THE TWO GREAT SCULPTORS. 119 
But this is not the chief work of ice. You will 
remember how we learnt in our last lecture that snow, 
when it falls on the mountains, gradually slides down 
into the valleys, and is pressed together by' the 
gathering snow behind until it becomes moulded into 
a solid river of ice (see Fig. 29, Frontispiece). In 
Greenland and in Norway there are enormous ice- 
rivers or glaciers, and even in Switzerland some of 
them are very large. The Aletsch glacier, in the 
Alps, is fifteen miles long, and some are even longer 
than this. They move very slowly on an average 
about 20 to 27 inches in the centre, and 13 to 
19 inches at the sides every twenty- four hours, in 
summer and autumn. How they move, we cannot 
stop to discuss now ; but if you will take a slab of 
thin ice and rest it upon its two ends only, you can 
prove to yourself that ice does bend, for in a few 
hours you will find that its own weight has drawn it 
down in the centre so as to form a curve. This will 
help you to picture to yourselves how glaciers can 
adapt themselves to the windings of the valley, 
creeping slowly onwards until they come down to a 
point where the air is warm enough to melt them, and 
then the ice flows away in a stream of water. It is 
very curious to see the number of little rills running 
down the great masses of ice at the glacier's mouth, 
bringing down with them gravel, and every now and 
then a large stone, which falls splashing into the stream 
below. If you look at the glacier in the Frontispiece, 
you will see that these stones come from those long 
lines of stones and boulders stretching along the sides 
and centre of the glacier. It is easy to understand 
