worked by compressed air. After this, the stone is rubbed--by
machinery, of course--with water and emery, then by wet felt covered
with pumice or polishing putty. A few years ago two young Vermonters
invented a machine that would saw granite. This saw has no teeth, but
only blades of iron. Between these blades and the piece of granite,
however, shot of chilled steel are poured; and they do the real
cutting.

Granite has long been used in building wherever a strong, solid
material was needed; but until the sand blast was tried, people
thought it impossible to do fine work in this stone. There was a firm
in Vermont, however, who believed in the sand blast. They had a
contract with the Government to furnish several thousand headstones
for national cemeteries. Cutting the names would be slow and costly;
so they made letters and figures of iron, stuck them to the stones,
and turned on the blast. If a sand blast is only fast enough, it will
cut stone harder than itself. The blast was turned upon a stone for
five minutes. Then the iron letters were removed. There stood in
raised letters the name, company, regiment, and rank of the soldier,
while a quarter of an inch of the rest of the stone, which the iron
letters had not protected, had been cut away. By means of the sand
blast it has become possible to do beautiful carving even in material
as hard as granite.

Granite looks so solid that people used to think it was fireproof; but
it is really poor material in a great fire. Most substances expand
when they are heated; but the three substances of which granite is
made do not expand alike, and so they tend to break apart and the
granite crumbles.

A marble quarry is even more interesting than a granite quarry. If you
stand on a hill in a part of the country where marble is worked, you
will see white ledges cropping out here and there. The little villages
are white because many of the houses are built of marble. Then, too,
there are great marble quarries flashing in the sunshine. Sometimes a
marble quarry is chiefly on the surface. Sometimes the marble
stretches into the earth, and the cutting follows it until a great
cavern is made, perhaps two or three hundred feet deep. A roof is
often built to keep out the rain and snow. It keeps out the light,
too, and on rainy days the roof, together with the smoke and steam of
the engines, makes the bottom of the quarry a gloomy place. Everywhere
there are slender ladders with men ru