AMONG GLACIERS RECENT AND EXTINCT. 
179 
For a long time geologists have endeavoured to account for 
this wonderful change of climate by various alterations in the 
positions of sea and land, elevation of high lands in Polar 
regions, changes in the flow of the Gulf Stream, and other geo- 
graphical modifications. Sir Charles Lyell directed attention 
long ago to the effect which the altered positions of land and 
sea must have on climate in different parts of the world, and to 
the alteration which must affect Polar regions, or any other 
regions, if high mountain ranges were elevated in the place of 
low-lying plains, or lakes, or seas. In his great work, u The 
Principles of Geology,” he discussed fully the effect of the 
Gulf Stream in modifying Arctic cold, the effect of the 
Fohn, or the south wind, now, in melting the ice of Alpine 
glaciers, and the change brought about by the elevation of the 
Sahara or Great Desert into land instead of sea, with various 
other geographical changes and conditions which do, no doubt, 
affect climate very considerably. But for some time past there 
has been a strong belief that all these phenomena combined 
were not sufficient to bring about that intensely cold period 
which for long ages held our northern hemisphere under the 
dominion of intense frost, and brought about such extraordinary 
changes of climate since the Miocene forest days of the Arctic 
regions. So strongly did Professor Heer feel this that, after 
several investigations into the history of the fossil trees and 
plants which formerly grew in Greenland, he said, “We are face 
to face with a problem whose solution must be attempted, and 
doubtless completed, by the astronomer.” And for some years 
now, astronomers, mathematicians, and physicists have endea- 
voured to solve the problem. The possibility of an alteration 
in the earth’s axis was maintained by the late Sir John Lubbock 
and M. Adhemar, and the changes which might be caused by 
variations in the eccentricity of the earth’s orbit, with other 
astronomical problems, have been calculated by Mr. Croll, Mr. 
Stone, and other mathematicians. But I must refer those in- 
terested in such questions to Mr. Cr oil’s work on “ Climate and 
Time in their Geological Delations.” I will only say that late 
physical conditions those changes produce on the climate of the 
earth. Mr. Croll believes that there have been recurring glacial 
epochs, that is to say, cold periods followed by warm periods, in 
both hemispheres, throughout all geological time. But geology 
has for some time past contemplated this question of recurring 
glacial periods. There is undoubtedly evidence of frost and ice 
action in the transported blocks which occur in conglomerates 
of the age of the Old Bed Sandstone in Scotland. Professor 
Eamsay was led long ago to infer that ice action was the only 
n2 
