Notes on the Phosphate-Deposit of Ocean Island; with Remarks on the Phosphates of the Equatorial Belt of the Pacific Ocean

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Abstract
I. Introduction Within the tropical belt of the Pacific Ocean occur several islands containing deposits rich in calcium phosphate. The majority of these islands are situated within 10° of the Equator, and between longitudes 140° E. and 180° E. At the present day, the islands the deposits of which may be considered as of commercial importance are Angaur, Makatea (near Tahiti), Nauru, and Ocean Island. Other islands, most of which have been worked in the early days of the phosphate industry, are Baker, Howland, Phoenix, Sydney, Maiden, Christmas, Flint, Starbuck, Browse, Lacépeède, Laysan, Cornwallis, and Clipperton. Although from time to time various theories have been put forward as to the origin of these phosphate deposits, there can be no reasonable doubt that they are all due, primarily, to bird-droppings. With the one exception of Clipperton Island, the deposits consist entirely of more or less leached guano overlying a coral-floor which is, to a greater or less extent, changed by metasomatism into tricalcium phosphate. The deposits mentioned as being of commercial importance have been leached so completely that the soluble phosphates have entirely disappeared, some of the phosphate on Ocean Island, for example, containing over 90 per cent. of tricalcium phosphate (Ca 3 P 2 O 8 ). On Malden Island, where the birds still congregate, all three forms of calcium phosphate (CaH 4 P 2 O 8 , CaHPO 4 , and Ca 3 P 2 O 8 ) are found; while on Clipperton Island a mass of trachyte, about 60 feet high, rises through the coral in the south-eastern part of the island. The original structure of the trachyte

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