On some West Indian Phosphates

Abstract

From the specimens of West Indian phosphates and coral I have the privilege of bringing under your notice, I desire to direct your attention to the fact that, under certain conditions, it is possible for coral-stone to be converted into phosphate of lime. Dana, in his work on Corals and Coral-islands, speaking about the formation of Howland's Island, says: “Some interesting pseudomorphs occur buried in the guano of this island. Coral fragments of various species were found that had long been covered up under the deposit, and in some of which the carbonic acid had been almost entirely replaced by phosphoric acid. In such I have found 70 per cent. of phosphate of lime. In many others the change was only partial, and on breaking some of these, in the centre was usually found a nucleus or core of coral still retaining its original hardness and composition, while the external parts had been changed from carbonate to phosphate, which, though soft and friable, still preserved the structure and appearance of the coral.” My attention was first directed to this fact in the island of Barbuda, where I found a small vein, rich in phosphate of lime, starting from the bottom of a cave in the face of a coral cliff. The earth in this cave consisted of phosphatic guano formed from excrement of bats, and similar in composition to the earth that is generally found in tropical caves. The water draining from this guano-earth must have contained phosphoric acid in