162 GEOLOGY. 



period merely, but the close of an era as well. While these changes 

 are commonly said to have taken place at the close of the Cretaceous, 

 it is probably more accurate to say that they began late in the Upper 

 Cretaceous, and continued into the succeeding period. The close of 

 the Cretaceous may be said to have been the time when these changes 

 first made themselves felt profoundly. They consisted of deformative 

 movements, a part of which were orogenic, and of igneous eruptions 

 on an unprecedented scale. 



General movements. — In the closing stages of the period, the sea 

 which had lapped over the Coastal plain of the Atlantic and Gulf was 

 withdrawn toward the abysmal basin. Data now in hand point to 

 the emergence of the eastern Gulf region in advance of the Atlantic 

 coast, while the emergence of the Texan area was probably still later, 

 and this implies that the changes were not due wholly to variations 

 of the sea, but in part at least to differential warpings of the coastal 

 belt. The Appalachian mountains, which had their first period of 

 folding during the Permian, and which had been reduced to a pene- 

 plain by the beginning of the Cretaceous, were bowed upward at some 

 later time, and this second period of growth seems to fall within the gen- 

 eral period of deformation here under consideration . This later move- 

 ment was chiefly vertical, while the Permian deformation was primarily 

 horizontal. 



In the western interior, the prolonged period of crustal oscillation 

 which marked the Laramie, marked also the beginning of the end 

 of the Cretaceous. By the close of the Laramie, the sea had with- 

 drawn from the extensive area occupied by the Great plains, and 

 from large areas in the mountains west of the plains. It is probable, 

 indeed, that most of the Cordilleran region was elevated bodily at 

 this time, though not to its present height. Great areas which had 

 been submerged were however brought above the critical level, and 

 the movements were, therefore, recorded. Records of similar move- 

 ment in some other regions where they probably took place are want- 

 ing, or the record is less clear; but it is probable that the eastern 

 interior underwent changes of level, relative to the sea, at this time. 

 Enough is known to make it clear that a large part of the continent 

 was affected by the general withdrawal of the. sea. 



Orogenic movements. — The development of mountains by folding 

 was probably in progress in the last stages of the Cretaceous period, 



