120 THE FAIRY-LAND OF SCIENCE. 
where the stones at the side come from ; for we have 
seen that damp and frost cause pieces to break ott 
the surface of the rocks, and it is natural that these 
pieces should roll down the steep sides of the moun- 
tains on to the glacier. But the middle row requires 
some explanation. Look to the back of the picture, 
and you will see that this line of stones is made ot 
two side rows, which come from the valleys above. 
Two glaciers, you see, have there joined into one, and so 
made a heap of stones all along their line of junction. 
These stones are being continually, though slowly, 
conveyed by the glacier, from all the mountains along 
its sides, down to the place where it melts. Here it 
lets them fall, and they are gradually piled up till 
they form great walls of stone, which are called 
moraines. Some of the moraines left bv the larger 
glaciers of olden time, in the country near Turin, form 
high hills, rising up even to 1 500 feet. 
Therefore, if ice did no more than carry these stone 
blocks, it would alter the face of the country ; but it 
does much more than this. As the glacier moves 
along, it often cracks for a considerable way across 
its surface, and this crack widens and widens, until at 
last it becomes a great gaping chasm, or crevasse as it 
is called, so that you can look down it right to the 
bottom of the glacier. Into these crevasses large 
blocks of rock fall, and when the chasm is closed 
again as the ice presses on, these masses are frozen 
firmly into the bottom of the glacier, much in the 
same way as a steel cutter is fixed in the bottom of a 
plane. And they do just the same kind of work ; for 
as the glacier slides down the valley, they scratch and 
