242 THE EARTH MADE READY FOR MAN 



was not great, but the winters grew colder and colder. 

 In time they became so severe that even the summer 

 sun was not hot enough to melt away all the snow 

 that had accumulated during the long, cold winters. 



First the mountains became snow-capped. Then, 

 as the cold grew more intense, the snow caps grew 

 until great bodies of ice commenced to flow down the 

 mountain sides and into the valleys. Rivers of ice 

 these were, not rivers of water which had been frozen 

 into ice, but rivers composed of ice, which flowed 

 down the mountain sides with a great force. 



There are a few such ice rivers still left upon the 

 world. We call them glaciers. They are not at first 

 rivers of solid ice; they start as rivers of snow, that 

 kind of hard, icy snow that we see left on the ground 

 in the spring. They are pushed on with such a force, 

 however, that the icy snow is soon pressed into a 

 compact mass of ice which really flows slowly along 

 over the ground, scouring for itself a bed out of the 

 solid rock. 



If you take up a handful of snow and press it hard, 

 you will soon have a ball of ice instead of a snow- 

 ball. So the enormous pressure of the snow accumu- 

 lating above, forces the icy snow out from beneath, 

 and then presses that into ice as it slowly creeps 

 down the mountain side. 



You remember what a power snow has to stop a 

 railroad train. Yet when snow moves as it does in 

 a glacier its power is much more tremendous, for 

 then nothing can stop it. It pushes everything out 

 of its way, and grinds rocks to powder. 



Think what a mighty force a sheet of ice half a 



