Illustration: STONE QUARRY.
Stone for building is chiefly of four kinds:--lime-stone, sand-stone,
granite, and marble. Slate is never used for building, but is very
suitable for roofing. The most common stone is limestone, and that
brought from Portland Island is especially good for building-stone;
it is called Portland stone, and it is of this stone that St. Paul’s
Cathedral is built, and most of the other public buildings of London:
it is rather soft when first dug from the quarry, but hardens with
age. Sandstone is a very coarse kind of stone, and is only used
where not much exposed to the weather; it consists of grains of
sand adhering so firmly together as to form a stone of considerable
hardness. Granite is a very hard stone, and very durable; so hard
that it cannot well be carved, and is therefore only used where
durability and plain solidity are required; London Bridge and the
Euston Square Terminus of the Birmingham Railway are built of
granite. Marble is a very fine heavy kind of limestone, sometimes
quite white, and generally partly transparent; the white kind is
very expensive, and is used for statuary, that is to say, for carving
into figures, vases, &c.; it is very durable, but is too expensive
for general use. Chimney-pieces, slabs for washing-stands, and other
articles of that description, are also made of it.
Limestone, marble, and also chalk (a soft kind of limestone), all
become changed into lime if made red hot, hence the name, limestone,
is often applied to all three.
Stone quarries are those places where stone exists of a quality
suitable for building purposes, and in a situation admitting of its
easy removal. All stone, with the exception of granite and marble,
exists in layers or strata as they are called, so that the stone
can be easily split in the direction of these strata or seams. When
a large piece of stone has to be removed, wedges are driven in a
row into these seams, and when the stone has started, it is notched
at the sides and back, so that in general a square piece is thus
removed; if it be not so, it is generally made into a somewhat square
before leaving the quarry, hence the name, derived from the French
“_quarre_.” Granite having none of the lines of cleavage, as they
are called, is broken by a row of wedges driven till a crack forms
from one to the other. Slate is a clay-stone found in layers like
limestone, but much more perfect; so much so, indeed, that it can
be split into slices a quarter of an inch thick and one or two feet
square; these, when sorted into sizes, form the slates for roofing
houses. It has been much used of late in thick slabs, cut by circular
saws, for making cisterns, a purpose for which it is well adapted.