Some of the islands are turned to profitable account by the export of guano. On Raine Island, so extensive are the deposits of guano that a railroad has been built to facilitate handling the product.

Bêche-de-mer, or trepang, is a name applied to the flesh of certain sea slugs or sea worms found in the Indian seas. Of this substance great quantities are gathered annually. In the water the animals resemble huge cucumbers, and they are therefore sometimes called "sea-cucumbers." They are found clinging to the rocks below low-water mark, and are from one to four feet in length. Their food consists of microscopic shell-fish which live upon the coral rocks.

The Great Barrier Reef of Australia, the most remarkable animal structure in the world
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The trepang exported from this section requires considerable care in preparation. After being gathered from the rocks they are cleaned, boiled, and partly dried in the air; then they are smoked with mangrove wood until dry and hard. The best class of trepang is packed in tin cases to keep it perfectly dry, as moisture ruins it. The product is marketed chiefly at Hongkong, where it is used in making the gelatinous soups for which the Chinese are so famous.

The pearl-shell fisheries yield products of considerable value. The average depth from which the mother-of-pearl shell is gathered is seven or eight fathoms. Twenty fathoms represents the greatest depth in which divers, even in their diving suits, can work, so great is the pressure of the water upon them.

The fishery is carried on chiefly for securing the shells, the finding of pearls being of secondary importance, since only about one shell in a thousand contains a pearl of much value. The shells themselves bring in the market from three hundred to eight hundred dollars per ton according to quality and size, and are used chiefly for making buttons and small ornaments.

The Cairn Cross Islands, a little coral group midway between Cape Grenville and Cape York, are especially interesting as the home and nesting-place of the Torres Strait pigeons. These large white pigeons are highly esteemed for the table. They gather at the islands during the month of October and remain until the end of March. The nests are usually built in the forked branches of the mangrove trees that form extensive thickets along the coast. Each nest contains two white eggs.

The Australian jungle-fowl or scrub-hen also frequents these islands as well as the mainland. The nests of these birds are large and unique. They consist of huge mounds of dead leaves, grass, sticks, and soft earth piled together by the adult birds in shaded and sequestered places. The mounds are about twenty feet in diameter and from ten to fifteen feet high. Several pairs of birds generally unite in their construction.