72 THE MOUNTAIN. 



valleys between the mountains show somewhat diversified 

 surfaces. 



The mountain ranges west of the proper Alleghany are 

 not so regular and sharp in outline, and the valleys between 

 are of a different character. These ridges, as they are gen- 

 erally styled, are also called by different names in separate 

 portions of their extent, even when there is no interruption 

 of continuity of elevation. 



The whole group, with its characteristic scenery, its splen- 

 did system of foldings of the surface, or waves of mountain 

 and valley, upon minute exploration, is discovered to be in 

 strict conformity with the rock structure beneath. The to- 

 pography of a given portion of the earth's crust, with its 

 contour of outlines and surfaces, is necessitated by its geo- 

 logy, as absolutely as the form of an animal's body is fixed 

 by its skeleton, or stony foundation. 



The sharp regular mountains east of the Alleghany itself 

 are formed of different materials, and have a different char- 

 acter from the western collateral parallel ridges. The former 

 are made of the larger and more uniform members of the 

 geological series, those masses which preserve homogeneous 

 mineralogical composition through great extent of their thick- 

 ness, also sameness of mechanical constitution, or strength of 

 substance, over large geometric areas, and exhibit great uni- 

 formity in the style of fracture and plication of the strata. 



Those west of the Alleghany are more irregular and indefi- 

 nite in their outlines, from the more heterogeneous mineralo- 

 gical constitution and mechanical properties of the rocks of 

 that portion of the group of which they are formed. 



What is called especially the Alleghany Mountain (the 

 term Appalachian indicating the whole eastern oceanic sys- 

 tem) is the range of knobs, or irregularly serrated edge of the 

 summit-line of that vast plateau, or elevated range of table 

 lands, (much more correctly designated ranges of alpine 

 hills,) which forms the chain of water-sheds of the eastern 

 side of the continent. It is formed of a series of high out- 

 standing geological watch-towers, which coalesce in a crest- 



