of the ApyalackiaJi Mountain System, 55 



southern part, but acquires towards the north the greatest breadht 

 which it attains in any part of the Appalachian system. Its highest 

 terraces occupy all the State of New York south of the Mohawk, and a 

 considerable part of Pennsylvania and culminate in the plateaus in the 

 neighborhood of Lake Erie, where the mean altitude of the plateau 

 reaches 2000 feet, the ralleys preserving a height of 1500 feet, while 

 the hills reach 2600 feet. 



This table land forms a remarkable water-shed from which the waters 

 descend by the Susquehanna into the valley of the Chesapeake and the 

 Atlantic Ocean, by the Genesee and St. Lawrence to the same ocean, 

 and by the Alleghany and Ohio to the Gulf of Mexico. The Susque- 

 hanna thus starts from Lake Erie at the extreme western border of the 

 plateau, and runs across all the Appalachian system and its mountain- 

 ranges to its eastern base. More to the southward the eastern escarp- 

 ment of the plateau divides, as far as the sources ofthe Potomac, the waters 

 of the Atlantic coast from those of the Gulf of Mexico. It is the same 

 escarpment which bears the local name of Alleghany Mountain, a name 

 which continues to be applied, south of the waters of the Potomac, to 

 the dividing ridge along the sources of the various branches of James 

 River, and even to the irregular hills which form a water-shed between the 

 waters of the Upper Roanoke and New River, across the Great Valley, 

 near Christiansburg. Through all this middle region the name of Blue 

 Ridge is applied to the main eastern chain which separates the Great 

 Valley from the Atlantic slope, and which is cut by all the rivers which 

 flow out of it. 



The southern division, from New River to the extremity of the system, 

 is much the most remarkable for the diversity of its physical structure 

 and its general altitude. Even the base upon which the mountains 

 repose is considerably elevated. Although the elevation of the Atlantic 

 plain at the eastern base of the mountains is only 100 to 300 feet in 

 Pennsylvania, and 500 in Virginia near James River, it is 1000 to 1200 

 feet in the region ofthe sources ofthe Catawba. In the interior of the 

 mountain region the deepest valleys retain an altitude of 2000 to 2 TOO 

 feet. 



From the dividing line in the neighborhood of Christiansburg and 

 the great bend of New River the orographic and hydrographic relations 

 undergo a considerable modification. The direction of the principal 

 parts ofthe system is also somewhat changed. The main chain which 

 borders the Great Valley on the east, and which more to the north, under 

 the name of the Blue Ridge, separates it from the Atlantic plain, gradually 

 deviates towards the southwest. A new chain detached on the east, 

 and curving a little more to the south, takes now the name of Blue 

 Ridge. It is this lofty chain, the altitude of which, in its more elevated 

 groups, attains gradually to 5000 and 5900 feet, which divides in its 

 turn the waters running to the Atlantic from those of the Mississippi. 

 The line of separation of the eastern and western water, which, to this 

 point, follows either the central chain of the Alleghanies, or the western 

 border of the table-land region, passes now suddenly to the eastern chain 



