4 
Proceedings of the Royal Society of Edinburgh. [Sess. 
of the Glacial Epoch with special reference to its changes of climate. 
Selecting Scotland as the region which he had closely studied, he described 
in detail the evidence furnished by the rock striations ; the successive 
boulder clays; the deposits of silt, clay, sand, and gravel, with land plants 
and mammalian remains, and occasionally with marine shells ; the rock- 
hound basins ; the ancient glacial lake of the Clyde with its overflow 
channels ; the raised beaches and the peat mosses. 
From these various lines of evidence he inferred that, during the Ice 
Age, Scotland witnessed several revolutions of climate. The boulder clays, 
from their inherent character, pointed to the operation of land ice. The 
interglacial beds indicated the recurrence of milder conditions, not once 
only, but several times, when the ice retired, if it did not wholly disappear. 
In this connection he laid special emphasis on the section at Woodhill 
Quarry, Kilmaurs, in Ayrshire, where a thin peaty layer intercalated in 
boulder clay yielded the remains of mammoth and reindeer, the peat 
being overlain by a band containing Arctic marine shells. As regards the 
disputed question of the origin of rock-bound basins, he was a strenuous 
supporter of Ramsay’s theory that they had been eroded by glacial action. 
He further maintained that in post-glacial time Britain was joined to the 
continent by the uprise of the floor of the North Sea. The climate then 
was continental. Ancient forests flourished whose remains are now found 
in our peat mosses. Such evidence was regarded as proving oscillations 
of climate after the ice-sheets had passed awaju 
This detailed account of the Ice Age in Scotland was of the highest 
value, because it revealed the mode of investigating and the principles 
of interpreting glacial phenomena in any highly glaciated region where 
glaciers no longer exist. Moreover, through the whole historical account 
runs the principle which James Geikie believed to be fundamental, that 
the Glacial Epoch was not one continuous age of ice, but consisted rather 
of a series of alternate cold and genial periods. 
These alternations of climate during the Ice Age seemed to harmonise 
with Croll’s theory of the cause of the great lowering of temperature in 
late Tertiary and post-Tertiary time. Croll’s hypothesis was founded on 
variations in the eccentricity of the earth’s orbit, combined with the pre- 
cession of the equinoxes, together with certain physical agencies, such as 
the deflection of ocean currents, which arise indirectly from these cosmical 
causes. It was adopted by James Geikie and expounded by him in the 
successive editions of his Great Ice Age. It was supported by Sir Robert 
Ball, and, in a modified form, by Alfred Russel Wallace. For a time it 
was widely accepted in Europe, and to a limited extent in America. But 
