120 STUDIES, SCIENTIFIC AND SOCIAL chap. 



atmosphere being shut out by the superincumbent ice 

 and all variation of temperature avoided, the torrent cut 

 for itself a very narrow groove, sometimes with overhang- 

 ing sides, as it found layers of somewhat softer rock to 

 eat away; and the upper surface of the rock being 

 ground smooth by the ice, the atmosphere has had 

 little effect since, and the gorge, while deepened below, 

 has remained as restricted above as when first eroded. 

 Such are the gorges of the Trient, Leuk, Pfaflfers, and 

 many others well known to Alpine tourists. I am not 

 aware whether such extremely narrow winding gorges, 

 often only two or three feet between the rock walls, are to 

 be found in countries which have never been glaciated. I 

 do not myself remember reading of any, though of course 

 tremendously deep ravines are common, but these are of 

 quite a different character. Should it be found that 

 these extremely narrow rock-walled gorges are peculiar to 

 glaciated districts they will afford us a means of estimating 

 the amount of glacial erosion in valleys where no lake 

 basins have been formed.^ 



The Lake of Geneva as a Test of the Rival Theories. — When 

 I recently began to study this question anew, I was inclined 

 to think that the largest and deepest of the Alpine lakes, 

 such as Geneva, Constance, Lago Maggiore, and Lago di 

 Garda, might perhaps have originated from a combination 

 of earth-movements with ice-erosion. But on further 

 consideration it appears that all the characteristic features 

 of erosion are present in these as fully as in the smaller 

 lakes. They are situated in the largest river-valleys or in 

 positions of greatest concentration of the glacier-stream ; 

 their contours and outlines are those of eroded basins ; 

 while all the difficulties in the way of an origin by earth- 

 movements are as prominent in their case as in that of any 

 other of the lakes. I will therefore discuss, first, some of 

 the chief objections to the erosion theory as applied to the 

 above named lake, and then consider the only alternative 

 theory that has obtained the acceptance of modern writers. 



One of the first objections made was, that the lake did 

 not lie in the direction of the greatest action of the glacier, 



1 Some evidence on this point will be found in the next chapter. 



