an arrangement constantly takes place
before our eyes in volcanic rocks as they cool. But it is not at all
easy to understand how the white, hard, and comparatively heavy
substances should throw themselves into knots and bands in one definite
direction, and the delicate films of mica should undulate about and
between them, as in Fig. 5 on page 114, like rivers among islands,
pursuing, however, on the whole, a straight course across the mass of
rock. If it could be shown that such pieces of stone had been formed in
the horizontal position in which I have drawn the one in the figure, the
structure would be somewhat intelligible as the result of settlement.
But, on the contrary, the lines of such foliated rocks hardly ever are
horizontal; neither can distinct evidence be found of their at any time
having been so. The evidence, on the contrary, is often strongly in
favor of their having been formed in the highly inclined directions in
which they now occur, such as that of the piece in Fig. 7, p. 117.[45]

[Illustration: FIG. 6.]

Sec. 5. Such, however, is the simple fact, that when the compact pact
crystallines are about to pass into slaty crystallines, their mica
throws itself into these bands and zones, undulating around knots of the
other substances which compose the rock. Gradually the knots diminish in
size, the mica becomes more abundant and more definite in direction, and
at last the mass, when broken across the beds, assumes the appearance of
Fig. 6 on the last page.[46] Now it will be noticed that, in the lines
of that figure, no less than in Fig. 5, though more delicately, there is
a subdued, but continual expression of _undulation_. This character
belongs, more or less, to nearly the whole mass of slaty crystalline
rocks; it is one of exquisite beauty, and of the highest importance to
their picturesque forms. It is also one of as great mysteriousness as
beauty. For these two figures are selected from crystallines whose beds
are remarkably straight; in the greater number the undulation becomes
far more violent, and, in many, passes into absolute contortion. Fig. 7
is a piece of a slaty crystalline, rich in mica, from the Valley of St.
Nicolas, below Zermatt. The rock from which it was broken was thrown
into coils three or four feet across: the fragment, which is drawn of
the real size, was at one of the turns, and came away like a thick
portion of a crumpled quire of paper from the other sheets.[47]

[Illustrat