134 STUDIES, SCIENTIFIC AND SOCIAL chap. 



have preserved for us one of the most curious and instruc- 

 tive products of the great ice-age. This view of the origin 

 of the gorge is that adopted by Professor Bonney, who, in 

 his paper read before the Royal Geographical Society in 

 1893, says, " This chasm has been sawn by the sub-glacial 

 torrent, while the ice itself has moulded every rock on the 

 barrier into billowy undulations." I may, therefore, take 

 it for granted that this view is held by most geologists 

 who have attended to the subject, and it appears to me to 

 be the only reasonable one ; yet it is so important, and 

 leads to conclusions so entirely opposed to the views ex- 

 pressed by Professor Bonney in the same paper, that it 

 seems advisable to ascertain whether any collateral evidence 

 can be obtained in support of it. 



There are in Switzerland a number of other gorges 

 which have the same general characters, of being decidedly 

 water-worn throughout, very narrow and deep, and of 

 approximately the same width from bottom to top ; but 

 they are all formed by lateral streams where entering into 

 a main valley, not in course of the main valley itself 

 Such are the gorges of the Trient at its outlet to the 

 Rhone, that of Pfoefifers on the Rhine, and many others of 

 less importance on the tributaries of other Alpine rivers. 

 In many of the larger valleys almost every lateral tributary 

 enters the main stream either by a cascade or by a gorge 

 of this character, these gorges usually being the outlet of 

 the drainage of considerable valleys, the stream appearing 

 to have cut through a rocky barrier similar to that of the 

 Aar, but on a less impressive scale. Now all the gorges 

 which have these special characters have almost certainly 

 been formed in the same way — by sub-glacial torrents, 

 and, if so, the presence of such gorges would be an indica- 

 tion of geologically recent glaciation. It is true that simi- 

 lar gorges may have been sometimes formed, without the 

 intervention of an ice-covering, in rainless districts where 

 sub-aerial denudation would not eat away the upper lips 

 of the chasm, as it was being formed. This is to some 

 extent the case in the canons of the Colorado ; but although 

 the lower portions may exhibit the effects of water erosion 

 only, being by their great depth kept at a nearly uniform 



