CHAP. VIII.] 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 harrier 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 Baflin'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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