their
long sides; the Iaminas of the outer and inner layers are parallel to
the lines of growth, while those of the middle layer are at right
angles to them. In cowries there is an additional layer, which is a
duplicating of the nacreous layer, formed when the animal has attained
its full growth.
At the London Exhibition there was a very fine collection of shell cameos, from Rome, owned by the engraver Seculine.
Certain
natives of India prepare shell cameos with rude but efficient
instruments for cutting them, and the Indian department in the
Exhibition showed numerous specimens.
MOSAIC AND PIETRA DURA.
Roman, Venetian, Florentine, and other llosaics.— The art of mosaic (opus musivum of
the Romans), was originally applied only to the combination of small
dice-shaped stones (precious and common), or tesserae of the ancients,
in patterns. It has long been an important source of labor to the
inhabitants of several parts of Italy, such as Venice; and under
various modifications is now carried on in the principal cities of
Europe. The manufacture has long ceased to be confined to combinations
of tessera?, and is now understood to include all kinds of inlaid and
veneered work, in whatever material,—fragments of pseudo-precious
stones (agate, chalcedony, malachite, lapis lazuli), marbles of the
most variegated colors, porphyry, lava, granite, fluor-spar, and also
the various colored glasses (imitation gems), avanturine, and enamels,
which, when put together (sometimes in microscopical fragments), and
formed into a landscape, figures, or other design, are now called
mosaics. The richer the colors and shadings, so as to produce fine
pictures, the more striking the mosaics fall on the eye of
