CHAPTER XXII 



Conditions at the beginning of the period. The opening 

 of the Comanchean period found the continent of North 

 America very largely out of water, the long gulf from the 

 northwest having been excluded at the close of the preceding 

 period. On the west coast the series of rugged mountains 

 which had been produced by the Sierran disturbance were 

 being eroded, and the material supplied by their decay was 

 spread along the shores of the Pacific Ocean. The present 

 Rocky Mountains and most of the numerous ranges of the 

 Great Basin region were not then in existence. From the 

 Pacific mountains to the Atlantic Ocean there were probably 

 no prominent highlands, except some low mountains in the 

 Carolina region and perhaps others in New England. By 

 this time the folded ranges of the Appalachian system had 

 been worn down to a lowland or peneplain, over which sluggish 

 rivers meandered on their way to the Atlantic Ocean and the 

 Gulf of Mexico, and above which a few scattered hills rose as 

 monadnocks. 



The beginning of the coastal plain. Up to this time the 

 coast line of eastern and southern United States appears to 

 have been considerably farther out toward the edge of the 

 continental shelf than now, for almost no Paleozoic or early 

 Mesozoic rocks of marine origin have been discovered there. 

 In the Comanchean, for the first time, sediments were laid 

 down over a considerable part of the old Appalachian land, 

 now represented by the Piedmont Plateau. In the broad, 

 level flats and marshes back from the coast, deposits of sand 

 and clay with occasional carbonaceous layers were formed. 



1 Often called the Lower Cretaceous period. 

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