It will be seen, on referring to the wood-cut on page
758, where the close, uniform, vertical lines represent the true veined
structure, that at several points of that section the lines of
stratification run so nearly parallel with them, that, were the former
not drawn more strongly, they could not be easily distinguished from the
latter. Along the margins, also, in consequence of the retarded motion,
the blue bands and the lines of stratification run nearly parallel with
each other, both following the sides of the trough in which they move.
Undoubtedly, in both these instances, we have two kinds of blue bands,
namely: those formed primitively in a horizontal position, indicating
seams of stratification, and those which have arisen subsequently in
connection with the movement of the whole mass, which I have
occasionally called bands of infiltration, as they appeared to me to be
formed by the infiltration and freezing of water. The fact that these
blue bands are most numerous where two glaciers are crowded together
into a common bed naturally suggests pressure as their cause. And since
the beautiful experiments of Dr. Tyndall have illustrated the internal
liquefaction of ice by pressure, it becomes highly probable that his
theory of the origin of these secondary blue bands is the true one.
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