50 



RESOURCES OF TENNESSEE. 



one underlaid, for the most part, by a massive sandstone, but here and 

 there the surface is formed of shales that are in places interbedded with 

 the sandstones. That portion of the surface, however, which lies east of the 

 Cincinnati Southern Railway is not properly a plateau, but is a complex 

 maze of sharp-topped ridges and deep-cut, narrow stream valleys, formed 

 on flat-lying shales and sandstones, by vigorous stream erosion. 



FIG. 3. Cumberland Plateau, in Cumberland County. 



The larger streams of most of the plateau are sharply cut beneath the 

 general surface and many of them flow in narrow gorges 300 to 500 feet 

 in depth, the valley walls in many places being made of precipitious cliffs 

 that may be in extreme cases 100 to 200 feet in height. This is particu- 

 larly true of the northern portion of the plateau west of the Cincinnati 

 Southern Railway in Pickett and Fentress counties, and is true in a some- 

 what less degree of many other parts of the plateau as well. Further, the 

 southern half of the plateau is deeply cleft longitudinally by a long, nar- 

 row, straight valley, occupied by the Sequatchie River. The middle por- 

 tion of the plateau in the vicinity of Crab Orchard, Crossville, and Mon- 

 terey, is less dissected by stream gorges than elsewhere. 



Barrier effect. The eastern margin known in the southern part as Wai- 

 den Ridge, and in the northern part as Cumberland Mountain, is itself a 

 steep- walled barrier that is broken by but few gaps that permit easy ac- 



