From the neighbourhood of Torres Straits to about the Tropic of Capricorn, extends, at a distance of fifty to a hundred miles from the shore, an enormous bed of coral, named the Barrier Reef. There, untold millions of minute insects are still noiselessly pursuing their toil, and raising fresh structures from the depths of the ocean. Neither is this jagged belt--though deadly to the rash mariner--without its uses. In the first place, a clear channel is always found between it and the mainland, in which no sea of any formidable dimensions can ever rise, and now that modern surveys have accurately indicated where danger is to be found, this quiet channel is of the greatest use to the vessels frequenting that portion of the ocean, for they avoid the whole swell of the broad Pacific, which now thunders against and breaks harmlessly on the huge coral wall, instead of wasting its fury on the coast itself. In the second place on the Barrier Reef is found the 'Holothuria', from which the 'beche-de-mer' is prepared. It is a kind of sea-slug, averaging from one to over two feet in length, and four to ten inches in girth. In appearance, these sea-cucumbers are more repulsive, looking like flabby black or green sausages, and squirting out a stream of salt water when pressed. But despite their disgusting appearance, they are a most valuable cargo, from the high price they fetch in the Chinese market, where they are a much-esteemed delicacy. The vessel that goes in quest of 'beche-de-mer' takes several expert divers--usually Kanakas, or South Sea Islanders--and having arrived at the ground they propose fishing, a sort of head-quarters is established on some convenient island, where vegetables are planted, to stave off the scurvy that would otherwise soon attack the adventurers. This done the little vessel proceeds to the edge of the reef, and begins work in earnest.