•64 PROCEKDINGS OF THE CA.VADIAX IN'STITUTE. 



THE CENTRAL BASIN OF TENNESSEE. 

 A Study of Erosion by William Kennedy. 



Valleys and their Formation. 



How are valleys fonned ? Have they no rules guiding their 

 structure 1 or are their architectuie, their form, their outlines and 

 position or even theii- existence merely matters of chance and 

 governed by no fixed laws 1 



In their structure and formation there are laws as fixed as tho.se to 

 be found in any other division of geology and as clear and readily 

 understood when they are rightly interpreted. 



Valleys ai'e depressions in the surface of the ])lane of the globe in 

 much the same manner as mountains are prominences or elevations 

 upon the same plane. Valley and mountain are comi)lementary of 

 each other, so to sj)eak of the one implies the presence of the otlier. 

 Only, that in some cases the mountain pai-t of the two is of a par- 

 ticularly flat broad type; the flat top extending over a gieat many 

 miles in every direction and in fact comj>letely enclosing the valley. 

 Then, however, the enclosed depression is called a Basin and the 

 rules governing its construction are sometimes a little diflerent from 

 those affecting the foi'mation of a valley. 



Valleys have i^een formed and are now in course of construction 

 in various ways. To enumerate all the modes in which old valleys 

 have received their pi-esent forms and recent ones have started out to 

 form themselves would proV)ably be to enumerate nearly every known 

 valley in the world. They may, however, be classified into various 

 divisions according to the primary causes of their lormation. For 

 the purposes of such classification all valleys may be divided into 

 four different kinds, each being due to the peculiar manner of the 

 inception of the valley. This is oliviously the proper manner in 

 which such classification should be made as no valley exists, or at 

 least none is known to exist, in which a great part of the size and 

 form of such a valley cannot be traced to erosion or denudation. 

 The effects of erosion are recognizable in numerous cases long after 

 the traces of the original cause of the \alley have ceased to exist. 



