476 O.N THE PHYSICAL STRUCTURE 



gi-eat length, narrowness, and steepness ; the evenness of their 

 summits, and their remarkable parallelism. Many of them are 

 almost perfectly sti-aight for a distance of more than fifty miles ; 

 and this feature, combined with their steep slopes, and sharp, level 

 summits, gives them the appearance, seen in perspective, of so 

 many colossal entrenchments. Some gi-oups of them are curved, 

 but the outlines of all are marked by soft transitions, and an as- 

 tonishing degree of regularity. It is rather the number and gi-eat 

 length of the ridges, and the magnitude of the belt which they 

 constitute, than their individual gi-andeur or height, that places 

 this chain among the great mountain systems of the globe. From 

 the latitude of the Mohawk river, in New York, to the northern 

 boundary of Alabama, the chain in general consists of four par- 

 allel belts, the separate features of which it is convenient we 

 should define. 



1. The first or southeastern subdivision is the relatively naiTow, 

 undulating mountain range, which, in Vermont, is called the 

 Green Mountains, in New York the Highlands, in Pennsylvania 

 the South Mountain, in Virginia the Blue Ridge, and in North 

 Carolina and Tennessee the Smoky or Unaka mountains. This 

 is rather a zone of closely united ridges, than one gi-cat mountain 

 axis, though the latter is somewhat its character in Virginia, 

 North Carolina, and Tennessee, in which States it has its greatest 

 breadth and elevation. The average width of this belt may be 

 stated at about fifteen miles, and its height, which is more varia- 

 ble than that of any other portion of the general chain, undulates 

 betAveen about one thousand and five thousand feet above the 

 sea. 



The rocks of this tract consist for the most part of the older 

 metamorphic strata, including gneiss, and micaceous, chloritic, 

 talcose, and argillaceous schists, together with masses referable to 

 the earliest Appalachian formations, sometimes in a highly altered 

 condition. Throughout nearly the whole distance, from Ten- 

 nessee to the Susquehanna, these latter rocks occupy the north- 

 western slope of the main ridge, and form the ranges of hills, 

 sometimes of gi-eat height, flanking it on the northwest ; while in 

 Pennsylvania, New Jersey, Massachusetts, and Vermont, besides 



