i88o.J 
On Water and Air. 
323 
changes its form under pressure, and so readily unites when 
broken, can be forced through narrow gorges, and can 
accommodate itself to the bendings of the valley through 
which it moves. 
And now we have to dwell a little upon certain phenomena 
connected with this motion. And, first of all, with regard 
to these curious masses which are heaped up sometimes 
upon the glacier and sometimes at the side of the glacier, to 
which the name of “ moraines ” is given. You cannot have 
a better example of the origin of these moraines than you 
have here upon this Mer de Glace. The mountains bound- 
ing the glaciers are incessantly sending down stones and 
debris of all kinds which have been loosened by the frost or 
by the rain. These tumble down upon the sides of the 
glacier, and form what is called “ lateral moraines.” You 
sometimes find great heaps of matter thrown from the 
mountains, and the quantity depends upon the friability of 
the mountains. You find these great masses of stones and 
debris thrown down along the edges of the glacier. Well, 
now what follows ? I will carry you up to that rock which 
is called the Grand Rognon, which is associated with the 
Glacier du Geant. You must imagine the surface of that 
Grand Rognon covered with this debris , which has fallen 
from this rock upon the ice. That ice is for ever moving 
forwards, and what occurs ? Here, at the end of the Grand 
Rognon, you have a ridge of debris carried down by the 
moving ice, and you can trace it all along the Glacier du 
Geant down to Trelaporte. We have it marked b on the 
map (Fig. 30). Again, another moraine starts from a point 
of the Aiguille Noire (it is marked c on the map), and, 
coming down through the Glacier du Geant, you can trace 
it through the Mer de Glace. Another starts from that 
cascade just upon the Telefre, and you can see it come down 
there. And when these moraines unite together upon the 
trunk glacier they form these lines ( e , d, e) that you see here, 
not on the side, but in the middle of the glacier, and hence 
they are called “ medial moraines,” so that the side moraines 
of the tributary glaciers are converted into the . medial 
moraines of the trunk glacier. A moment’s reflection will 
make it clear to you that the number of medial moraines on 
the trunk glacier must be one less than the number of 
lateral moraines on the tributaries. Two lateral moraines 
form one medial moraine, three form two, four form three, 
and so on. , 
Well, so much for these moraines. When you come to 
visit the glaciers themselves, you may look down from a 
