558 H. B. GUPPY ON THE RECENT 



ments of its own substance joined together in a calcareous cement* My 

 interest was engaged in a further degree in this locality, on observing that in 

 the vicinity of the protruding mass of volcanic rock the flat was composed in 

 places, not of the ordinary reef-rock, but of a soft argillaceous light-coloured 

 rock that effervesced with an acid. Walking in a few yards from the beach I 

 clambered up a slippery slope t between huge masses of coral limestone that 

 had been detached from a line of cliffs above ; and in a few minutes I became 

 aware that I had made a discovery of some importance. A vertical precipice 

 of coral limestone, about 80 feet in height, here rested on a friable argillaceous 

 rock, light brown in colour and sparingly Foraminiferous {vide diagram of this 

 locality, PI. CXLIV. fig. 7). Appended is the description of this rock which 

 Mr Murray has given to me : — 



A friable earthy rock of a yellowish-brown colour, which, from the small 

 size of the minerals, the absence of Foraminifera that inhabit the bottom, and 

 the scarcity of pelagic forms, resembles somewhat a deep-sea clay ; and dis- 

 plays a thin coating of manganese peroxide between the small layers or folds 

 of the rock. A detached concretionary block of manganese peroxide, one or 

 two cubic feet in size, was observed by Lieut. Malan on the reef-flat on the 

 north coast of this island, not far from the locality where the clay above 

 described was met with. The typical fragment which was brought home is, 

 Mr Murray says, quite similar to smaller masses dredged by the " Challenger" 

 and Blake. 



Carbonate of Calcium (2079 per cent.) consists of Coccoliths, Globigerbia 

 hulloides, G. (Orbulina) universa, G. conglobata, Pidvinulina menardii, and a few 

 small fragments of Echinoderms. 



Residue (79"2i) reddish-brown in colour, consists of — 



(a) Minerals (35 "00) m. di. 0*08 mm., felspar, hornblende, one or two frag- 



ments of magnetite, with a few glassy fragments. 



(b) Siliceous Organisms (1*00), fragment of a sponge spicule noticed. 



(c) Fine Washings (43*21), argillaceous matter, very fine mineral particles 



and some glassy fragments. 

 Such being the characters of the deposit underlying the coral limestone, as 

 exposed in this natural section, I now come to the consideration of the coral 

 limestone itself, which is a hard compact rock resting abruptly on the soft 

 underlying deposit. Imbedded in the base of this cliff of coral limestone were 

 two dome-shaped masses of Astrrean corals of different species, one of them 



* A small patch of massive coral, which still adheres to its surface, probably found attachment during 

 the most recent upheaval of the island (vide posted). 



t This slippery slope, which is of the argillaceous rock to be immediately referred to, is in ] ait 

 encrusted by calcareous tufa, containing, at an elevation of 15 feet above the sea, a few small angular 

 fragments of volcanic rocks. These fragments would appear to indicate the vicinity of the parent i 

 further in from the reef-flat. 



