kind. Blackboard crayons are made of this: so are
whitewash and whiting for cleaning silver and making putty.

Another stone that builders would be sorry to do without is slate.
This, too, was formed at the bottom of the sea. Rivers brought down
fine particles of clay, which settled, were covered by other matter,
and finally became stone. It was formed in layers, of course, but,
queerly enough, it splits at right angles to its bottom line. Just why
it does this is not quite certain, but the action is thought to be due
to heat and long, slow pressure, which will do wonderful things, as in
the case of coal. This splitting is a great convenience for the
people who want to use it for roofing and for blackboards. Blocks of
slate are loosened by blasting, and are taken to the splitting-shed.

Splitting slate needs care, and a man who is not careful should never
try to work in a slate quarry. The splitting begins by one man's
dividing the block into pieces about two inches thick and somewhat
larger than the slates are to be when finished. The way he does this
is to cut a little notch in one end of the block with his "sculpin
chisel" and make a groove from this across the block. He must then set
his chisel into the groove, strike it with a mallet, and split the
slate to the bottom. This sounds easy, but it needs skill. Slate has
sometimes its own notions of behavior, and it does not always care to
split in a straight line exactly perpendicular to the bottom of the
stratum. The man keeps it wet so that he can see the crack more
plainly, and if that crack turns back a little to the right, he must
turn it to the left by striking the sculpin toward the left, or
perhaps by striking a rather heavy blow on the left of the stone
itself. Now the chief splitter takes it, and with a broad thin chisel
he splits it into plates becoming thinner at each split. The second
assistant trims these into the proper shape and size with either a
heavy knife or a machine. Slate can be sawed and planed; but whatever
is done to it should be done when it first comes from the quarry, for
then it is not so likely to break. It would be very much cheaper if so
much was not broken and wasted at the quarries and in the splitting.
It is said that in Wales sometimes one hundred tons of stone are
broken up to get between three and four tons of good slate. Within the
last few years the quarrymen have been using channeling machines and
getting out the slate in grea