510 C. SCHUCHERT PALEOGEOGRAPHY OF NORTH AMERICA 



besides producing new fractures and faults. Such displacements have 

 taken place especially in the region of mountain plateaus, where the 

 pressure was least." Such settling also adds its quota to the transgres- 

 sions, but in all probability the total effect is small. 



Oceanic participation in the transgressions. — Having examined into the 

 causes of the various transgressions and emergences, the degree to which 

 the different oceans have contributed to these results will now be set forth. 

 The synopsis of the writer's paleogeography is tabulated in the columns 

 "Seas present" and "Direction of flow of water — in or out." 



It is seen that the Atlantic ocean has not made a very decided record 

 from the standpoint of deposits and faunas. The Saint Lawrence sea has 

 been the chief area of its extension, and while this sea and the straits 

 across New Jersey have often sent their biota into the Mississippian sea, 

 yet the northern Atlantic or Poseidon has had the least faunal control 

 of all the oceans. Its waters often entered the Appalachian sea, but only 

 three times did they dominate this basin, these occurrences taking place 

 in the Clinton, the Salina, and the Lower Devonic intervals. From the 

 physical side, however, the ocean has had a marked influence throughout 

 the Paleozoic in elevating bordering lands and mountain chains, thus pre- 

 venting the faunas of interior seas from mixing much with those of the 

 Atlantic. In other words, the North Atlantic did not dominate the conti- 

 nental Paleozoic seas of North xAmerica, and during the Mesozoic it was 

 practically non-existent. 



During the early Paleozoic the Arctic ocean had a great influence. In 

 the Middle and Upper Ordovicic and Siluric the waters of the Hudson sea 

 dominated the continental seas, and through the Cordilleran sea had a 

 marked effect in the Middle Cambric, the late Devonic, and early Missis- 

 sippic. In the late Triassic, and again in the Middle Comanchic, the 

 Arctic ocean overlapped the greater part of Alaska, while in the Cretacic 

 it connected with the Gulf by way of the Coloradoan sea. At other times 

 this ocean had no appreciable influence. 



The Gulf of Mexico, as the southwestern part of Poseidon, has had the 

 most continuous existence of all the great bodies of water, being present 

 throughout most of the Paleozoic, Mesozoic, and Cenozoic eras. Its 

 waters, however, have been confined to the eastern half of the United 

 States. The only times when entrance of the Gulf was blocked were the 

 Cambric, Salina, Chemung, late Permic, the greater portion of the Trias- 

 sic, and most of the Jurassic. It was dominant throughout the Ordovicic, 

 Clinton, Onondaga, most of the Mississippic, Pennsylvanic, Permic, late 

 Jurassic, Comanchic, Cretacic, and Oligocene. Its influence, therefore, 

 was most marked in the late Paleozoic and late Mesozoic. 



