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 Laggan. 
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 deflned by the moraines. 
3. The Soundings viewed in Relation to the Geological History of the 
Area, and with reference to the Origin of the Lahes. 
Loch Doine, IjocIi 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- 
