THE MOUNTAIN. 73 



line, irregular, undulating and zigzag, and when approached 

 closely from the east, give the appearance of a chain of sepa- 

 rate, short mountains, and knobs almost isolated, towering 

 above the region at their bases ; but approached from a greater 

 distance, or from the west, present horizons of straight lines 

 or gentle undulations. The depressions between these knobs 

 are called gaps of the mountain. They are of every shape 

 and form, from simple flexures in the general line of trend, 

 scooped out depressions, or notches cut into the side of the 

 mountain mass, to short, abruptly terminating, or irregular, 

 tortuous and divided valleys, the bottoms of which are the 

 conduits, or rocky beds of the streams which flow southeast 

 from the steep escarpment of the mountain. These gaps or 

 gorges are sometimes cut into the mountain several miles, 

 and even clear through the entire mountain mass, as in the 

 gaps of some of the considerable creeks and rivers. They 

 penetrate the coal-bearing rocks, giving to the eastern margin 

 of the great bituminous coal-field a notched or irregular rim, 

 as points of the coal-seams with accompanying rocks stretch 

 out toward the knobs, forming the sinuous and jagged edge 

 of the great basin. 



The knobs, or swells of the mountain themselves, are stra- 

 tified piles of rocks left between the deep cuts or gorges of 

 denudation made into the side of the elevated mass of broken 

 heights called the Alleghany Mountains. The mineral masses 

 forming the summits of the high buttresses or outstanding 

 peaks of the mountain are constituted of the large group of 

 silicious rocks at the base of the coal series, including the 

 conglomerate, or its representative in coarse sandstone layers, 

 forming the floor of the coal measures. 



The gaps referred to between these peaks are simply deep 

 cuts, or sinuosities gouged by the denuding forces out of the 

 groups of rocks which make the mountain, and which are 

 here found with gentle dips, in some places approaching 

 nearly to the horizontal position. 



Westward of this range of knobs and gaps, and between 



7 



