Vice-President’s Address. 263 
Glacial Period. Consequently, from the West of Ireland 
to the Lofoten Isles, or farther north still, the evidence of 
glaciation is mainly confined to the low ground. Be that 
as it may, there must have been an excessively heavy rain- 
fall there, if there was not much snow; and although the 
low ground, in, for example, Loch Coruisk in Skye, under- 
went considerable erosion through the action of simple 
glaciers of large size, the high ground there, as in the Lofoten 
Islands, was probably never overridden by an ice-sheet for 
any lengthy period, if it was so overridden at all. I only 
refer to the matter here in order that some reference may 
be made to the time which has probably elapsed since the 
Climax of the Glacial Period. Taking into account the 
small extent of the physical changes which are known to 
have occurred since that period, I made a rough estimate in 
18871 that this time was distant from our own not more 
than 20,000 years. Observations by others, at home and 
abroad, have helped to confirm that estimate. Twenty 
thousand years is, at any rate, well within the estimates 
commonly made. 
How long the Glacial Period lasted is a question still not 
satisfactorily answered—it certainly must have been one of 
great length, if one may judge by the amount of erosion that 
was accomplished on the eastern side of the Scottish water- 
shed, where the precipitation from first to last mainly took 
the form of snow. But we do know that, although the 
valleys in the west were both deepened and widened by the 
ice, yet, as valleys, they existed long prior to the Glacial 
Period. 
The time required for the excavation of these valleys by 
the joint agency of subaerial erosion and ice has next to be 
taken into account. We have no need to attempt an 
estimate of the thickness of rock removed during the Glacial 
Period itself—and almost none has been removed since. It 
will suffice if we take the average rate of lowering of the 
surface in general at 1 foot in 3000 years instead of 1 foot 
in 6000 years as is usually done, and then, in this case, 
1 *¢Tce-Work in Edenside,” Trans. Cumberland and Westmorland Associa- 
tion, No. xi., p. 167. 
