i88o.] 
On Water and Air . 
325 
appeared to rise more and more, and finally you find it there 
as a so-called glacial table. It is not due to the lifting of 
the table or to the lifting of the rock, but to the melting of 
the unprotected ice all round the rock. 
There are other cases in which protection sometimes 
comes into play in an extraordinary fashion, and there is 
nothing more interesting or more striking than what are 
called the sand cones of the glaciers. Rivers coming near 
moraines contract a certain amount of impurity, and carry 
sand along with them and distribute it over the ice ; and 
the ice protected by this sand rises not in reality, but rela- 
tively. The surrounding ice is melted away, and these 
patches of sand appear to rise up, and you have upon the 
glaciers little mountains — little sand cones as they are 
called — which might be considered to be representative of 
the Alps themselves in miniature. 
I now want to show you what occurs in consequence of 
the incessant aCtion of the sun upon the glaciers. The 
rising of the moraines and the rising of the glacier tables 
prove that when the sun aCts upon the glaciers it rapidly 
melts the ice. And what is the consequence ? Rivers, 
rivulets, and streams, of great power and impetuosity, are 
sometimes formed in the glaciers upon those portions which 
are not very much crevassed (or cut across by open chasms 
in the ice). Those rivers which come upon a crevassed 
portion of a glacier plunge into the crevasses or chasms, 
and find their way to the bottom of the glacier and roll 
along the bottom as a sub-glacial river underneath the ice, 
and finally they issue as a river from a vault of ice at the 
end of the glacier. At the end of the Mer de Glace is a 
vault of this kind, which in the summer time is exceedingly 
dangerous to enter. I remember once standing and looking 
into that vault, and thinking whether I should go into it, 
it was of such magical beauty ; and while I stood pondering 
upon the point of the prudence and possibility of entering 
it, the whole roof, weighing some 20 or 30 tons, fell down 
upon the bottom. In winter it is firm and fast, and can be 
safely entered and explored. 
As I have said, from the termination or snout of the 
glaciers a river issues, the Mer de Glace being the source 
of the Arveiron, the Rhone glacier giving birth to the River 
Rhone, and the sources of the greatest rivers in Europe can 
all be traced back to the glaciers. 
I have said that the centre of the glacier mo res more 
rapidly than the sides, and I have referred to the cre- 
vasses, as they are called. That is the technical name 
