54 Professor Guyot on the Physical Geography 



Although these features are common to the Appalachian system 

 throughout its entire length, nevertheless it may be divided from north 

 to south into three divisions which present very remarkable differences 

 of structure. Passing the eye over the physical chart which accom- 

 panies this article we at once distinguish in the longitudinal extent of 

 the Appalachian system two principal curvatures, the one at the north 

 from Gasp6 to New York, the concavity of which is turned towards the 

 southeast ; the other at the centre, from the Hudson to New River in 

 Virginia, with its concavity also towards the southeast ; the third from 

 New River to the southwest extremity of the system, the direction oj 

 which is nearly straight or forming a gentle curve concave towards the 

 northwest. These three divisions, diminishing in extent, from the north 

 to the south, are well marked ; at the north, by the deep valleys of the 

 Mohawk and the Hudson, which break through the Appalachian system 

 to its base and across its entire breadth ; at the south, by the New River 

 whose deep valley with vertical walls also separates regions whose 

 orographic characters present remarkable diflferences. 



The northern division is much the most isolated ; it is geologically the 

 most ancient, since its upheavals appear coeval with the Silurian and 

 Devonian epochs, and are thus much anterior to the rest of the system, 

 which only emerged after the deposit of the carboniferous rocks which it 

 has elevated. Four hundred feet more of water would separate all the 

 vast territory of the northern division from the American continent. One 

 hundred and forty feet would convert into an island all New England 

 and the British possessions as far as Gaspe ; for the bottom of the valley 

 occupied by Lake Champlain and the Hudson does not in any part ex- 

 ceed this level. 



I distinguish in this northern portion three physical regions ; 1st, the 

 triangular plateau of the Adirondack, with its mountain chains more or 

 less parallel, between Lake Champlain and the St. Lawrence, Lake 

 Ontario and the Mohawk : 2nd, New England, with the two swells of 

 land separated by the deep valley of the Connecticut, and forming the 

 base of the Green and White Mountains : 3rd, the northern region, with 

 the prolongation, towards the northeast, of the same features of relief 

 from the source of the Connecticut through Maine into Canada and New 

 Brunswick to the promontory of Gaspe and the Bay of Chaleurs. 



The middle or central division extends in length about 450 miles. The 

 eastern region, or region of folded chains, at first very narrow about 

 New York, presents towards the centre, in Pennsylvania, its greatest 

 breadth which again diminishes towards the south. It is composed of 

 a considerable number of chains much curved towards the west, and 

 remarkable'for their regularity, their parallelism, their abrupt acclivities, 

 the almost complete uniformity of their summits, and their moderate 

 elevation, both relative and absolute, which varies from 800 and 1500 

 to 2500 feet. The chains, however, increase in elevation towards 

 the south, while they become more numerous and more indented. In 

 the Peaks of Otter, in Virginia, they attain to 4000 feet. 



The western region, or the region of plateaus, is quite narrow in the 



