566 H. B. GUPPY ON THE RECENT 



to Mr Davidson for the accompanying figures of the fossil and living speci- 

 mens. The Gasteropod and Lamellibranchiate shells are such as live in the 

 shallow waters at the present day. A few Pteropod shells occur in the rock 

 belonging to Hyalcea ; and some Serpula tubes are also found. The Simple 

 Corals belong to the deep-sea genera, Leptocyathus, Stephanophyllia, Odonto- 

 cyathus, Flabellum, &c. ; but since the shells with which they are associated 

 are of shallow- water habit, as I am informed by Mr E. Smith, this limestone 

 would appear to be a comparatively shallow-water deposit. The Foraminifera 

 forming largely the matrix of the rock include the following pelagic 

 species : — Pullenia obliquilocidata, Globigerina hirsuta, G. cequilateralis, G. 

 Oi'bulina (universa), Pulvinulina menardii and micheliniana, &c. 



The composition of this limestone is as given below : — 



Carbonate of Calcium (75 23 per cent.) consists chiefly of Foraminiferous 

 tests of pelagic species with fragments of Echinoderms, Gasteropods, Lamelli- 

 branchs, and Brachiopods. 



Residue (24*77) consists of — 



(a) Minerals (10 - 00); felspars, augite, hornblende, and glassy fragments ; 



often surrounded by a red coating, apparently a silicate. 



(b) Siliceous Organisms (1177), a very large number of casts of the 



Foraminifera of a red colour. 



(c) Fine Washings (3 - 00), broken parts of Foraminiferous casts. 



Such then are the characters of this limestone rock. The occurrence in it 

 of a species oiRhynconella closely allied to, if not identical with, a species that 

 is represented only by a solitary specimen which was described thirty years 

 ago, is one of the more noticeable features in connection with this rock. 

 Another feature is the imbedding of corals belonging to deep-sea genera in a 

 comparatively shallow-water deposit. 



Coming now to the outer line of barrier-reef (marked C in the section) it 

 will be sufficient to describe it as formed in great part at the present sea-level. 

 The elevated portion, which has been raised some twenty feet above the sea, 

 is formed in many places of massive reef-corals imbedded in the position of 

 growth. 



Choiseul Bay. 



The large island of Choiseul, as viewed in profile from the islands of 

 Bougainville Straits, has the appearance of a level-topped ridge destitute of 

 peaks, and not elevated more than from 1500 to 2000 feet above the sea. A 

 line of barrier-reef skirts the west end of the island and encloses Choiseul Bay 

 which receives the waters of three large streams that flow through wide bolts 

 of mangrove swamps in the lower parts of their courses. About half a mile 



