250 
INTERNAL STRUCTURE AND 
lines marking the annual additions to the glacier, 
as in the adjoining figure. 
But that mass of snow, before 
it reaches the outlet of the val- 
ley, is to be compressed, con- 
torted, folded, rent in a thou- 
sand directions. The beds of 
snow, which in the upper rang- 
es of the mountain were spread 
out over broad, open surfaces, 
are to be crowded into compar- 
atively circumscribed valleys, to 
force and press themselves through narrow passes, 
alternately melting and freezing, till they pass from 
the condition of snow into that of ice, to undergo, 
in short, constant transformations, by which the 
primitive stratifications will be extensively modi- 
fied. In the first place, the more rapid motion of 
the centre of the glacier, as compared with the 
margins, will draw the lines of stratification down- 
ward toward the middle faster than at the sides. 
Accurate measurements have shown that the axis 
of a glacier may move ten- or twenty-fold more 
rapidly than its margins. This is not the place 
to introduce a detailed account of the experiments 
made to ascertain this result ; but I would refer 
those who are interested in the matter to the 
measurements given in my “ Systeme Glaciaire,” 
where it will be seen that the middle may move 
