THE SCOTTISH LAKES IN RELATION 
TO THE GEOLOGICAL FEATURES 
OF THE COUNTRY 
By B. N. peach, LL.D., F.R.S., and J. HORNE, LL.D., F.R.S. 
Before discussing the question of the probable origin of the rock-basins 
in Scotland, a brief account will be given of the geological structure 
of the country and of the development of its topographical features 
prior to the Ice Age. Thereafter the successive stages in the glacia- 
tion of the region will be described and their relation to the dis- 
tribution of Scottish lakes will be discussed. 
Geological Structure of Scotland 
lewisian gneiss 
In the North- West Highlands the oldest rocks are typically 
developed. Consisting of Lewisian gneisses and schists, they form a 
belt along the western seaboard of Sutherland and Ross from Cape 
Wrath to Loch Torridon, and appear in Rona, the northern part of 
Raasay, Coll, Tiree, and the Outer Hebrides. The detailed examina- 
tion of the region between Cape Wrath and the island of Raasay by 
the Geological Survey points to the conclusion that the Lewisian 
Gneiss may be resolved into (1) a fundamental complex, composed 
mainly of gneisses that have affinities with plutonic igneous products, 
and to a limited extent of crystalline schists which may be regarded 
as of sedimentary origin ; (2) a great series of igneous rocks intrusive 
in the Fundamental Complex in the form of dykes and sills. 
The rock groups of the Fundamental Complex that have affinities 
with plutonic igneous products have a more or less definite geographi- 
cal distribution ; the first district extending from Cape Wrath to 
Loch Laxford, the second from near Scourie to beyond Lochinver, 
and the third from Gruinard Bay to the island of Raasay. In the 
central area (Scourie to Lochinver) pyroxene gneisses and ultrabasic 
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