1874.] Climate of the Glacial Period. 463 
overwhelming that the primary causes of these great oscil- 
lations of temperature were changes in the direction of the 
earth’s axis; and, fortified by the conditions that we see 
obtain in the other planets, we may ask astronomers to re- 
consider the question of the possibility of these changes 
having taken place. Additional data respe€ting the exact 
figure of the earth have accumulated since the problem was 
last treated. The irregular figure of the earth must affect 
the result; and it is not probable that the effect of the 
attraction of the sun and the planets upon an irregular 
equatorial protuberance can cause a perfectly circular move- 
ment of the poles. None of the other movements of the 
heavenly bodies are circular, and why should this one be? 
The weak point in Lieut.-Col. Drayson’s theory is the 
assumption that the imaginary line that the pole of the 
earth traces in the heavens is that of a circle. Through 
removing the centre of that circle from the point first fixed 
by other astronomers to another, he accounts for the cold 
' of the Glacial period, but offers no explanation of the heat 
of the Early Tertiary period. He has, however, informed 
me that the curve really traced may be that of an ellipse or 
of a spiral, the time over which accurate observations 
have been made not being long enough to determine the 
exact figure. Geology teaches us that the obliquity of the 
ecliptic has been much greater and much less than it is 
now, but with the cause of these changes it cannot deal. 
This must be left to astronomy to decide, and I doubt not 
that the solution of the question will be attempted, and, 
notwithstanding its difficulty and intricacy, accomplished. 
I have now come to the end of my argument. I have 
had more than one object in view. Besides trying to make 
plain what I considered the fundamental cause of the great 
oscillations of temperature, of which we have such abundant 
proofs in geology, I desired also to indicate the vast scope 
of the enquiry that the study of the Glacial period involved. 
It is not simply a question of scratched blocks and transported 
boulders. The whole physical geography of the world has 
been affected by it. Man’s early history and his present 
distribution are intimately connected with it. Not only the 
valleys and the fiords of the north, but the great plains of 
Europe and Asia were produced by it. Even the existence 
of our continents may be due to a succession of Glacial 
periods that have from the earliest geological times dis- 
turbed the equilibrium of the earth’s figure, and the volcanoes 
and the earthquake shocks of the present day may be 
