138 STUDIES, SCIENTIFIC AND SOCIAL chap. 



in the cutting of the great gorge by the sub-glacial 

 torrent, the Kirchet itself must have been greatly lowered, 

 and was probably, when the ice first reached it, at least 

 150 feet higher than its present highest bosses, or about 

 800 feet above the present level of the upper plain. 

 What is the depth of the alluvial deposit in this plain we 

 do not know, but as it extends more than two miles up 

 the valley, with a rise of about 30 feet in a mile, it is 

 probably not less than 200 feet deep. But if we go back 

 to the pre-glacial period before the gorge was cut, the 

 valley-bottom must have sloped upward from the level of 

 the Kirchet, and must therefore have been about 800 feet 

 higher than it is now. It follows, that while the gorge 

 was being cut, the floor of the valley above it was being 

 ice-ground, resulting in a basin about 1,000 feet deep if we 

 add 200 feet for the supposed depth of alluvial deposits. 



The cause of the exceptional grinding power of the 

 glacier in this part is very clear. From the Grimsel 

 downwards all the lateral tributaries are short, but just 

 where the valley widens above Innertkirchen, the Urbach 

 valley opens from the south, bringing the outflow of the 

 Gauli glacier, and a little farther on a large valley opens 

 from the north-east, having a drainage area about equal 

 to that of the Aar itself, and which must have nearly 

 doubled the size of the main ice-stream by the tributaries 

 from the Trift, the Susten, and the Titlis glaciers. The 

 effect of these great inflows from different directions must 

 have been to cause a heaping up of the ice, and to give it 

 an eddying motion.^ thus producing the powerful grinding 

 tool which hollowed out the rock-basin above the Kirchet. 

 The influx of this great ice-stream from the north-east 

 will also explain the curious abruptness of the Kirchet 

 hill, which, almost like a wall, blocks up the valley, and 



^ Some writers object that there is no evidence of eddies occurring in 

 ice. But Mr. E. J. Garwood, in his paper on the Glacial Phenomena 

 of Spitzbergen (Q.J.G.S., Nov. 4, 1899, p. 683), actually observed 

 eddies in the glacier. He says : "In places also eddies may be 

 observed distinctly comparable with the swirl of river water in the 

 neighbourhood of submerged rocks, so that, even where no rock is 

 visible, the presence of buried mountain ridges may often be inferred." 



