THE FRESH -WATER LOCHS OF SCOTLAND. 45 



the ice-movement was independent of the existing valley-system. 

 Indeed, from the evidence furnished by the striae and the transport of 

 boulders, it may be inferred that the minimum thickness of the ice- 

 sheet during this period must have been not less than 3000 feet in the 

 lake district of Perthshire. 



The boulder-clay or ground-moraine, which was laid down during 

 the great glaciation, must have been extensive, for it is found at great 

 elevations, and it sometimes attains a great thickness. For instance, in 

 the lee of the ridge of Ben Vane, to the west of Loch Lubnaig, it 

 reaches a height of 2290 feet, and in places it is over 100 feet thick. 

 But a large part of this deposit was removed during the later glaciation 

 by the valley glaciers, for the relics occur above the limits of the valley- 

 moraines, the latter resting frequently on the solid rock. 



Only a brief allusion is necessary to show the development of the 

 later glaciers. The striae produced by this later movement coincide 

 generally with the trend of the existing valleys. But though this is 

 true, there is evidence to prove that even the larger valley-glaciers were 

 thick enough to overflow minor watersheds. For instance, the glacier 

 which descended the basin of Loch Katrine was thick enough to override 

 the low col between that loch and Loch Chon, while another branch 

 passed westwards by Loch Arklet towards Loch Lomond. Another 

 example of the same phenomenon might be quoted. The glacier which 

 descended the basin of Loch Voil towards Loch Lubnaig was thick 

 enough to overflow the col between Strathyre and Loch Earn, while 

 another branch ascended Glen Buckie and joined the Loch Lubnaig 

 glacier at Laggaii. 



Moraines are well developed in most of the valleys, and are fre- 

 quently arranged in concentric lines, as in Glen Finglas, north of Brig 

 o' Turk. On the south side of Loch Katrine, between the jetty and 

 Glasahoile, the moraines are distributed in parallel lines along the 

 shore of the lake. As already indicated, the upper margins of the 

 valley-glaciers are defined by the moraines. 



3. The Soundings viewed in Relation to the Geological History of the 

 Area, and with reference to the Origin of the Lakes. 



Loch Doine, Loch Voil, and Loch Lubnaig. Reference has already 

 been made to the fact that, in post-glacial time, Loch Doine, Loch Voil, 

 and Loch Lubnaig must have formed one continuous sheet of water, 

 and that their subsequent isolation has been due to the deposition of 

 sediment. 



Loch Doine has been separated from Loch Voil by alluvial cones 

 laid down by two streams, one from the north at Monachylemore, and 

 another from the south at Monachyle Tuarach. The 50-feet subaqueous 

 line has been traced round the Loch Doine basin, and the deepest sound- 



