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G. HrGHES OX -WEST rSDIAX PHOSPHATES. 



11. Oil some AVest Ixdiax Phosphates. By G-eoe&e Hr&HEs. Esq., 

 E.C.S. Commiinicated by W. T. Bla^tfoed, Esq., LL.D., 

 F.E.S., Sec. G.S. (Bead ^s^ovember 17, 1881.) 



From: tlie specimens of TVest Indian phosphates and coral I have the 

 privilege of bringing under your notice, I desire to direct your 

 attention to the fact that, nnder 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 

 Holland'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 stiU retaining its origiual hardness and 

 composition, while the external parts had been changed from car- 

 bonate to phosphate, which, though soft and friable, stiU preserved 

 the structure and aj)pearance of the coral." 



My attention was first directed to this fact in the island of Bar- 

 buda, where I found a small vein, rich in phosphate of lime, starting 

 from the bottom of a cave in the face of a coral clifp. 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 solution, probably as phosphate 

 of potash, soda, and ammonia, and subsequently, passing through the 

 coral, caused the remarkable change in the composition of the rock 

 with which it came in contact. The specimen of stone taken 

 from this particular vein, shows that, whilst one portion remains 

 white and consists of carbonate of lime, the other portion of 

 the same stone that entered into and formed part of the vein is 

 coloured yellow from organic matter, and the carbonic acid has been 

 almost entirely replaced by phosphoric acid. 



It is, however, to the deposit found in the island of Aruba that 

 I desire to draw your special attention, because there this process 

 of phosphatizing the coral has been in operation on a most extensive 

 scale. The deposit is estimated to contain not less than 500,000 tons; 

 it occurs at the extreme point or cape of a peninsula of coral ; 

 the headland is called Sierra Colorado (or red hill), and rises about 

 300 feet above the level of the sea and about 200 feet above the 

 level of the coral that connects it with the island of Aruba. My 

 opinion is, that when this hill existed as a small island, or " cay," 

 and the coral reef between it and the then main island of Aruba 

 was submerged, it was the resort of sea-fowl, and their excrement, 

 like the bat-guano, containing soluble phos]3hates, caused the change 

 in the rock upon which it was deposited. There is no trace left of 



