CALCAREOUS FORMATIONS OF THE SOLOMON GROUP. 565 



is named "Poperang" and has a height of 200 feet, the soft deposit is rarely, 

 if ever, exposed, on account probably of the small erosive power of the streams. 

 Here we find the chalky limestone containing 95 per cent, of calcium car- 

 bonate and composed of fragments of Molluscan shells and of Echinoderms, 

 with calcareous Algae, and the following Foraminifera : — Globigerina, Polytrema, 

 Carpenteria, and many Amphistegince. On the slopes also is exposed a hard 

 Foraminiferal limestone, chiefly made up of the tests of pelagic and bottom- 

 living Foraminifera, and containing 82 per cent, of calcium carbonate. The 

 Foraminifera found in specimens of this rock had crystals of calcspar in their 

 cavities ; they include the following : — Globigerina bulloides and other species, 

 G. Orbulina (uniwrsa), Pulvinulina menardii and micheliniana ',, Pullenia obliqui- 

 loculata, Planorbulina, Polytrema, Rotalia, Calcarina, &c. 



But the bulk of this islet of " Poperang " is of a unique formation, 

 which may be termed the Rhynconella limestone on account of the number of 

 Brachiopod shells of that genus that are there imbedded. This limestone may 

 be briefly described as a hard grey rock containing numbers of Brachiopod, 

 Gasteropod, and Lamellibranchiate shells. 

 with many simple corals of deep-sea J^jfcL /58k 



genera, imbedded in a calcareous matrix M & m^m /^Sbk. 



largely composed of the tests of Fora- ^^p itim ^£ggP 



minifera. I did not observe bedding in 



this limestone. Further details of the m£i^b 



imbedded organic remains and of the - ^ISP^ 



composition of the rock are subjoined. J\$mbL 3 XHUk 



The Brachiopod shells all belong to tifcllP^ — '>HS W 



the same species of Rhynconella. Mr ^ms&* 



Davidson, to whom they were submitted l, 2, m ^w, Solomon Group. 



J 3, Jih. Grayu, Fiji Island. 



for examination, is inclined to look upon 



them as belonging to Rhynconella Grayii, a species represented hitherto 

 by a single specimen discovered in the British Museum amongst other 

 natural history objects from the Fiji Islands (?) collected by Mr J. 

 M'Gillivray. This unique specimen was described by Mr S. P. Wood- 

 ward and figured by Mr Davidson, in the Annals arid Magazine of 

 Natural History as far back as 1855 (vol. xvi. p. 444, plate 10, fig. 16). 

 Since that time no other recent specimen has been discovered. Hence 

 has arisen the difficulty in pronouncing as to the identity of species since the 

 comparison of a number of fossil specimens with a single recent living one 

 does not afford sufficient material for exact determination.* I am indebted 



* The appearance of this solitary specimen of Rhynconella Grayii, which is contained in the 

 British Museum collection, might suggest its having been washed out of some recent deposit. I am 

 informed, however, by Mr Davidson that portions of the mantle, peduncle, and some muscular fibres 

 were still attached to the shell. 



