CHAPTER XIV. 

 THE COMANCHE AN (LOWER CRETACEOUS) PERIOD. 1 



Introductory. 



At the close of the Jurassic period, large areas in the western part 

 of North America which had been submerged became land, and at 

 the beginning of the succeeding period, the larger part of the North 

 American continent was above sea-level. The history of the Cretaceous 

 period, as that term has commonly been used, is rather complex. 

 The general sequence of events in North America is somewhat as fol- 

 lows: (1) Early in the period there was a somewhat widespread warp- 

 ing of the continental surface, resulting in sedimentation at many 

 points within the continental borders. Submergence was extensive 

 in Mexico and Texas, and the sea extended thence as far north as the 

 Ouachita Mountains, and temporarily beyond, while on the Pacific 

 coast a narrow border of the present land was beneath the sea. Along 

 the Atlantic and Gulf coasts, and in some parts of the western interior, 

 considerable tracts were brought so low, or into such an attitude, 

 as to become the sites of deposition, though not submerged beneath 

 the sea. A prolonged period of sedimentation followed these geo- 

 graphic changes. (2) This period of sedimentation was followed by 

 an interval when most of the areas which had recently been the sites 

 of deposition, whether marine or non-marine, were exposed to subaerial 

 degradation. (3) After this interval had been sufficiently long to 

 allow of very considerable erosion of the Early Cretaceous beds, the 

 sea encroached upon the Atlantic and Gulf borders, covering, and in 

 general spreading beyond, the non-marine formations of the earlier 

 stage. It again covered Texas, and presently extended northward 

 over the Great Plains to the Arctic Ocean, forming a great 



1 For a full review of the American Cretaceous, up to 1891, see White (C. A.) Bull. 

 82, U. S. Geol. Surv. 



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