"64 PROCEKDINGS OF THE CANADIAN INSTITUTE. 



THE CENTRAL BASIN OF TENNESSEE. 

 A Study of Erosion by William Kennedy. 



Valleys and their Formation. 



How are valleys formed ? Have they no rules guiding their 

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

 position or even their existence merely matters of chance and 

 governed by no tixed laws ? 



In their structure and formation there are laws as fixed as those to 

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

 understood when they are rightly interpreted. 



Valleys are depressions in the surface of the plane of the globe in 

 much the same manner as mountains are prominences or elevations 

 upon the same plane. Valley and mountain are com[)lementai'y of 

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

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

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

 miles in every dii-ection and in fact completely enclosing the valley. 

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

 rules govei'ning its construction are sometimes a little diflerent from 

 those affecting the formation of a valley. 



Valleys have been formed and are now in course of construction 

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

 have received their present forms and recent ones have started out to 

 form themselves would yji'obably be to enumerate nearly every known 

 valley in the world. They ma}', 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 obviously 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 gieat 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 valley have ceased to exist. 



