232 FKAGMENTS OF SCIENCE. 



higher up. A lake was thus formed which poured its 

 waters over the barrier. Two actions were here at work, 

 both tending to obliterate the lake the raising of its 

 bed by the deposition of detritus, and the cutting of its 

 dam by the river. In process of time the cut deepened 

 into the Via Mala ; the lake was drained, and the river 

 now flows in- a definite channel through the plain which 

 its waters once totally covered. 



From Tusis I crossed to Tiefenkasten by the Schien 

 Pass, and thence over the Julier Pass to Pontresina. 

 There are three or four ancient lake-beds between Tiefen- 

 kasten and the summit of the Julier. They are all of 

 the same type a more or less broad and level valley- 

 bottom, with a barrier in front through which the 

 river has cut a passage, the drainage of the lake being 

 the consequence. These lakes were sometimes dammed 

 by barriers of rock, sometimes by the moraines of 

 ancient glaciers. 



An example of this latter kind occurs in the Rosegg 

 valley, about twenty minutes below the end of the 

 Eosegg glacier, and about an hour from Pontresina. 

 The valley here is crossed by a pine-covered 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 

 pulverised 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 having about one-fourth of the 

 moraine to its right, and the remaining three-fourths 

 to its left. Other moraines of a more resisting charac- 

 ter hold their ground as barriers to the present day. 



