THE TWO GREAT SCULPTORS 121 
grind the rocks underneath them, rubbing themselves 
away, it is true, but also scraping away the ground 
over which they move. In this way the glacier 
becomes a cutting instrument, and carves out the 
valleys deeper and deeper as it passes through them. 
You may always know where a glacier has been, 
even if no trace of ice remains ; for you will see rocks 
with scratches along them which have been cut by 
these stones ; and even where the rocks have not been 
ground away, you will find them rounded like those in 
the left-hand of the Frontispiece, showing that the 
glacier-plane has been over them. These rounded 
rocks are called " roches moutonnes," because at the 
distance they look like sheep lying down. 
You have only to look at the stream flowing from 
the mouth of a glacier to see what a quantity of soil 
it has ground off from the bottom of the valley ; for 
the water is thick, and coloured a deep yellow by the 
mud it carries. This mud soon reaches the rivers 
into which the streams run ; and such rivers as the 
Rhone and the Rhine are thick with matter brought 
down from the Alps. The Rhone leaves this mud in 
the Lake of Geneva, flowing out at the other end quite 
clear and pure. A mile and a half of land has been 
formed at the head of the lake since the time of the 
Romans by the mud thus brought down from the 
mountains. 
Thus we see that ice, like water, is always busy 
carving out the surface of the earth, and sending down 
material to make new land elsewhere. We know that 
in past ages the glaciers were much larger than they 
are in our time ; for we find traces of them over large 
