258 Prof. Tyndall on the Conformation of the Alps, 



moraine of the noblest dimensions : in the neighbourhood of 

 London it might be called a mountain. That it is a moraine, 

 the inspection of it from a point on the Surlei slopes above 

 it will convince any person possessing an educated eye. Where, 

 moreover, the interior of the mound is exposed, it exhibits 

 moraine-matter — detritus pulverized by the ice, with boulders 

 entangled in it. It stretched quite across the valley, and at one 

 time dammed the river up. But now the barrier is cut through, 

 the stream leaving about one-fourth of the moraine to its right, 

 and the remaining three-fourths to its left. Other moraines of 

 a more resisting character hold their ground as barriers to the 

 present day. In the Val di Campo, for example, about three- 

 quarters of an hour from Pisciadello, there is a moraine com- 

 posed of large boulders, which interrupt the course of a river 

 and compel the water to fall over them in cascades. They have 

 in great part resisted its action since the retreat of the ancient 

 glacier which formed the moraine. Behind the moraine is a 

 lake-bed, now converted into a meadow, which is quite level, and 

 rests on a deep layer of mould. 



At Pontresina a very fine and instructive gorge is to be seen. 

 The river from the Morteratsch glacier rushes through a deep and 

 narrow chasm which is spanned at one place by a stone bridge. 

 The rock is not of a character to preserve smooth polishing ; but 

 the larger features of water-action are perfectly evident from top 

 to bottom. Those features are in part visible from the bridge, 

 but still better from a point a little distance from the bridge in 

 the direction of the upper village of Pontresina. The hollowing 

 out of the rock by the eddies of the water is here quite manifest. 

 A few minutes walk upwards brings us to the end of the gorge ; 

 and behind it we have the usual indications of an ancient lake, 

 and terraces of distinct water origin. From this position the 

 genesis of the gorge is clearly revealed. After the retreat of the 

 ancient glacier which filled this valley, a transverse ridge of 

 comparatively resisting material crossed the valley at this place. 

 Over the lowest part of this ridge the river flowed, rushing 

 steeply down to join at the bottom of the ridge the stream which 

 issued from the Kosegg glacier. On this incline the water 

 became a powerful eroding agent, and finally cut its channel to 

 its present depth. Geological writers of reputation assume 

 at this place the existence of a fissure, the " washing out " of 

 which resulted in the formation of the gorge. Now no ex- 

 amination of the bed of the river ever proved the existence of 

 this fissure; and it is certain that water can cut a channel 

 through unfissured rock — that cases of deep cutting can be 

 pointed out where the clean bed of the stream is exposed, the 

 rock which forms the floor of the river not exhibiting a 



