74 



PROCEEDINGS OF THE CANADIAN INSTITUTE. 



The average elevation of the Highland Rim taken from the mean 

 levels for Railroad purposes gives on the 



feet. R. R. Survey. 



Eastern and south-eastern sides. . . . 1019 Mean of 13 Stations. 



Northern side S 1 6 " " 3 



Western and South-western sides . . 951 " " 6 " 



-or an average elevation of 942 for the whole Rim. The mean average 

 elevation of the floor of the Basin above the same point and from the 

 same authorities taken from twenty-nine stations is 567 feet. These 

 measurements are above the level of mean tide in Mobile Bay. It 

 will thus be seen that the average amount of erosion necessary to 

 form this Basin would be a thickness of 375 feet extending over an 

 area of 6190 .square miles, and this after the surface of the country 

 had reached the level of the summit of the escarpment. Nor was 

 this the whole of the erosion that has evidently taken place in this 

 region of the world as there are many circumstances pointing to the 

 belief that denudation has removed an extent of sub-carboniferous and 

 carboniferous rocks if not greater, at least as extensive as the whole 

 -of the Tennessee Coal field as at present existing. 



The abruptness with which the escai-pment rises from the level of 

 the bottom of the Basin will be seen from the following figures taken 

 from the alignments of the various Railroads crossing it. 



LoCALITV. 



2f ear EdgetieldJunction . 



" Gallatin 



" TuUahoma 



■On Tennessee and Ala- 

 bama Railroad 



l^ear Pulaski 



Tfashville, Chattanooga 

 and St. Louis R. R. . . 



Authority. 



Survey. 

 L. N. R. R. 



R. R. Survey. 

 C. S. R. R. 



E. R. Survey. 



