CALCAREOUS FORMATIONS OF THE SOLOMON GROUP. 553 



near the centre of the island and entirely composed of this formation. This 

 was the greatest thickness that I saw exposed of this soft Foraminiferal deposit ; 

 and since this line of cliffs represented a natural section of the summit, I may 

 safely conclude that the elevated interior of the island is entirely of this forma- 

 tion, a conclusion which is supported by the existence of other sections almost 

 as extensive in that region, and one which has an important bearing on the 

 past history of Treasury Island. The beds in this line of inland cliffs dip west- 

 ward 12° to 15°; the vertical faces of the cliff being preserved by the scaling off 

 of large slabs of rock along the lines of joint which correspond with the strike 

 of the beds.* On the level summit, wherever a small rivulet exists, this soft 

 Foraminiferous deposit is exposed. I now append the description of specimens 

 of this rock obtained from the inland cliffs above referred to. 



A very friable rock, of a greenish-grey colour, containing from 3 to 10 per 

 cent, of carbonate of lime, which consists of a few Coccoliths, and the following 

 Foraminifera : — Cassidulina crassa (rare), Uvigerina asperida (few), TruncatuZina 

 lobatuZa (rare), Rotalia soZdanii (rare), PuZmnuZina elegans (rare), and fragments 

 of GZobigerince. 



Minerals, about 60 per cent., consisting of mica, quartz, magnetite, horn- 

 blende, augite, felspars, many glassy fragments, scoriae, and green fragments — 

 glauconite % 



Fine Washings, about 30 per cent., consisting of argillaceous matter, fine 

 mineral particles, glassy fragments, and fragments of scoriae. 



Note. — This rock seems to have been formed in comparatively shallow water, 

 as it is made up chiefly of the debris of volcanic rocks washed down from the 

 land, and afterwards mixed with the remains of minute organisms which live 

 near the coast. 



Deposits yet more recent than those which compose the mass of the island, 

 I found exposed in the banks of the lower parts of the streams opening 

 on the south coast. Here is displayed a bluish calcareous loam-rock con- 

 taining Foraminifera and numerous Molluscan shells. The following are its 

 characters : — 



A very friable rock. 



Carbonate of Calcium (6*52 per cent.), consists of a few Coccoliths ; frag- 

 ments of Echinoderm, Lamellibranchiate, Pteropod, and Ostracode shells ; 

 a few Alcyonium spicules ; and some Foraminifera (vide List). 



Residue (9348 per cent.), greenish-brown in colour, consists of — 



(a) Minerals (50*00) m. di. 3 mm. A great quantity of magnetite, 



* At the foot of these cliffs a rich red ochre-clay has accumulated, probably as washings from the 

 cliffs above. It contains only 15 to 20 per cent, of mineral particles, and exhibits but a very slight 

 effervescence with dilute acid. 



VOL. XXXII. PAKT III. 4 Y 



