CHAP. Till.] THE CAUSES OF GLACIAL EPOCHS. 
145 
conception of the influence of such great changes on climate, we 
are the better able to appreciate the tendency of lesser changes 
such as have undoubtedly often occurred. 
Land as a barrier to ocean currents.-^-We have seen already the 
great importance of elevated land to serve as condensers and 
ice-accumulators ; but there is another and hardly less important 
effect that may be produced by an extension of land in high 
latitudes, which is, to act as a barrier to the flow of ocean 
currents. In the region with which we are more immediately 
interested it is easy to see how a comparatively slight alteration 
of land and sea, such as has undoubtedly occurred, would produce 
an enormous effect on climate. Let us suppose, for instance, 
that the British Isles again became continental, and that this 
continental land extended across the Faroe Islands and Iceland 
to Greenland. The whole of the warm waters of the Atlantic, 
with the Gulf Stream, would then be shut out from Northern 
Europe, and the result would almost certainly be that snow 
would accumulate on the high mountains of Scandinavia till 
they became glaciated to as great an extent as Greenland, and 
the cold thus produced would react on our own country and 
cover the Grampians with perpetual snow, like mountains of 
the same height at even a lower latitude in South America. 
If a similar change were to occur on the opposite side of 
the Atlantic very different effects would be produced. Suppose, 
for instance, the east side of Greenland were to sink consider- 
ably, while on the west the sea bottom were to rise in Davis’ 
Strait so as to unite Greenland with Baffin’s Land, thus stopping 
altogether the cold Arctic current with its enormous stream of 
icebergs from the west coast of Greenland. Such a change 
might cause a great accumulation of ice in the higher polar 
latitudes, but it would certainly produce a wonderful ameliorat- 
ing effect on the climate of the east coast of North America, 
and might raise the temperature of Labrador to that of Scot- 
land. Now these two changes have almost certainly occurred, 
either together or separately, during the Tertiary period, and 
they must have had a considerable effect either in aiding or 
checking the terrestrial and astronomical causes affecting climate 
which were then in operation. 
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