GEOLOGICAL CHANGES. 415 



vice v-ersd. But a period of ten thousand years, long as it may 

 appear to us, is very little from a geological point of view ; 

 and we can thus understand how the remains of the hippopo- 

 tamus and the musk ox come to be found together in England 

 and France. The very same astronomical conditions which 

 fitted our valleys for the one, would at an interval of ten 

 thousand years render them suitable for the other. In this 

 case, Palaeolithic Man would date back to the warmer inter- 

 glacial times, which perhaps may explain the absence of any 

 human remains of this period in Scandinavia and Germany. 



These considerations appear also to throw much light on 

 the changes in the distribution of land and sea which took 

 place during the glacial period. Mr. Croll has pointed out* 

 that the agglomeration of ice which must have taken place, 

 as above mentioned, would materially affect the question 

 by altering the position of the centre of the earth. It 

 must be remembered that what we call the " glacial " period, 

 was rather a period of extreme conditions ; the tempera- 

 ture of the northern and southern hemispheres being much 

 more unequal than at present, and each being alternately 

 much hotter and colder. We have not as yet any means 

 of measuring the amount of ice which under these circum- 

 stances would accumulate, first at one pole and then at the 

 other ; but even under the present comparatively equable 

 conditions, Mr. Croll considers that the ice cap at the Ant- 

 arctic Pole must be at least twelve miles in thickness. The 

 Antarctic continent appears to extend from the South Pole 

 to at least latitude 70, so that it has a diameter of 2800 

 miles, and is undoubtedly covered with one continuous sheet 

 of ice. Sir James C. Eoss, after reaching the highest southern 

 latitude which has yet been attained, found himself stopped 

 by a precipitous wall of ice, which rose to a height of 180 

 feet, and effectually barred all further progress southwards. 



* Geol. Mag., July and August, 1874. 



