526 THE COMANCHEAN PERIOD 



age. It is overlain unconformably in some places, and without 

 apparent unconformity in others, by the (Upper) Cretaceous (Chico 

 series). 



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 latitude, until the ocean swept clean 

 across the site of the Cordillera 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 contem- 

 poraneous 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, where it contains coal. It occurs 

 also on the west coast of Greenland, where the beds are thought to 

 represent some such horizon as that of the Kootenay, or Potomac. 



Close of the Period 



Considerable changes in the geography of North America brought 

 the Comanchean period to a close. Along the Atlantic and Gulf 

 borders considerable tracts were converted from areas of depo- 

 sition into areas of erosion. The system was somewhat deformed 

 and faulted in both Texas and Mexico. In the southern Coast 

 Range of California there was folding of the Lower Cretaceous beds, 

 accompanied by volcanic activity, while in other places the sea 

 spread itself over areas which had been land. Still other areas in 

 the west appear to have emerged at this time, and never to have been 

 submerged since. 



On the whole, the deformative movements at the close of the 

 period were more extensive, so far as present knowledge goes, than 

 those which occurred in the midst of any one of the Paleozoic 

 periods as here denned. On stratigraphic grounds, therefore, the 

 distinctness of the two systems is clear. The case is hardly less 

 clear on the paleontological side. 



1 Dawson, Geo. M., Am. Jour. Sci., Vol. XXXVIIL 1889, pp. 120-127. 



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



