AN INTERESTING DEPOSIT. 85 



We must state that the whole of the western island 

 is covered with a capping of coral limestone, which is 

 more or less decomposed. We use the word capping " 

 advisedly ; because in any part of the island, by sinking 

 a hole of from roughly eight to fifteen feet, one comes 

 upon this peculiar soft clay, which in outward appearance 

 and behaviour is like nothing so much as Fuller's earth. 

 There is, in fact, good reason to suppose that the deposit 

 would serve the same purposes as this useful commodity, 

 which, besides being used as a toilet powder, is also 

 employed in bulk for refining crude mineral oils ; and ia 

 old days was employed by fullers in extracting the excess 

 of oil from the wool used by them in weaving cloth. 

 When placed in water this Swan Island earth behaves 

 exactly like fuller's earth ; and the deposit left at the 

 bottom of the vessel, when rubbed between the fingers, 

 gives an impression of extreme softness. Short of 

 actually trying it in practice, Mr. Allen Howe, of the 

 Geological Survey, London, could see no difference between 

 it and fuller's earth. 



At various places along the east, west, and south coasts 

 of the island, this interesting deposit can be seen cropping 

 out m the exposed cliffs at sea-level or a little above it ; 

 and there can be little doubt that it extends outwards 

 from underneath both islands as far as the limits of the 

 outlying banks. In other words. Swan Island probably 

 consists of an elevated " hogsback " of marine deposits, 

 upon which reef-building corals had grown to form a 

 capping, as soon as ever the submarine elevation had 

 reached a level at which the life of reef-building corals 

 was rendered possible. 



In a low escarpment, facing the buccaneers' earth- 

 works, at the east end of the western island, I noted one 

 day the following strata : First, a layer of two or three feet 

 of loam and soil, then from twelve to fifteen feet of coral 

 limestone, more or less decomposed ; beneath this a 

 stratum of from three to four feet of a laminated red 

 shale, and finally at the bottom of all, and commencing 



