CHAP. xiir. DUE TO GLACIER-LAKES. 261 



glacier from Loch Treig then protruded itself across Glen 

 Spean, and rested on the flank of the hill on the opposite side 

 in such a manner as effectually to prevent any water from 

 escaping over the Glen Glaster '' col." The proofs of such a 

 glacier having actually existed at the point in question 

 consist, he says, in numerous cross striae observable in the 

 bottom of Glen Spean, and in the presence of moraine matter 

 in considerable abundance on the flanks of the hill extending 

 to heights above the Glen Glaster ''col." When the ice 

 shrank into less dimensions the second shelf would be formed, 

 having its level determined by the " col" last mentioned, Glen 

 Spean in the mean time being filled with a glacier. Finally, 

 the ice-blockage common to Glens Ro}^, Spean, and Laggan, 

 which consisted probably of a glacier from. Ben Nevis, gave 

 rise to the lowest and most extensive lake, the waters of 

 which escaped over the pass of Muckul or the " col" at the 

 head of Loch Laggan, which, as Mr. Jamieson has now ascer- 

 tained, agrees precisely in level with the lowest of all the 

 shelves, and where there are unequivocal signs of a river 

 having flowed out for a considerable period. 



Dr. Hooker has described some parallel terraces, very 

 analogous in their aspect to those of Glen Roy, as existing in 

 the higher valleys of the Himalaya, of which his pencil has 

 given us several grapliic illustrations. He believes these 

 Indian shelves to have originated on the borders of o-lacier- 

 lakes, the barriers of which were usuall}^ formed by the ice 

 and moraines of lateral or tributary glaciers, which descended 

 into and crossed the main valley, as we have supposed in the 

 case of Glen Roy; but others he ascribes to the terminal 

 moraine of the principal glacier itself, which had retreated 

 during a series of milder seasons, so as to leave an interval 

 between the ice and the terminal moraine. This interspace 

 caused by the melting of ice becomes filled with water and 

 forms a lake, the drainage of which usually takes place by 



