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POPULAR SCIENCE MONTHLY. 



through the region is not likely to recognize the valley form, as most 

 of the roads are in smaller valleys between the ridges, but once gain 

 some commanding elevation and the great valley is seen stretching away, 

 its ridges and hills melting into insignificance on its apparently level 

 bottom. The decomposed rock makes a fertile soil which early attracted 

 settlers. From New York to Alabama it is the abode of a prosperous 

 people with well tilled farms and comfortable homes. 



Extending westward from the valley is a plateau region which 

 merges on the north and west into the Mississippi valley and is known 



Belief Map of the Chattanooga District. (Photographed from model by E. E. Howell.) 



as the Cumberland Plateau. The geologist finds no difficulty in 

 accounting for the transition from valley to plateau when the rock 

 arrangement is seen. Here instead of the highly tilted strata of the 

 valley, the rock layers are nearly horizontal. Instead of the troughs 

 and ridges of the valley, the surface, while rough, has an even sky line 

 which tells of a former approximately level surface. The elevations are 

 steep and the streams seem to have no regular arrangement — in short, 

 this region is a 'dissected' plateau. The surface stratum of rock in 

 general is a sandstone which is underlaid by a stratum of more easily 

 soluble limestone. When a stream has cut through the sandstone layer 

 and reaches the limestone, it deepens its valley more rapidly than before 

 and consequently flows in a steep trench. 



The overlying sandstone protects the limestone beneath and prevents 



