38 



GRIESBACH: GEOLOGY OF THE CENTRAL HIMALAYAS. 



Their origin is clear enough; huge fans from side valleys have 

 partly dammed up the main valley, met on the other side by the talus 

 of the opposite hill range. The trickling stream which flows through 

 the valley (a tributary of the Hop Gddh) has forced a narrow outlet 

 at the third (the lowest dam), but in the case of the two upper lakes 

 (the larger one) the drainage is effected partly by overflow over the 

 dams, and partly by filtration through the debris which form them. 

 At the foot of the Manirang pass in the Spiti valley, at the 



western slope, leading up to the small glacier 

 which descends from the pass is an instruc- 

 tive example of a small lake formed by the damming up of a valley 

 by the moraine left by a former glacier (see fig. 7). A well- 



Spiti valley. 



Fig. 7. Glacial Lake at the foot of the Manirang Pass in Spiti. 



defined and broad dam, being the end moraine of a glacier, closes 

 the valley now partially, whilst the talus from the inclosing hills 

 bars the intervening space left. Immediately above, the valley is 

 filled, forming thus a small lake, about | mile long by i mile broad. 

 The dam, or end moraine, exactly marks the spot to which once the 

 Manirang glacier must have extended,— about five miles below the 

 present limits of the glacier. 

 ( 38 ) 



