Appalachian Geosyncline. 253 



changes which each successive age has wrought. The record 

 has been interpreted in terms of the great Tertiary mountain 

 systems of Eurasia, consisting of their overthrust structures, 

 piedmont slopes, waste-tilled basins, and delta plains, — as the 

 members of a greater system, each part bearing relations to the 

 other. The fragmentary remains of late Paleozoic Appalachia 

 and its waste which still exist, when pieced together in accord- 

 ance with this pattern, rise to equal grandeur. An orogenic 

 era began in Appalachia in the Devonian and spread as time 

 went on. Great as was the Upper Devonian mountain building, 

 it was limited and was only premonitory of the greater, wider 

 movements of the Pennsylvanian. During the Upper Devonian 

 the interior waters facing the southern Appalachians received 

 only meager supplies of sediment. The crust was there at rest. 

 But with the coming of Pennsylvanian times the mountain 

 system lengthened to the southwestward and its curving arc 

 finally embraced as far as Texas the interior continental basin 

 into which it poured its waste. The Permian witnessed only 

 the final collapse of the interior geosynclines and the inward 

 march of the conquering mountains. The Appalachian revolu- 

 tion began in reality in the Middle Devonian, the first 

 mountain bulwarks being thrown up on the far eastern side 

 of the Appalachian system and to the north. There in Maine, 

 New Brunswick, and Nova Scotia granitic intrusions and 

 volcanic outpourings of Devonian age took place and in the 

 nearby basins the waste resulting from uplift was laid down. 

 The southern part of that system supplied the debris which 

 filled the geosyncline in Pennsylvania. 



Our knowledge of the Appalachians as a distinct mountain 

 system begins with the opening of the Cambrian. The basal 

 formations of the Cambrian, or late pre-Cambrian, thousands 

 of feet in thickness, are geosynclinal deposits whose volume 

 testifies to the destruction of great mountains to the east. 

 Lesser movements took place at intervals and one of consider- 

 able magnitude at the close* of the Ordovician. These, how- 

 ever, were relatively brief and minor orogenic manifestations. 

 They were separated and obliterated by periods of prolonged 

 quiet and erosion. They were more comparable in character 

 to the movements of the Mesozoic and Cenozoic and do not 

 rise to the prolonged growth and culmination of those greater 

 revolutions which preceded and closed the Paleozoic Era. 

 The latter, because of its completer record, has become known 

 as The Appalachian Revolution and its earlier development in 

 the Upper Devonian has been traced in this paper. 



The Devonian mountains are gone, and where once they rose 

 in defiant height their very foundations are broken and buried, 

 but in remnants of formations born of destruction we may 

 read the epitaph which records their greatness. 



Yale University, Dec. 2, 1918. 



