SNOW AND ICE. 
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stretching right across the glacier, and of course 
with the convexity upwards. 
Longitudinal crevasses occur wherever a glacier 
issues from a comparatively narrow defile into a 
wider plain. The difference of inclination checks its 
descent; it is pushed from behind, and having room 
to expand it widens, and in doing so longitudinal 
crevasses are formed. 
The sides of crevasses are of a brilliant blue, and 
often look as if they were cut out of a mass of beryl. 
The mountaineers have a traditon that glaciers will 
tolerate no impurity, and though this is not of course 
a correct way of stating the question, as a matter of 
fact the ice is of great purity. 
Veined Structure. 
Glacier ice very often looks as if it had been 
carefully and regularly raked. It presents innumer- 
able veins or bands of beautifully blue dear ice, run- 
ning through the general mass, which is rendered 
whitish by the presence of innumerable minute air- 
bubbles. The blue plates are more or less lenticular 
in structure, sometimes a few inches sometimes many 
yards in length, but at length gradually fade away. 
The whole surface of the glacier in such parts is 
lined with little grooves and ridges, the more solid 
