turf mofs, where the black colour of the waters difcovers the fource 

 whence they were ftained. 



Mr. Playfair fays," " Rivers have cut and formed, not the beds 

 " only, but the whole of the vallies through which they flow." (Page 

 353,) He told us before, " that all thefe channels have been cut by 

 " the waters themfelves, and that it is by the repeated touches of 

 " the fame inftrument, that this curious aflcmblage of lines has been 

 " deeply engraved on the furface of the globe." (Page 103) 



Yet M. St. Fond, when he found it neceflary to account for the 

 formation of a deep valley, I'efcarpment ou coule I' Ibie admits the in- 

 fufficiency of Mr. Playfair'^ inftrument; and fays, it was excavated 

 not by that paltry brook (cbeiif ruijfeau) but by fomc diluvian tor- 

 rent, (min. des volcans 173.) 



Dr. Huiion and Mr. Playfair feem to confider the inequalities on 

 the furface of the earth, to be produced by the operation of ri- 

 vers, as well as the excavation of vallies. 



I will treat of thefe two queftions feparately, beginning with our 

 mountainous inequalities ; and, fliould I be fo fortunate as to meet 

 Mr. Playfair's defponding geologift in his Alpine regions, calculating 

 how foon 



The great globe itfelf, 



" Yea, all which it inherit, fliall diffolve ; 

 " And, like this unfubftantial pageant faded, 

 " Leave not a rack behind." 



I would endeavour to difpel his fears by fiiewing him that, the ri- 

 vers, which he has been taught to think fo aftive in the deftruc- 

 tion of our globe, are very harmlefs, and that our inequalities have 

 been produced by other agents, which by all appearance, have long 

 ceafed to aft. 



I would requcft him to obferve, that in all mountainous trafts, 

 there is a ridge higher than the reft, from which the waters run 



down 



