OF THE EARTH'S SURFACE. 181 



In whatever manner we account for the production of these 

 forms, it is certain, that they present themselves on the sur- 

 face of water-worn rocks. I have also observed them upon 

 the surface of a mass of snow which had been acted upon, and 

 partly removed by a strong wind. As the abrasion occasioned 

 by a fluid in motion seems alone to possess that power, we 

 may reasonably conclude, then, that a fluid has acted where 

 such forms occur. 



Now, it is a fact of which I shall presently lay various ex- 

 amples before this assembly, that the very rocks over which, 

 according to the theory advanced in this paper, torrents of wa- 

 ter have flowed, loaded with sand, and gravel, and large stones, 

 and accompanied with streams of mud, are found to exhibit at 

 their surface all the characters of abrasion lately mentioned ; 

 — the rotundity and flowing character ; — the excavation of hol- 

 lows into the form of waving grooves ; — the concave scoopings, 

 and the obtuse-angled, and waving ridges. Circumstances, 

 then, seem to justify the conclusion, that, in fact, mighty tor- 

 rents have traversed these districts. 



In addition to the facts mentioned, and in company with 

 them, another set also occur in these scenes, which powerfully 

 corroborate the same conclusion. As stones of considerable 

 bulk are often carried down by torrents, it is reasonable to ex- 

 pect, that upon rocks along which they have been hurried, 

 and on which they could not fail to act as grinders, traces 

 should shew themselves of that passage by scratches and 

 abrasions of various sorts ; and I have little doubt, that such 

 will be found, when the effects of great floods in rapid rivers 

 are properly examined ; especially where a stream of mud has 

 accompanied the torrent. Not having had occasion, however, 

 to visit any scene of this sort, since the importance of the ob- 

 servation occurred to me, I have as yet, only met in rivers 



with 



