564 II. B. GUPPY ON THE RECENT 



Residue (4-24), yellowish-red in colour, consists of — 



(a) Minerals (2 - 00) m.«di. 01 mm.; magnetite, felspar, hornblende, augite, 



a few casts of small Gasteropod and Lamellibrancliiate shells, and 

 many little spheres. 



(b) Siliceous Organisms, none noticed. 



(c) Fine Washings (2 - 24), a reddish argillaceous and fiocculent material 



and fine mineral particles. 



Another sample of this chalky coral limestone, which was made up chiefly 

 of decomposed coral and calcareous Algaj and held 9923 per cent, of car- 

 bonate of calcium, approaches to a magnesian limestone, on account of the 

 considerable amount of magnesia which it contains.* In a third sample the 

 only recognisable organisms are calcareous Algre. 



As one proceeds further inland along the crest of the ridge, which pursues 

 a very uniform direction, the chalk-like coral limestone is left behind ; and 

 rising gradually with the ridge crest to from 300 to 350 feet above the sea, one 

 finds a yellowish-brown Foraminiferous limestone taking its place, both capping 

 the ridge and overlying the soft deposit. The following are its characters : — 



A hard compact Foraminiferal limestone, of a yellowish-brown colour. A 

 few simple corals are imbedded in this rock, but the bulk of it is made up of 

 pelagic and bottom-living Foraminifera. 



Carbonate of Calcium (76*69 per cent.) consists of Echinoderm fragments, 

 Pteropod shells, and Foraminifera, as follows : — Globigerina bulloides, G. 

 hirsuta, G. Orbulina (universa), Pulvinulina menardii, Carpenteria, Nodosaria, 

 and Amphistegina. 



Residue (23-31), consists of — 



(a) Minerals (6"00) m. di. 0*4 mm. ; mica, a few perfect crystals of quartz, 

 • felspar, augite, and glassy fragments. 



(b) Siliceous Organisms (10-00), perfect casts of the Foraminifera of a 



reddish colour. 



(c) Fine Washings (7'31), broken down parts of casts of Foraminifera and 



a few fine mineral particles. 

 In the elevated barrier-reef through which the section passes, somewhat 

 similar rocks are displayed. In this islet (marked B in the section), which 



* I)r Leonard Dobbin, who determined for Mr Murray the carbonate of lime in the rock samples, 

 writes: — "1 would draw your attention to the result obtained in the case of the sample 'Shortland 

 Island, No. 587,' where the usual calculation, from the observed weight of carbonic acid, seems to 

 indicate an almost theoretical composition of calcium carbonate. As our method could not give such a 

 result with pure calcium carbonate (the results being in every case at least 2 per cent, too low), I tried 

 to find out the cause of this rather anomalous result. The first and most likely explanation was that 

 tin; specimen contained considerable quantities of magnesium carbonate, and I find that is the con 

 explanation, as I found on examining it that a good deal of magnesia is present. I may add that the 

 carbonic acid is not liberated from this specimen with anything like the rapidity with which il is 

 liberated from the other specimens." 



