COLD AND ICE ON THE EARTH 



(which would turn to falls of snow in the mountains) is 

 less than it has been. It is certain that a shortage of 

 winter rain over a number of years in succession would 

 account for the shrinkage of the glaciers, but it is not by 

 any means certain that a number of dry winters will not 

 be followed by wet ones, in which case the glaciers would 

 increase again. Some of the glaciers show that during 

 their existence they have shrunk and lengthened altern- 

 ately like gutta-percha in a variable climate. How do we 

 know that they have shrunk and lengthened? The 

 moraines of which we have spoken give us the testimony. 

 As a glacier shrinks either in length or in breadth and 

 depth it leaves the blocks of rock at its edges stranded on 

 the sides of the valley. Such perched blocks or erratics 

 are the best of glacier marks, and their great size, some of 

 them as large as a cheap villa residence, is such that no 

 current of water could have brought them there. They 

 are often poised on the tops of crags, on the very edges of 

 precipices, or on steep slopes, where they could never have 

 been left by any flood, even had the flood been able to 

 move them. The only thing that could have carried 

 them must have been a vehicle that moved very, very 

 slowly and deposited them very, very gently in fact, 

 glacier ice. We can see blocks like this on the glaciers 

 now, and others stranded at the sides. In the Swiss 

 valleys the scattered ice-borne boulders may be seen by 

 hundreds far above the glaciers and far beyond the places 

 where the glaciers end. We knozv they must have been 

 left by glaciers, and by inference we surmise that when we 

 find a valley filled with them, then, though the valley 



