LAKES IN RELATION TO GEOLOGICAL FEATURES 471 
areas of ice dispersal there were minor centres, as, for instance, in the 
Cuillin Hills in Skye and in the Cheviots. 
The ice radiating from the three main centres coalesced on the 
intervening plains, and moved towards the Continental Shelf on either 
side. Thus the ice from the Eastern Highlands invaded the Mid- 
land Valley, and met the sheet from the Southern Uplands as far 
south as the Pentland Hills and the Lammermuirs on the east, and 
Muirkirk and New Cumnock on the west ; the confluent streams 
moving towards the North Sea and the Firth of Clyde. Again, the 
glaciers from the mountains of Ross and Inverness crossed the plain 
of the Moray Firth and invaded the coastal belt of Nairn, Elgin, 
and Banff*. 
As already indicated, the ice flowing eastwards off the mainland of 
Scotland united with the Scandinavian mer de glace on the floor of 
the North Sea. One branch of the combined ice-field moved north- 
wards from the Firth of Forth, and, skirting the coast-lines of 
Kincardine and Aberdeen, ultimately overrode Caithness, Orkney, 
and Shetland on its onward march to the Atlantic. The southern 
branch, pressed back by the Scandinavian sheet, was deflected south- 
wards, and invaded the plains of England south of Flamborough 
Head. 
On the north coast of Sutherland the ice advanced in a north- 
west direction under the influence of the mer de glace that passed 
over Caithness and Orkney. Along the western seaboard, from 
Cape Wrath to Kintyre, the general movement was outwards across 
the Continental Shelf, with important local deflections due to the 
physical features of the Western Isles. During the maximum exten- 
sion the ice from the mainland crossed the Minch and overtopped 
the Outer Hebrides ; it coalesced with the local sheet of the Cuillin 
Hills, and the combined streams surmounted the basalt plateau to 
the north of these mountains. 
South of Loch Fyne the Highland stream advanced towards the 
Firth of Clyde, where it united with the ice from the western portion 
of the Southern Uplands, and moved southwards towards the Irish 
Sea, a branch being deflected westwards across Kintyre under the 
influence of the sheet radiating from the north of Ireland. 
No reliable estimate can be given of the thickness of this extensive 
ice-field, but it must have reached great dimensions when none of 
the peaks of the mainland rose as nunataks above the surface of the 
ice, when the outlying islands were overtopped and the intervening 
sounds were occupied by the mer de glace. Professor James Geikie 
suggests that some of the mountains in Harris may have protruded 
above the ice-field. 
The phenomena attributable to the ice during the period of 
