THE CENTRAL BASIN OF TENNESSEE. 71 



■within, are also nearly horizontal. Near the centre there is an 

 •opening of from three to fifteen feet in diameter. Into this opening 

 the water which has fallen within the margin of the basin has been 

 drained since the day when the rocks exposed within were raised 

 above the drainage of the country, and thus by the slow process of 

 washing and weathering, the rocks which once filled these cavities 

 have been worn and carried down into the subterranean drainage of 

 the country. All this has evidently come to pass in the most quiet 

 and i-egular manner. The size of the central opening is too small to 

 admit extraordinary floods, nor is it jiossible with the level mai-gin 

 around to sui)pose that these cavities were worn by eddies in a cur- 

 rent that swept the whole cavernous member of the subcarboniferous 

 limestone of Western Kentucky, but the opinion is probable that 

 the upheaving force which raised these beds to their present level, at 

 the same time ruptured and cracked the beds in certain lines ; that 

 afterwards the rains were swallowed into openings on these fractures 

 pi'oducing by denudation the basins of the sink-hole country and 

 further enlarofino; the original fractures bv flowinof through them and 

 thus forming a vast system of caverns which surround the western 

 coalfield. — Otven, Geol. Survey of Kentucky, Vol. IV, p. 511. 1S6I). 



This class of basins is not confined to the district included in 

 Kentucky and Tennessee. Similar sink-hole basins were noticed by 

 Datton, in the Grand Caiion District, and which he says imply a 

 system of subterranean rivulets, but it is not more wonderful than 

 the endless caverns in Kentucky and Indiana, and it is pi'obably not 

 •upon so large a scale nor so greatly ramified. 



The great central Basin of Tennessee is a valley of erosion, due 

 according to all existing evidences to simple aerial causes. This 

 valley is of a somewhat irregularly formed oval shape having a broken 

 into and fringed margin. Its long axis extending in a northeastern 

 and southwestern direction is about one hundred and twenty miles in 

 length — that is excluding the narrow gorge traversed by the Cumber- 

 land River at the northern end, and the Elk river valley at the 

 ■southern extremity. The shorter axis or width of the basin measured 

 in a noitliwesterly and southeastex-ly direction is from fifty to fifty- 

 five miles, measured in the latitude of Nashville it is sixty miles in 

 •width. The area of this gi'eat basin has been computed at six thou- 



