CHAPTER X 
Cause of the Glacial Period 
EXPLANATION TO ACCOMPANY PLATE IX 
Part I. 
T has been shown in previous pages! how a general elevation of the earth’s crust extending 
from the Gulf of Mexico all round the North Atlantic to an extent of several thousand feet 
has taken place towards the close of the Tertiary period, and that such elevation commenced in 
the Pliocene epoch, and was followed by subsidences of the land which have left their vestiges 
in the form of raised sea-beaches at various places and levels throughout the British Islands, Scandinavia, 
and North America. 
It is impossible to conceive that such a great uprise of the crust could have taken place without pro- 
ducing effects on the climate and temperature of the regions which came within its influence. And when we 
ask ourselves what must have been the character of these effects, the answer is inevitable ; namely, a fall 
of temperature and influx of colder climatic conditions than before or after the uprise. At the present 
day, in whatever part of the globe we make the inquiry, even in regions under the Equator itself, a rise 
in elevation above the sea-level is accompanied by increase of cold. Thus in Africa the great volcanic 
mountain of Kenia, which reaches an elevation of 18,370 feet, almost under the Equator, is covered by 
snow down to over 3000 feet from its summit.? But in order that the British Isles should be shrouded 
in perpetual snow a comparatively small additional elevation would bring them into that condition, 
as the summits of our highest mountains in Scotland, Wales, and Ireland reach elevations not far below 
the snow-line.® 
The concurrence in time of the Glacial epoch with that of the Pliocene and Post-Pliocene is 
sufficient evidence that the former was the direct result of the conditions which prevailed in the latter ; 
in other words, that the extreme cold was due to the elevation of the land. But in addition to this 
result there is to be added another effect of the uprise ; namely, the variation in the temperature and 
direction of the Gulf Stream, which has through so many ages powerfully influenced the climate of the 
British Isles and Western Europe ; and to this result we shall now proceed to direct our attention. 
Part I].—Tue Guir STREAM 
During the uprising of the Antillean continent, that branch of the great equatorial current which 
now enters the Caribbean Sea and passes on into the Gulf of Mexico must have pursued a very different 
course from that of the present day. Its passage into the Gulf was debarred by the coast of high 
continental land, the direction of which must have caused the current to pass directly northwards into 
the North Atlantic, as shown on the accompanying map (Plate IX.). ‘Such a change in direction would 
1 See also Chapter 1X., by Professor Spencer. 2 Geographical Fournal, iv. pp. 413 et seq. 
3 If Ben Nevis and Ben MacDhui were a few hundred feet higher, they would be snow-capped all the year round, 
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