A, Guyot on the Appalachian Mountain System. 167 
zone shows that they are but the last undulations due to the ac- — 
tion of the same forces which have upheaved an 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 corrugations properly so-called. is is a large central val- 
ley 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; 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 contracts in breadth towards the south, in Virginia, but 
reaches its greatest dimensions in Tennessee where it measures 
rom 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 extends without any great interrup- 
tion from Vermont to Alabama. In Vermont it bears the name 
form throughout 
Although thes 
at the cent: 
its 
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