structure and composition of their crystalline
mineral ingredients. In every particle of matter
to which crystallization has been applied, we
recognize the action of those undeviating laws of
polar forces, and chemical affinity, which have
given to all crystallized bodies a series of fixt
definite forms and definite compositions. Such
universal prevalence of law, method, and order
assuredly attests the agency of some presiding
and controlling mind.
A further argument, which will be more insisted
on in speaking on the subject of metallic
veins, may be founded on the dispensation
whereby the primary and transition rocks are
made the principal repositories of many valuable
metals, which are of such peculiar and indispensable
importance to mankind.
Chapter V.
Volcanic Rocks, Basalt, and Trap.
In the state of tranquil equilibrium which our
planet has attained in the region we inhabit,
we are apt to regard the foundation of the solid
earth, as an emblem of duration and stability.
Very different are the feelings of those whose lot
is cast near the foci of volcanic eruptions; to
them the earth affords no stable resting place,
but during the paroxysms of volcanic activity,
reels to and fro, and vibrates beneath their
feet; overthrowing cities, yawning with dreadful
chasms, converting seas into dry lands, and dry
lands into seas. (See Lyell’s Geology, vol. i.
Passim.)
To the inhabitants of such districts we speak
a language which they fully comprehend, when
we describe the crust of the globe as floating on
an internal nucleus of molten elements; they
have seen these molten elements burst forth in
liquid streams of lava; they have felt the earth
beneath them quivering and rolling, as if upon
the billows of a subterranean sea; they have
seen mountains raised and valleys depressed, almost
in an instant of time; they can duly appreciate,
from sensible experience, the force of
the terms in which geologists describe the
tremulous throes, and convulsive agitations of the
earth; during the passage of its strata from the
bottom of the seas, in which they received their
origin, to the plains and mountains in which
they find their present place of rest.
We see that the streams of earthy matter,
which issue in a state of fusion from active
volcanos, are spread around their craters in
sheets of many kinds of lava; some of these so
much resemble beds of basalt, and various trap
rocks, that occur in districts remote from any