THE CENTRAL BASIN OF TENNESSEE. 67 



soutli-east. Such in simplest terms is the geological structure, and 

 there is no doubt but that the coal basins of the Warrior and Cahaba 

 were once continuous ; that at the time of the disturbances along the 

 Appalachians, they together with the underlying formations down at 

 least to the Quebec or Knox Dolomite were uplifted into a long 

 anticlinal fold ; that this fold was fractured along its axis or summit, 

 thus affording a channel for denuding waters, and finally that the 

 gi'eat mass of sandstones, coal Vjeds, shales, and limestones, which 

 constituted the fold has been broken down and removed by the action 

 of running waters till nothing is left of it now except the low rim 

 on each side adjacent to the coal measures." This valley is from six 

 to eight miles from coal tield to coal tield. 



These two valleys exhibit in many ways peculiarities similar to 

 what are found in the district in Central Tennessee and Southern 

 Kentucky and, as we shall see further on, may be looked upon as the 

 resultants of similar causes. 



In some cases valleys of elevation have been denominated as anti- 

 clinal valleys owing to the peculiarity of their formations. It might 

 be better to give them that name as their existence is due to the 

 presence of the anticlinal, while the valley has nothing to do with the 

 elevation of the ridge. 



If. Valleys of Erosion or Denudation. — A valley of erosion is one-- 

 due to the eroding and denuding effect of water in some of its many 

 forms, or to atmospheric or some other sub-aerial causes. It is. 

 asseited that erosion never was the primaiy cause of the production 

 of a valley, but rather that denudation is only a secondary cause- 

 operating fron) some pre existing condition of things, and thereby- 

 forming a valley of denudation. 



A very insignificant agency may be the cause of the formation of an: 

 immense gorge, with its narrow channel, precipitous inaccessible sides, 

 and with its rushing turbulent torrent, or the beginning of a broad 

 fertile valley, whose smiling fields, watered by a slowly flowing and 

 meandering stream, extend over an area of many miles, to be sur- 

 rounded on its margin by I'ounded hills gradually rising to the level 

 out of which the valley had been formed. 



The land emei-ging from the sea may have risen furrowed with 

 ripple markings, small and scarcely perceptible, such as we often see. 



