The secondary blue bands
intersect the planes of stratification at every possible angle, and may
therefore seem identical with the stratification in some places, while
in others they cut it at right angles. It has been objected to my theory
of glacial structure, that I have considered the so-called blue bands as
a superficial feature when compared with the stratification. And in a
certain sense this is true; since, if my views are correct, the glacier
exists and is in full life and activity before the secondary blue bands
arise in it, whereas the stratification is a feature of its embryo
condition, already established in the accumulated snow before it begins
its transformation into glacier-ice. In other words, the veined
structure of the glacier is not a primary structural feature of its
whole mass, but the result of various local influences acting upon the
constitution of the ice: the marginal structure resulting from the
resistance of the sides of the valley to the onward movement of the
glacier, the longitudinal structure arising from the pressure caused by
two glaciers uniting in one common bed, the transverse structure being
produced by vertical pressure in consequence of the weight of the mass
itself and the increased rate of motion at the centre.
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