Page:Natural History, Mollusca.djvu/49

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occur on our own shores, are very rich in this respect, and the widely-gaping Ear-shells (Haliotis) are most gorgeous.

The elegant articles called cameos, so much used as clasps and brooches, are formed out of the substance of large shells: the ponderous Helmets (Cassis) of the West Indies are chiefly used for this purpose. A great excellence in the art consists in the careful cutting away of the material so that the ground shall display one colour, commonly a dark hue, while the design is carved in another, commonly the pure white, which overlays the brown.

Shells, being composed of carbonate of lime, are capable of being burned to a quick-lime, having all the essential properties of that made from stone. On some parts of our own shores where limestone is scarce, shell-lime is extensively burned; but in other countries, as Holland and the United States of America, scarcely any other is used, either for building purposes or for manuring land.

Among the subordinate uses of shells may be mentioned that in China and Japan the valves of a sort of Oyster (Placuna), which are as large as a plate, flat, and transparent, are used in windows and for other purposes where we employ glass; and among the semi-barbarous of Africa, a little species of Cowry (Cypræa moneta) is universally recognised as a money currency. The natural secretions of the Mollusca are not much used among us. The Indian ink used by artists is generally understood to be in part, at least,