OF THE APPALACHIAN CHAIN. 477 



presenting themselves in this position, they form narrow belts and 

 ridges among the older metamorphic strata towards the southeast. 

 Innumerable dykes and veins of all dimensions, and consist- 

 ing of a vast variety of igneous materials, penetrate this belt, 

 disturbing and altering its strata in a remarkable degi-ee. 



2. Immediately to the northwest of this mountain range is a 

 broad valley, which constitutes by itself a well-defined belt through- 

 out the entire length of the chain, displaying a remarkable constan- 

 cy in its structure and physical features. This, which we shall caU 

 the Great Appalachian Valleij, ranges from Vermont to Alabama, 

 under various local names, being known in New York as the 

 Valley of Lake Champlain and the Hudson river, in Pennsylva- 

 nia as the Kittatinny or Cumberland Valley, and further south 

 successively, as the Great Valley of Virginia and the Valley of 

 East Tennessee. Its average breadth throughout, is about fifteen 

 miles, forming an unbroken and nearly level plain, except in Vir- 

 ginia and eastern Tennessee, where several long insulated ridges, 

 rising in it, separate it for a greater or less distance into two or 

 more narrow parallel valleys. The stratification every where in 

 this great belt is exceedingly disturbed, the rocks consisting prin- 

 cipally of the three lower Appalachian formations, being, only in 

 a very few instances, invaded, however, by igneous dykes. 



3. Beyond the Great Appalachian Valleij on the northwest, is 

 a wide belt of long, narrow, parallel ridges and included valleys, 

 spreading northwestward to the foot of the great plateau of the 

 Allegheny and Cumberland mountains. This, which we propose 

 to call the Middle Mountain-beH, has a breadth varying from 

 thirty to sixty miles, its greatest expansion being in the curving 

 region of the Juniata in Pennsylvania. It embraces all the Ap- 

 palachian formations to the coal inclusive. 



4. The fourth or most northwestern of the belts into which we 

 have divided the Appalachian chain, commences with the south- 

 eastern escarpment of the gi-eat table-land of the Catskill, Alle- 

 gheny, and Cumberland mountains, and spreads northwestward 

 with a gentle declivity, as far as the limits of the last feeble axes 

 of elevation. The average breadth of this belt, measured from 

 the southeastern escarpment of the plateau, to the plain which 



