the group to
which I wish to limit the term "crystalline," is not only thus
granulated and glittering, but is always composed of at least two,
usually three or four, substances, intimately mingled with each other in
the form of small grains or crystals, and giving the rock a more or less
speckled or mottled look, according to the size of the crystals and
their variety of color. It is a law of nature, that whenever rocks are
to be employed on hard service, and for great purposes, they shall be
thus composed. And there appear to be two distinct providential reasons
for this.

Sec. 11. The first, that these crystalline rocks being, as we saw above,
generally the oldest and highest, it is from them that other soils of
various kinds must be derived; and they were therefore made a kind of
storehouse, from which, wherever they were found, all kinds of treasures
could be developed necessary for the service of man and other living
creatures. Thus the granite of Mont Blanc is a crystalline rock composed
of four substances; and in these four substances are contained the
elements of nearly all kinds of sandstone and clay, together with
potash, magnesia, and the metals of iron and manganese. Wherever the
smallest portion of this rock occurs, a certain quantity of each of
these substances may be derived from it, and the plants and animals
which require them sustained in health.

The second reason appears to be that rocks composed in this manner are
capable of more interesting variety in form than any others; and as they
were continually to be exposed to sight in the high ranges, they were so
prepared as to be always as interesting and beautiful as possible.

And divisible into two classes, Compact Crystallines and Slaty
Crystallines.

Sec. 12. These crystalline or spotted rocks we must again separate into two
great classes, according to the arrangement, in them, of the particles
of a substance called mica. It is not present in all of them; but when
it occurs, it is usually in large quantities, and a notable source of
character. It varies in color, occurring white, brown, green, red, and
black; and in aspect, from shining plates to small dark grains, even
these grains being seen, under a magnifier, to be composed of little
plates, like pieces of exceedingly thin glass; but with this great
difference from glass, that, whether large or small, the plates will not
easily break _across_, but are elastic, and capable of being