10 



the land was once more elevated above the sea level. This is how 

 the surface soils came into existence. 



Some time was then devoted to the consideration of the 

 animals which existed in Britain during the cold periods : the 

 mammoth, the woolly rhinoceros, the lemming, the musk ox, &c. 

 In bone caves, where skeletons of animals are frecjuently found, 

 they can often be obtained entire in places where the hjfenas have 

 not been able to get at them. But complete skeletons are usually 

 not obtained where the animal has been waslied down by a 

 river. 



There is evidence more than complete to shuw that man was 

 contemporaneous Avith the mammotli, the mastodon, and the 

 AvooUy rhinoceros. Man in those days taking ad^'antage of caves- 

 and rock shelters, fed on those animals. Bones of tlie rhinoceros, 

 split open and charred 1)y tire on a ]>rimitive hearth, liave been 

 discovered. 



Glacial periods recur from time to time. Geology furnishes 

 evidence to show that there have been many such periods, although 

 not all of them have been of the same intensity. The last glacial 

 period was a severe one, the next will be a comparatively mild one. 



The explanation of the cause of a glacial period is given by 

 Astronomy. When from any reason there is continuously, for 

 many thousands of years, a diminished s;;pply of tlie sun'.s heat to 

 tlie Northern hemisphere, a glacial condition arises in that portion 

 of the earth. This condition depends mainly upon the configuration 

 of tlie orbit of the earth at the time. At present the earth moves 

 in an elliptical orbit, which is very nearly a circle, but wliich may 

 vary to the extent of as much as 14,000,000 of miles ; the eartli 

 being by that amount farther from the sun at one time than at 

 anotlier. It is easy to see that when, for many hundreds of years 

 in succession, winters occur while the earth is at its greatest 

 distance from the sun, they are likely to be exceptional!}- severe, 

 and as the summers as short, the snow which has fallen does not 

 melt away. Hence, the polar ice-cap, growing century by century 

 larger and larger, descends to lower and lower latitudes, and what 

 is known as a " (41acial Period " results. 



