, this barrier seems 

 to have been a wide one, but in Mexico it was probably narrow, 

 for the Comanchean fauna, or some part of it, extends west to the 

 western part of Mexico (Sonora), while farther south the Pacific fauna 

 reached eastern Mexico (San Luis Potosi). The exact position of 

 the barrier which separated the oceans is not known. It appears 

 to have lain farther west in northern Mexico, and farther east in 

 southern. The failure of the two faunas to mingle does not prove 

 the complete separation of the oceans, but it indicates that any con- 

 nection there may have been was slight, or that the barrier between 

 them extended well to the south, perhaps as far as Central America. 



Though the exact time relations of the Comanchean and Shastan 

 series have not been determined, they are believed to be approximately 

 equivalent. It follows that the exact relations of the Shastan system 

 to the Tuscaloosa and Potomac series are not defined. 



North of the United States. — Farther north, the Lower Cretaceous 

 beds (Queen Charlotte series) occur in the Queen Charlotte Islands, 3 

 where they have a thickness of between 9000 and 10,000 feet. In 

 British Columbia, the coast fine was east of the Coast Ranges, and 

 extended farther and farther east with increasing latitude, until the 

 ocean swept clean across the site of the Cordilleras in the early part 

 of the period, and extended south along the area which -is now 

 the east base of the mountains. 4 In this southerly extension of the 

 sea, the area of deposition was separated from the Pacific by land 

 occupying the site of the Selkirks. The Kootenay formation is per- 

 haps partly contemporaneous with these marine beds, but largely 

 younger. The Comanchean system of British Columbia generally rests 



1 Roseburg, Ore., folio, U. S. Geol. Surv. 



2 Fairbanks, San Luis folio, U. S. Geol. Surv. 



3 Dawson, Geo. M., on the Earlier Cretaceous Rocks of the Northwestern Por- 

 tion of the Dominion of Canada, Am. Jour. Sci., Vol. 38, 1889, pp. 120-127. This 

 article contains a map showing relations of land and water on the northern Pacific 

 coast in the early Cretaceous. 



4 Dawson, Science, March 15, 1901; and Bull. Geol. Soc. Am., Vol. XII, p. 87. 



