LAKES IN EELATION TO GEOLOGICAL FEATURES 473 
gravel, at a height in some cases of several hundred feet above the 
present level of the sea. Typical examples of such phenomena, 
resulting in the modification of the drainage of the country, have 
been described by Professor James Geikie as occurring on the slopes 
of the Eaglesham and Strathavon Hills, and by Professor Kendall 
and Mr Bailey on the northern declivity of the Lammermuir Hills. 
At certain localities in Scotland, as for instance at Clava, near 
Inverness, and on the west coast of Kintyre north of Machrihanish, 
deposits of clay with arctic shells are found beneath boulder clay, 
which differ ' in character and origin from the shelly boulder clay of 
Caithness, Orkney, Ayrshire, and Wigtownshire. The shelly clays at 
the former localities are marine deposits, which indicate a depression 
of the land before the maximum extension of the ice, while the shelly 
boulder clays have been formed by land ice, which in its onward 
march had previously passed over a portion of a sea floor. 
LATER GLACIATION 
During the later glaciation the centres of ice dispersion were 
wholly changed. Instead of three great areas of distribution on the 
mainland, each mountain group seems to have nourished its own 
system of glaciers. It is true that for a time the glaciers became 
confluent, and that the ice passed over intervening cols from one line 
of drainage to another. But as a rule the direction of the ice-flow 
coincided with the trend of the valley system. Thus we find that in 
certain areas the ice moved in a direction precisely opposite or 
oblique to that during the continental ice-phase. A change so 
marked seems to afford reasonable ground for maintaining that these 
glacial epochs may have been separated by an inter-glacial period. 
The phenomena characteristic of the later glaciation are typically 
developed in the Highlands. All the main valleys were filled with 
trunk glaciers fed by innumerable tributaries draining the various 
mountain groups. In the tract lying to the north-west of the 
Great Glen the glaciers seem to have reached the sea-level in nearly 
all the firths of the East Coast, and in nearly all the sea-lochs and 
sounds on the western seaboard. On the north shore of Sutherland 
the ice apparently moved out to sea, and formed a more or less 
continuous ice-front extending from the borders of Caithness west- 
wards as far as the Kyle of Tongue, while lobes of ice occupied Loch 
Eireboll and the Kyle of Durness. What may be conveniently de- 
scribed as ice-cauldrons were set up in Central Sutherland, and in the 
district of Loch Monar on the borders of Ross-shire and Tnveniess-shire. 
Even the remote Orkney and Shetland Isles, and the hills of 
Lewis and Harris in the Outer Hebrides, nourished their own 
independent glaciers. 
