478 
THE FRESH-WATER LOCHS OF SCOTLAND 
Blocks into which the country is divided. The evidence bearing 
on the glaciation of these areas clearly indicates that these depressions 
acted as outlets for a larger volume of ice than could have been ob- 
tained from the catchment basin of the valley containing a particular 
rock-basin. In the Northern Block, where during the maximum glacia- 
tion the ice-shed lay to the east of the existing watershed, these 
conditions must have had a marked influence on the direction and 
volume of the ice-flow. In the western part of the counties of 
Sutherland and Ross, Lochs More, Stack, Veyatie, Lurgan, Loch na 
Sheallag, and Loch Fada may be quoted as examples of lakes that 
originated under these conditions. Loch Maree is similarly situated, 
and some of the sea-lochs in that region are true fjord basins. In 
North Sutherland, where deep through valleys draining northward 
from the central plateau have been established, similar rock-basins 
are to be found, as, for instance, Loch Hope, Loch an Dithreibh, 
Loch Laoghal, Loch Naver, and Loch Coir' an Fhearna. 
It is a remarkable fact that rock-basins are extremely rare in the 
Monadhliath and Cairngorm Mountains, and the Eastern Grampians, 
where there are extensive areas of undissected plateau. In these 
regions the valleys are open and comparatively shallow ; they have an 
almost uninterrupted slope, and they lead up to lofty ground. A similar 
contrast is observable in the Southern Uplands ; for in the Moorfoot 
and Lammermuir Hills in the eastern part of that tableland, lakes 
occupying rock-basins have not been recorded, while far to the west 
among the high grounds of Galloway they are prominently developed. 
It will be shown in the sequel that the Galloway rock-basins are 
dependent upon the remarkable topographical features of that region 
which resulted in extreme differential erosion during both periods of 
glaciation. 
The distribution of many of the Scottish rock-basins further shows 
that individual lakes and even groups of lakes are ponded by rocky 
barriers that form prominent features ui the geological structure of 
the country. A remarkable series illustrating these characteristics, and 
comprising, among others. Loch Katrine, Loch Ard, Loch Chon, 
Loch Lubnaig, Loch Voil, and Loch Earn, and the upper part of 
Loch Lomond, occurs on the border of the Eastern Highlands in 
Perthshire.^ In that region the rocky barrier consists chiefly of meta- 
morphic schistose grits (the Ben Ledi and Leny grits) trending in 
an east-north-east and west-south-west direction, which are followed 
inland by weaker strata composed of phyllites and mica-schists. Loch 
Katrine may be taken as the most striking example of the group, as 
it displays in a remarkable manner certain features which, in our 
opinion, point to differential erosion by ice. In the geological notes 
1 See Appendix. 
