451 



down on both fides, and generally at right angles; that this ridge, 

 (very properly ftiled by Livy the divortia aquaruni) has been fixed 

 upon as the boundary of empires, of diftri£ls, and of properties ; that 

 though out of the reach of rivers, this ridge often exhibits greater 

 inequalities than the contiguous trafts ; fometimes confifting of a fuc- 

 ceflion of round, diftinft mountains ; at others, of a long dorfum, 

 occafionaliy cut down in gaps, (hewing the mountain ftrata at the 

 fame level on both fides. 



I could fliow him, that thefe gaps, (through which the roads 

 croffing the mountains generally run) could never have been cut out 

 by a river, unlefs we concede to Dr. Hutton his curious pofition (the- 

 ory, page 296) " nor is there upon the continent, a fpot at which 

 " fome river has not run ;" his friend, Mr. Playfair, foftens the ex- 

 prefllon a little, faying, may have run (353). If rivers have run once 

 through fuch gaps, their courfe muft have been up one fide of the moun- 

 tain, and down the other. 



I would remind our geologift, that the long chains of mountains 

 bounding the valley of the Nile on both fides, feem to have vallies 

 and defiles exaftly like our own ; yet, in that country they have 

 neither rain nor rivers. That hilly countries are alpine regions in mi- 

 niature ; their inequalities generally fimilar, though upon a fmaller 

 fcale ; yet fuch vallies are common without even a brook. 



Rivers have been fo much dwelt upon, by Dr. Hutton and Mr. 

 Playfair, as the great agents and inftruments employed in carrying 

 away the materials of our world, that I mull trefpafs a little farther 

 on the reader's patience, for which I hope to be excufed, the rather 

 as it is a fubjeft with which I ought to be well acquainted ; my paf- 

 fion for angling having led me to explore the courfes of moft rivers 

 I ever refided near ; all of which nearly refemble each other, their 

 differences arifing merely from their different degrees of declivity. 



(3 L 2) Beginning 



