RESUME OF STRUCTURAL GEOLOGY OF NORTH AMERICA 



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and drifted apart from the continent at the south end to form the Gulf 

 of Raja California which is floored by oceanic crust. Deep but local 

 basins sank in southern California. 



The Colorado Plateau block was uplifted with associated subsidence 

 on the south and west. Several laccolithic groups were intruded into the 

 Plateau strata, and several volcanic piles accumulated around the southern 

 and eastern margins. In central Wyoming certain blocks were depressed 

 along normal faults, particularly the Laramide Sweetwater Range. The 

 Great Plains came into existence by uplift progressively greater toward the 

 west. The Laramide Rockies were also uplifted, starting a new erosion 

 cycle. 



The marginal areas of the Gulf Coastal Plain continued to subside 



greatly under a heavy load of deltaic sediments. An area in northwestern 



Florida became emergent. The Atlantic Coastal Plain south of Ixmg 

 Island gradually rose and the sea retreated, but north of Long Island 

 submergence and overlap of the sea occurred. The submergence has 

 also been effective in Quaternary time southward where emergence 



has occurred previously. 



Broad arching in the Appalachian region continued. 



The Canadian Shield had been depressed under the weight of the 

 ice sheets but in post-glacial time has lifted progressively to the north. 

 The tilting starts at the hinge line shown on Plate 15 and amounts to 

 700 feet along the northern shores of Lake Superior, and possibly 900 

 feet along the eastern side of James Bay at the south end of Hudson Bay. 



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