SUMMARY OF MESOZOIC HISTORY 277 



Texan and western interior areas were marked by the deposition 

 of the largely continental (Dakota) sandstone early in the period. 

 At the same time the western edge of the continent was submerged 

 under the sea. 



In later Upper Cretaceous time, the Atlantic Coast and eastern 

 Gulf districts continued much as in the earlier Upper Cretaceous. 

 The western Gulf and western interior districts, however, were 

 marked by a vast transgression of the sea from the Gulf to the 

 Arctic, while the Pacific border continued as earlier in the Upper 

 Cretaceous. Map Fig. 151 shows the condition of the continent in 

 this later Cretaceous time. 



Mountain Making. — The Jurassic period was closed in the 

 west by the " Sierra Nevada Revolution," when strata of great 

 thickness were folded into mountains along the present site of the 

 Sierras and probably also the Cascades. There was also some 

 deformation in the region of the Coast Ranges. 



The Mesozoic era was closed by one of the most profound 

 physical disturbances in the post-Algonkian history of North 

 America, if not in the world, — the " Rocky Mountain Revolu- 

 tion," — when strata were more or less deformed by folding and 

 faulting throughout much of the Rocky Mountain system. At 

 the same time the whole eastern side of the United States, includ- 

 ing the Appalachians, which had been worn down to a peneplain, 

 was distinctly upraised without renewed folding of the rocks. 



Vulcanism. — While the later Triassic (Newark) sandstones 

 were forming on the Atlantic Coast, there were considerable in- 

 trusions and extrusions of igneous rocks, now represented by such 

 masses as the Palisades of the Hudson and the Holyoke Range of 

 Massachusetts. 



Accompanying the Rocky Mountain Revolution there were 

 tremendous outpourings of lava in the northwestern portion of 

 the United States. 



Climate 



The character and distribution of organic remains, both plant 

 and animal, pretty clearly prove the climate of the Mesozoic to 

 have been mild to possibly even warm temperate, with an appre- 

 ciable distinction of climatic zones, though not at all comparable 

 to those of the present. Warm temperate plants of the Cretaceous 

 are found even within the Arctic circle. 



