_, because they possess those qualities in so
great a degree, as to entitle them, in most respects, to the rank of
alkalies. They combine and form compound salts with acids, in the same
way as alkalies; they are, like them, susceptible of a considerable
degree of causticity, and are acted upon in a similar manner by chemical
tests. --The remaining earths, silex and alumine, with one or two others
of late discovery, are in some degree more earthy, that is to say, they
possess more completely the properties common to all the earths, which
are, insipidity, dryness, unalterableness in the fire, infusibility, &c.

CAROLINE.

Yet, did you not tell us that silex, or siliceous earth, when mixed with
an alkali, was fusible, and run into glass?

MRS. B.

Yes, my dear; but the characteristic properties of earths, which I have
mentioned, are to be considered as belonging to them in a state of
purity only; a state in which they are very seldom to be met with in
nature. --Besides these general properties, each earth has its own
specific characters, by which it is distinguished from any other
substance. --Let us therefore review them separately.

SILEX, or SILICA, abounds in flint, sand, sandstone, agate, jasper, &c.;
it forms the basis of many precious stones, and particularly of those
which strike fire with steel. It is rough to the touch, scratches and
wears away metals; it is acted upon by no acid but the fluoric, and is
not soluble in water by any known process; but nature certainly
dissolves it by means with which we are unacquainted, and thus produces
a variety of siliceous crystals, and amongst these _rock crystal_, which
is the purest specimen of this earth. Silex appears to have been
intended by Providence to form the solid basis of the globe, to serve as
a foundation for the original mountains, and give them that hardness and
durability which has enabled them to resist the various revolutions
which the surface of the earth has successively undergone. From these
mountains siliceous rocks have, during the course of ages, been
gradually detached by torrents of water, and brought down in fragments;
these, in the violence and rapidity of their descent, are sometimes
crumbled to sand, and in this state form the beds of rivers and of the
sea, chiefly composed of siliceous materials. Sometimes the fragments
are broken without being pulverised by their fall, and assume the form
of pebbles, which gradually become rounded and p