246 FRAGMENTS OF SCIENCE 



valley at this place, damming the river which came from 

 the mountains 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 Tie- 

 fenkasten 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 Kosegg 

 valley, about twenty minutes below the end of the Rosegg 

 glacier, and about an hour from Pontresina. The valley 

 here is crossed by a pine-covered moraine of the noblest 

 dimensions; in the neighborhood 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 con- 

 vince any person possessing an educated eye. Where, 

 moreover, the interior of the mound is exposed, it exhib- 

 its moraine-matter detritus pulverized by the ice, with 

 bowlders 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- 



