THE CENTRAL BASIN OF TENNESSEE. 71 



witliin, are also neai'ly 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 countiy, and thus by the slow process of 

 washing and weathering, the i-ocks 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 regular manner. The size of the central opening is too small to 

 admit extraordinary floods, nor is it possible with the level margin 

 around to suj)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 jH'obable that 

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

 the same time ru[)tured and cracked the beds in certain lines ; that 

 afterwards the rains wei-e swallowed into openings on these fractures 

 producing by denudation the basins of the sink-hole country and 

 further enlarging the original fractnres by flowing through them and 

 thus forming a vast system of caverns which surround the western 

 ■coalfleld. — Owe7i, Geol. Survey of Kentucky, Vol. IV, p. 511. 1S61). 



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

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

 Dutton, 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 probably not 

 U})on so large a scale nor so greatly i-amified. 



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 ti-aversed 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 northwesterly and southeasterly direction is from fifty to fifty- 

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

 width. The area of this great basin has been computed at six thou- 



