72 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



sand one hundred and ninety square miles. It is surrounded upon 

 all sides by a high, almost precipitous, wall or escarpment surrounded 

 by a broad flat top. The top, o)- broad plateau forming it, extends 

 from the base of the Cumberland Mountains, or rather Cumberland 

 Table land, on the east, to the shore of the old paheozoic Sea a few 

 miles beyond the Tennessee River on the Avest, and froui the State of 

 Alabama in the south, it extends across Tennessee and covers the 

 greater part of the soiithern and central portions of Kentucky. The 

 area of this extensive plateau within the State of Tennessee and im- 

 mediately surrounding the basin is computed by the State Commis- 

 sioner of Agriculture, in his Report for 1^87 (p. 15G), to be eight 

 thousand two hundred square miles. This wall and top with its 

 broad extent has been called by Professor Saffoi'd the " Highland 

 Rim," and the whole Basin and Highland Rim has been compared 

 by him to a great broad rimmed flat bottomed dish slightly tilted to 

 the northwest. This tilting to the northwest is due to a general dip- 

 ping of the whole country in that direction and is altogether indepen- 

 dent of any of the numerous directions of dip found locally. 



From this it will be seen that the Central Basin is simply an erosion 

 through the Highland Rim into the underlying formations. 



This Highland Rim is almost continuous in its circumscribing the 

 Basin. It is only broken Vjy four narrow rocky gorges through 

 which the Cumberland, Elk and Duck Rivei-s pass. At the north- 

 eastern corner the ('umlierlaud enters the basin through a long 

 narrow pass, and on the northwest again the same river passes out of 

 the basin by a gateway somewhat similai- to the one by which it 

 enters. Upon the south, the Elk River leaves the basin by a narrow 

 rugged channel, and upon the west another outlet of the same kind 

 aflords a pas.sage for the waters of che Duck River. Of these outlets 

 only those connected with the Cumberland River are navigable. 

 The others are too narrow, rocky and sliallow to be of any practical 

 use. 



Although these gorges are the only ones piercing the plateau of 

 the Highland Rim, and finding an outlet through it, the margin of 

 the Rim is broken into by numerous streams which have their sources 

 somewhere upon its broad flat top. These streams have cut for 

 themselves long narrow channels running back, sometimes several 



