734 GEOLOGY 



The fauna of the Shastan group is markedly unlike that of the 

 Comanchean of Texas, and since the differences do not seem refer- 

 able to climate, it seems most rational to suppose a barrier to 

 marine life between the two regions. In the United States, this 

 barrier was perhaps wide; but in Mexico it was probably narrow, 

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

 western part of Mexico, while farther south the Pacific fauna 

 reached eastern Mexico. The exact position of the barrier which 

 separated the oceans is not known. It is possible, on the other 

 hand, to think of ocean currents of different temperatures, as 

 determining the differences of faunas. Though the exact time 

 relations of the Comanchean and Shastan series have not been 

 determined, they are believed to be approximately equivalent. 



North of the United States. Farther north, Lower Cretaceous 

 beds (Queen Charlotte series) occur in the Queen Charlotte Islands, 1 

 where they have an estimated thickness of between 9,000 and 10,000 

 feet. In British Columbia, the coast line was east of the Coast 

 ranges, and extended farther and farther east with increasing lati- 

 tude, 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. 2 The Kootenay 

 formation is perhaps partly contemporaneous with these marine 

 beds. The Comanchean system of British Columbia generally rests 

 unconformably on the Triassic system, and contains some volcanic 

 material and, locally, coal. 



Farther north, the Lower Cretaceous has not always been sepa- 

 rated from the Upper, but the former has extensive development in 

 some parts of northern Alaska, 3 where it contains coal. It is also 

 believed to occur on the west coast of Greenland, where the beds 

 are believed to represent some such horizon as that of the Koote- 

 nay, or Potomac. 4 



1 Dawson, Geo. M., Am. Jour. Sci., Vol. XXXVIII, 1889, pp. 120-1J7. 



2 Dawson, Science, March 15, 1901; and Bull. Geol. Soc. Am., Vol. XII, 

 p. 87. 



3 Professional Papers 15 and 20, U. S. Geol. Surv. 



4 White and Schuchert, Cretaceous Series of the West Coast of Greenluu<l, 

 Bull. Geol. Soc. Am., Vol. IX, pp. 34:3-308, 1898. 



