ON EARTHS AND STONES. GO7

under them, is more than equal to the harm they do
by taking up room. JFlints are, also, frequently found
imbedded in chalk under the ground. Those used in
the Staffordshire potteries chiefly come from the
chalk-pits near Gravesend. So much for flints. You
have seen white pebbles, which are semi-transparent,
and, when broken, resemble white sugarcandy. ‘They
are common on the sea-shore, and mn beds of rivers.

ff, O, yes. Weeall them fire-stones. When they
are rubbed together in the dark, they send out great
flashes of light, and have a particular smell,

“2. ‘true. The proper name of these 1s quartz. It
is found in large quantities in the earth, and the ores
ot metals are often imbedded in it. Sometimes it is
periectly transparent, and then it is called erystal.
Some of these crystals shoot into exact mathematical
figures; and because many salts do the same, and are
also transparent, they are called the erystals of such
or such a salt.

G. Is not fine glass called crystal, too?

Z. It is called so by way of simile; thus we say of
a thing, “it is as clear as crystal.” But the only true
crystal is an earth of the kind I have been describing.
Well, now we come to send; tor this is properly only
quartz In a powdery state. If you examine the grains
of sand singly, or look at them with a magnifying-glass,
you will find them all either entirely or partly trans-
parent ; and, in some of the white shining sands, the
graing are all little, bright crystals.

#H, But most sand 1s brown or yellowish.

7. Uhat is owing to some mixture, generally of the
metalic kind. I beheve 1 once told you, that all
sands were supposed to contain a small portion of
gold. It is more certain that many of them contain
iron.

G. But what could have brought this quart. and
crystal into powder, so as to have produced all the sand
tm the world ?

“@ That is net very easy to determine. On the

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