203 TWENTY-SECOND EVENING.

sea-shore, however, the incessant rolling of the pebbles
by the waves, is enough, in time, to grind them to
powder, and there is reason to believe tnat the
greatest part of what is now dry land, was once sca,
which may account for the vast beds of sand met with
inland,

G. [ have seen some stone so soft that one might
crumble it between one’s fingers, and then it seemed
to turn to sand.

T. There are several of this kind, more or less solid,
which are chiefly composed of sand, conglutinated by
some natural cement. Such are called sand-stone, or
freestone, and are used for various purposes, in building,
making grindstones, and the like, according to their
hardness.

HH, Pray what are the common pebbles that the
streets are paved with? I am sure they strike fire
enough with the horses’ shoes.

Z. They are stones of the siliceous kind, either pure
or mixed with other earths. One of the hardest ana
best for this purpose is called granite, which is of
various kinds and colours, but always consists of grains
of different siliceous earths cemented together. The
streets of London are paved with granite, brought
chiefly from Scotland. In some other stones, these
bits of different earths dispersed through the cement,
are so large, as to look like plums in a pudding, whence
they have obtained the name of pudding-stones.

G, I think there is a kind of stones that you haye
not yet mentioned—precious stones ?P

Z. These, too, are all of the siliceous class ;—--from
the opaque or half-transparent, as agate, jasper, cor-
nelian, and the like, to the perfectly clear and brilliant:
ones, as ruby, emerald, topaz, sapphire, &c.

G. Diamond, no doubt, is one of them ?P

Z. So it has commonly been reckoned, and the
purest of all; but experiments have shown, that
though it is the hardest body in nature, it may be
totally dispersed into smoke end flame, by a strong