of the A'p'palacJdan Mountain System. 53 



seldom varied by any peaks or crags. In the extreme northern and 

 southern portions, however, this character is considerably modified. 

 There the system loses very much of its uniformity and its physical 

 structure becomes far more complicated ; the form of simple parallel 

 ridges almost entirely disappears. 



There is one feature of the Appalachian system which distinguishes it 

 from the ranges of the Jura ; it is the well marked division into two 

 longitudinal zones of elevation, one turned towards the shores of the 

 Atlantic, in which the form of parallel chains just spoken of predomi- 

 nates, and the other turned towards the interior, which is composed of 

 elevated and continuous plateaus, descending from the summit of their 

 eastern escarpment, in the centre of the system, in gentle stages towards 

 the basins of the lakes and the valley of the Ohio. Occasionally minor 

 chains, very little elevated from their base, wrinkle the surface of the 

 table-lands. Their parallelism with those of the eastern mountainous 

 zone shows that they are but the last undulations due to the action of 

 the same forces which have upheaved and folded that region, and which 

 have raised at the same time, the mass of these more uniform plateaus. 

 Thus when from any point we traverse the Appalachian system from 

 the Atlantic, we encounter first a plain more and more undulated and 

 gradually ascending to the foot of the mountains ; then a mountainous 

 zone with its ranges parallel and its valleys longitudinal ; at length a 

 third zone of uniform plateaus slightly inclined towards the northwest, 

 and cut with deep transverse valleys. 



Another feature not less conspicuous characterizes the region of cor- 

 rugations properly so-called. This is a large central valley which 

 passes through the entire system from north to south, forming, as it were, 

 a negative axis through its entire length. This is what Mr. Rogers calls 

 the Great Appalachian valley. At the north it is occupied by lake 

 Champlain and the Hudson river ;• in Pennsylvania it bears the name of 

 Kittatinny or Cumberland valley. In Virginia it is the Great valley j 

 more to the south it is called the valley of East Tennessee. At the 

 northeast and at the centre its average breadth is fifteen miles ; it con- 

 tracts in breadth towards the south, in "Virginia, but reaches its 

 greatest dimensions in Tennessee where it measures from fifty to sixty 

 miles in breadth. The chain, more or less compound, which borders 

 this great valley towards the southeast is the more continuous and ex- 

 tends without any great interruption from Vermont to Alabama. In 

 Vermont it bears the name of Green Mountains, which it retains to the 

 borders of New York ; in the latter State it becomes the Highlands ; in 

 Pennsylvania, the South Mountains; In Virginia the Blue Ridge; in 

 North Carolina and Tennessee the Iron, Smoky, and Unaka Mountains. 

 On the northwest of the great valley between the latter and the borders 

 of the plateau parallel there extends a middle zone of chains separated 

 by narrow valleys, the more continuous of which is the range which 

 bounds the central valley. This zone has a variable breadth in different 

 parts of the system, and the number of chains which compose it is by 

 no means uniform throughout. 



