546 H. B. GUPPY ON THE RECENT 



exposed. The numerous islets formed on the coral reefs at the present sea- 

 level do not come within the province of this paper.* 



The methods employed by Mr Murray in the examination of these recent 

 rocks are similar to those which he employed in examining the deep-sea 

 deposits obtained in the "Challenger" and other Expeditions. The Carbonate 

 of Calcium was determined by estimating the carbonic acid, weak and cold 

 hydrochloric acid being used for this purpose. The part insoluble in the acid 

 is designated "Residue" which by washing and decantation is separated, on 

 account of the different densities of its constituents, into three parts — [a) 

 Minerals, the contraction m. di. indicating their mean diameter in millimetres ; 

 (b) Siliceous Organisms, including also the glauconitic casts of Foraminifera and 

 of other calcareous organisms ; (c) Fine Washings, including those particles 

 which, resting in suspension, pass with the first decantation. The numbers in 

 brackets indicate the percentage in the whole deposit.t In addition to the 

 foregoing method, sections of many of the rocks were employed in their ex- 

 amination. 



The Island of Ugi. 



The island of Ugi, which is six miles in length and between two and two 

 and a half miles in breadth, rises to an elevation of about 500 feet above the 

 sea. From some points of view it has the profile of a broad-brimmed hat, due 

 to a pause in the elevating movement when the land was 200 feet lower than 

 it is at present ; but more commonly, losing its hat-shape, it appears as a level- 

 topped island rising gently from the sea. Fringing reefs skirt the greater por- 

 tion of its coast. 



Its geological structure may be briefly described as composed in mass of a 

 soft earthy bedded deposit, resembling the " volcanic muds " of the " Chal- 

 lenger " soundings, containing numerous Foraminifera, and encrusted near the 

 coast by coral limestone which almost disappears in the higher regions. 



The Coral Limestone. — Referring for a moment to the low-lying sea border 

 of this island, which, elevated between 2 and 8 feet above the sea, is com- 

 posed of calcareous sand, shells, and coral debris imperfectly mixed with soil, 

 I pass on to the description of the coral limestone crust. This rock is 

 occasionally exposed at the coast in cliffs not exceeding 16 or 18 feet high. 

 In the northern part of tho island I found an eminence of this coral rock rising 



* In the examination of these calcareous rocks, as well as in the preparation of this paper, I have 

 been assisted by Mr John Mukray, to whom, as well as to the Abbe Renard, I have to express my 

 indebtedness. I also desire to express my thanks to Mr Murray's assistants in the "Challenger 

 Office, Mr Fred Pearcey and Mr James Chumley. 



t For further information on this subject vide a paper on "The Nomenclature, Origin, and Du 

 tribution of Deep-Sea Deposits," by JonN Murray and A. Rexard, in the Proceedings of the R< 

 Society of Edinburgh, 1883-1884, pp. 504-50G. 



