rue 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. He
suggests that layers of water may be formed in the glacier at right
angles with the pressure, and pass into a state of solid ice upon the
removal of that pressure, the pressure being of course relieved in
proportion to the diminution in the body of the ice by compression. The
number of blue bands diminishes as we recede from the source of the
pressure,--few only being formed, usually at right angles with the
surfaces of stratification, in the middle of a glacier, half-way between
its sides. If they are caused by pressure, this diminution of their
number toward the middle of the glacier would be inevitable, since the
intensity of the pressure naturally fades as we recede from the motive
power.

Dr. Tyndall also alludes to another structure of the same kind, which he
calls transverse structure, where the blue bands extend in
crescent-shaped curves, more or less arched, across the surface of the
glacier. Where these do not coincide with the stratification, they are
probably formed by vertical pressure in connection with the unequal
movement of the mass.

With these facts before us, it seems to me plain that the primitive blue
bands arise with the stratification of the snow in the very first
formation of the glacier, while the secondary blue ban