406 C. SCHUCHERT PALEOGEOGRAPHY OF NORTH AMERICA 



Paleozoic continental seas, North America was certainly outlined, and 

 was then even larger than it is at present. This fact is also noted by 

 vValcott, 78 who states : 



"The continent was larger at the beginning of the Cambrian period than 

 during any epoch of Paleozoic time. . . . The continent was not then 

 new. ... It was approaching the baselevel of erosion over large portions 

 of its surface. ... I strongly suspect . . . that ridges and barriers of 

 the Algonkian continent rose above the sea . . . that are now buried be- 

 neath the waters of the Atlantic." 



A survey of the Paleozoic paleogeography here submitted shows that 

 the seas are of a continental character, for the marine waters of the four 

 quarters of the northern hemisphere flow in on the depressed inland 

 basins of the North American continent; further, that this vast land- 

 mass has in the main always been bordered by high lands. The sediments 

 of these seas are derived from the elevated areas of the continental mass 

 and there was no "contribution of rock material from outside or aid from 

 the ocean's waves or currents, either those of the Atlantic or Pacific. For 

 the most part, therefore, the growth of the continent . . . may be 

 said to have been endogenous. It began to be exogenous on the Atlantic 

 side in the Cretaceous era" (Dana). 



These facts and others stated on later pages prove that the North Amer- 

 ican continent in its entirety has always been essentially positive, and was 

 a greater land-mass just previous to the introduction of the Cambric and 

 the Siluric seas than it is now. Moreover, during the Paleozoic its sur- 

 face was variously buckled and elevated, but never very highly, owing to 

 the inwardly moving Atlantic, Gulf, and Pacific margins, thus giving rise 

 to shallow or continental island studded seas. During the early Mesozoic 

 the North American continent was again larger than it is at present, but 

 in late Mesozoic time, long after the Sierra Nevada deformation, another 

 great s}mcline was developed giving rise to a continental sea that did vast 

 endogenous work along the entire eastern side of the Eocky mountains 

 extending from the Gulf to the Arctic ocean. Finally, since the disap- 

 pearance of this, the Coloradoan sea, the North American continent has 

 had throughout almost its present size and the work of its marine waters 

 has been exogenous, due to overlaps of the oceans. 



As the North American continent now combines many positive ele- 

 ments that are particularly noticeable as separate elements during Paleo- 

 zoic times, when the mainland appears rather as a series of varying large 

 and small islands, it is thought advisable to give each component part a 



78 Walcott: Twelfth Ann. Rep. TJ. S. Geological Survey, 1891, p. 561 



