56 RESOURCES OF TENNESSEE. 



iron ores are abundant. Much of the timber of the region has been cut 

 and the tendency is, as everywhere, toward its further destruction. This 

 section is capable of supporting a very much larger population than it 

 now has, under conditions that will vary from medium to good, and there 

 is no inherent reason why it should not as a whole become quite a pros- 

 perous section of the State. 



CENTRAL PLAIN. 



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Origin. This division of the State forms a basin that has been pro- 

 duced by the erosion and unroofing of the gentle dome mentioned in the 

 description of the Highland Plain. It is 50 to 60 miles in width and about 

 100 miles in length, with its longer axis extending somewhat northeast 

 and southwest. Murfreesboro is a few miles southeast of the center of 

 the basin and Nashville is situated near its northwestern margin. The 

 general surface of the plain is some 300 to 400 feet below that of the 

 surrounding Highland Plain. 



Drainage. Cumberland River flows into the basin or plain from the 

 northeast, and after receiving numerous tributaries within the basin leaves 

 it by a relatively narrow groove cut in the northwestern part of the sur- 

 rounding Highland Plain. Harpeth River rises in the Central Basin and 

 flows northwestward out of the basin in a similar valley cut in the High- 

 land Plain. Duck and Elk rivers drain the southern part of the basin 

 and likewise cut through the encircling highland. It is evident that all of 

 these streams were in existence before the basin was formed and that they 

 cut their way downward through the rocks of the encircling rim as the 

 central dome was unroofed by erosion and the basin slowly developed. In 

 no other way can one explain why rivers flow from a lower land across a 

 higher one. It is well known to geologists that the Central Basin was 

 never a lake as some have supposed, and the streams that leave.it could 

 never have been outlets by which the supposed lake was drained. It would 

 have been exceedingly improbable that a lake would ever have four out- 

 lets and much more improbable that each would have cut down at so 

 even a rate as to have all survived the draining of the lake. 



Surface. The general surface of the Central Plain is a gently rolling 

 one produced by stream erosion and solution on limestones, whose doming 

 is so gentle that they are almost flat-lying. The soils of the region are 

 the insoluble residue left by the solution of the limestone. Where this 

 solution has been more rapid the soils form a thick surface mantle, but 

 where the limestones are more chertv and hence less soluble, the soils are 



