158 C. SCHUCHERT THE XORTH AMERICAN GEOSYXCLIXES 



by every one, at least tacitly, that this geosyncline has always been a part 

 of the [N'orth American continent. In other words, the Appalachian geo- 

 syncline has never been a part of the oceans or mediterraneans, nor does 

 it, like the mediterraneans, lie between continents (see page 194). Fur- 

 thermore, as the loading of this geosyncline did not make it subside, it 

 follows that there must have been another crustal element orogenetically 

 connected with it. This was, of course, the outer, mobile, progressively 

 rising borderland, Appalachia, which finally became a highly elevated 

 anticlinorium, delimiting the Appalachian geosyncline on the west and 

 shedding into it most of its sediments. The Appalachian-Allegheny 

 Mountains are, therefore, a combined synclinorium and anticlinorium, 

 or, as Dana would say, a "polygenetic mass." 



BORDERLAXDS OF NOETH AMERICA 



(See Map, Figure 3) 



GEXERAL DlSCrSSIOX 



From the geographic position of the geosynclines near the margins of 

 the continent, and the further fact that the main masses of their sedi- 

 ments came not from the medial area of the continent, but from more or 

 less narrow lands facing the oceans, it is clear that Xorth America was 

 originally much more extensive than now. Since these facts are already 

 true in Lower Cambrian time, it is also clear that the extent of greater 

 Xorth America was established in Proterozoic time. Even throughout 

 the later Proterozoic we see the presence of a Cordilleran geosyncline in 

 the same general area as the seaways of the early Paleozoic, and it follows 

 that greater Xorth America came into existence at least in early Pro- 

 terozoic time. The present area of Xorth America is over 8,300,000 

 square miles and Greenland has in addition about 850,000 square miles. 

 In Proterozoic time, on the other hand, the writer believes that greater 

 Xorth America had an area, of over 11,000,000 square miles; that since 

 then Greenland has become a separate land, and that in addition some 

 2,000,000 square miles of the continent have been warped and fractured 

 into the oceanic realms. These statements are portrayed on the maj), 

 figure 2. 



Almost the entire outer areas of Xorth America show in their geologic 

 structure that a more or less wide belt has been the most mobile part of 

 the continent. At various times these marginal lands have periodically 

 risen into more or less high lands, and they have been the main source 

 for the sediments of the geosynclines situated along their inner sides. 

 On the outside of the borderlands lie the permanent oceanic basins. How 



