J 98 On the Causes which have operated 



practical fjicts in the general question. And, notwith- 

 slandinff all Mr. Fafey's denial, tor he has vel offered no- 

 thi|*g in the way of argument, it is a general truth diffused 

 over the whole surface of the globe, that excavated vallevs 

 and their streams do coincide in their direction with the 

 natural fall of the country, and do intersect ai angles also 

 corresponding with that fall, and at corresjiondinir levels ; 

 and while this vast unison of effects absolutely denion>tra(es 

 the action of the streams as its natural cause, it is utterly 

 and altogether inexplicable by any other natural process or 

 operation. 



Elence it is, that Mr. Farcy has never yet ventured to 

 hint at what he deems the natural cause of the excavation 

 of vales; and with a larger poition of that confidence v\hich 

 he condemns, and which, without havini;; truth on its side, 

 would, indeed, be the extreme of absurdity, I venture to 

 pronounce his entire ineapacilv to afford any probal)le solu- 

 tion of those extensive general truths — -the elevated situa- 

 tion of the spring-heads — the common direction of the 

 vales and streams with the fall o!^ the country — and their 

 uniform intersections and levels. He commuted himself 

 in the first instance by denying the action of the streams, 

 and in doing so he has completely shut himself out from 

 the question, and is now utterly unable to advance a single 

 Step towards its elucidution. 



Hithertu Mr. Farey has only tried toextincuish the lights 

 held up, and endeavoured to thrirw the general question 

 into uller darkness, by balancing petty and puny excep- 

 tions against a more extensive chain of general and har- 

 monizing facts than are to be met with in any other portion 

 of geology ; and it is this spirit of altercation working only 

 to conceal and obscure, instead of entering with fair views 

 into the just merits of the general case, that has constrained 

 nie to speak so stronirly as I have done. I was, and am 

 still, disposed to think very highly of Mr. Farey, as an 

 exceedingly acute, intelligent, and industrious observer; 

 but every thing he has yet said on the subject of valleys 

 proves how justly I appreciated his talents as an ii^vestigator 

 of natural ':ause?. 



The only obscurity, I am well convinced, which hangs 

 over the natural excavation of valleys, arises from not duly 

 estimating the mechanical action of water when rapidly 

 descending a declivity over the ordinary materials of our 

 earth. There is not, perhaps, a mountain on the globe, 

 which a stream of water will not cut in two, allowing it 

 only a sufficient fall, and a sufficiency of time: two cir- 

 cumstances 



