298 TWENTY-SECOND EVENING.

lieve we had better ask our tutor about it. Will you
please, sir, to give us some information about lime?

Tutor. Willingly. But suppose, as we talked about
all sorts of metals some time ago, I should now give
you a lecture about stones and earths of all kinds,
which are equally valuable, and much more common,
than metals.

G. Pray do, sir.

H. I shall be very glad to hear it. :

7. Well, then; in the first place, the ground we
tread upon, to as great a depth as it has been dug,
consists, for the most part, of matter of various appear-
ance and hardness, called by the general name of
earths. In common language, indeed, only the soft
and powdery substances are so named, while the hard
and solid are called stone or rock; but chemists use
the same term for all; as, in fact, earth is only crumbled
stone, and stone only consolidated earth.

ff, What!—has the mould of my garden ever been
stone ?

T. The black earth, or mould, which covers the sur-
face wherever plants grow, consists mostly of parts of
rotted vegetables, such as stalks, leaves, and roots,
mixed with sand or loose clay; but this reaches only
a little way ; and beneath it you always come to a bed
of gravel, or clay, or stone, of some kind. Now these
earths and stones are distinguished into several species,
but principally into three, the properties of which
make them useful to man for very different purposes,
and are, therefore, very well worth knowing. As you
begin with asking me about lime, I shall first mention
that class of earths from which it is obtained. These
have derived their name of calcareous from this very
circumstance, calx being lime, in Latin; and lime is
got from them all in the same way, by burning them
in a strong fire. There are many kinds of calcareous
earths. One of them is marble; you know what that is?

G. O yes! our parlour chimney-piece and hearth
are marble.

ff And so are the monuments in the church,