160 C. SCHUCHERT THE XORTH AMERICAN GEOSYXCLIXES 



of a nuclear area, lout in Permian time its western half became rugged 

 or mountainous, with a geosynclinal sea over the eastern portion. It 

 therefore appears to be a nucleus that has undergone a second cycle of 

 crustal deformation. Llanoria, on the other hand, even though but a 

 northeastern extension of Mexico during much of the Paleozoic, yet has 

 its own history, apparently becoming actively mobile and mountainous 

 for the first time late in the Mississippian. Finally, Arctic America is 

 bordered by Pearya, part of which is now risen into the United States 

 mountains. These borderlands are plotted on the map, figure 3, and the 

 more important ones will now be described in more detail. 



APPAL AC HI A 



As long ago as 1856^^ Dana defined Appalachia as ^"the region toward 

 the Atlantic border, afterward raised into the Appalachians,'" but the 

 actual name for the borderland was not given until 189 T, and then by 

 AVilliams.^^ In the present connection, we will restrict the term Appa- 

 lachia to the southern half of the eastern borderland lying to the north 

 and west of Antillia ; the northeastern borderland has long been known 

 as Acadia, of which Xovascotica is the outer portion (see page 162). 



The western margin of Apj)alachia extends from about the highlands 

 of New York southwestward into central Alabama, where this old land is 

 overlapped along its inner side and southern end by Mesozoic and Ceno- 

 zoic deposits. Across its eastern side the Atlantic Ocean began to spread 

 for the first time in the C'retaceous, and it continued to do so periodically 

 during the Cenozoic. How far this borderland fomierly extended into 

 the Atlantic Ocean may never be learned, even approximately, but en the 

 basis of the very thick Devonian elastics of the Appalachian geosyncline 

 extending from central Virginia to the Catskills, BarrelP^ estimated tliat 

 their volume is at least 63,000 cubic 'miles, or considerably more than the 

 volume of the Sierra ]S"evada of California. On this estimate of sediment 

 that was clearly derived from a highland to the east and southeast, and 

 on the assumption that this land had the height of the present Sierra 

 Xevada, Barrell concluded that the watershed of Appalachia in Devonian 

 time was where the 100-fathom line of the Atlantic is now, in other 

 words, roughly 100 miles east of Xew Jersey. Therefore, if the eastward 

 slope of the watershed was like the western one, AjDpalachia extended out 

 into the ocean at least 200 miles beyond the present shoreline of the At- 



" Dana : On American geological histor.v. Amer. Jour. Sci. (2). vol. 22. p. .319. 



" H. S. Williams: On the southern Devonian formations. Amer. Jour. Sci. (4), vol.3, 

 p. 394. 



1' Joseph Barrell : Upper Devonian delta of the Appalachian geo.syncline. Amer. Jour. 

 Sci. (41, vol. 37, pp. 248-249. 



