THE MOUNTAIN. 71 



height, their most considerable altitude being 6470 feet above 

 the sea level. This is the height of Mount Mitchell, in North 

 Carolina, which is also said by some geographers to be the 

 "highest mountain summit east of the Mississippi River." 

 Some of these mountain ranges, as the Blue Ridge, are also 

 composed of the old metamorphic strata, gneiss, and altered 

 slates, and sandstones, embracing even the formations char- 

 acterized by the presence of fossils, or organic forms ; while 

 the principal part of the belt of the Appalachian chain is 

 composed exclusively of the sedimentary paleozoic division 

 low in the geological series. And thus from geological mu- 

 tation, and consequent topographic change, it comes that 

 different members of the chain, in the same lines of continuity 

 of elevation, are called by different names in the course of 

 their range through the United States. 



Their height is from two thousand five hundred to six 

 thousand feet, with an approximate average of three thousand 

 feet, above the level of the sea. They form a range of hydro- 

 graphic axes, which separate the waters that flow into the 

 great interior valley of North America and Gulf of Mexico 

 from those which flow over the Atlantic plain into that ocean : 

 as the Rocky Mountains, on the west, separate those majestic 

 streams which flow to the east and south through the trough 

 of the Mississippi River, from the west or Pacific water-shed. 



In their middle and southwestern range, this group of 

 mountains, with its large, rich, and fertile intervening valleys, 

 in its transit through the States, presents a series of chains, 

 or lines of elevation, with great regularity of crests and ac- 

 clivities, and more or less uniformity of geographic features. 



That portion of the Appalachian group, the individual 

 ranges of which are called by different names, east of the 

 Alleghany proper, exhibits a series of sharp, symmetrical 

 mountains, presenting long lines of parallelism, with crests 

 as regularly defined in outline as the ridges of a well-plowed 

 field, separated by valleys as regular as furrows in the same. 



Their crest-lines display regular and beautiful horizons, 

 which are almost mathematical lines for miles; while the 



