166 Geological Society : — 



off from the sea. In this is a perfectly round hole where soundings 

 of 20 fathoms or more are reported, on the authority of Mr. Arundel, 

 and even deeper ones on that of the captain of a merchant- vessel. 

 On the coral ring there rises a mass of modified trachyte, the subject 

 of the following communication, about 60 feet in height. The 

 great depth of the lagoon and the rock-mass on the ring are not 

 compatible with the origin of the reef by subsidence or outward 

 growth ; and the possible hypothesis is put forth that this reef had 

 grown on the lip of a volcanic crater, or on an island, such as 

 Krakatao, in which the interior has been enlarged and deepened by 

 volcanic explosion. 



2. ' A Phosphatized Trachvte from Clipperton Atoll.' By J. J. 

 H. Teall, Esq., M.A., F.R.S., V.P.G.S. 



Specimens from the projecting rock described in the preceding 

 communication are dark brown, white, or cream-coloured. The 

 brown specimens are trachytes, composed of glassy phenocrysts of 

 sanidine set in a groundmass of microlitic felspars with brown inter- 

 stitial matter. The light-coloured rocks are more or less altered 

 trachytes, in some of which the glassy phenocrysts of sanidine may 

 still be recognized. Analyses of several specimens show that the 

 rocks all contain varying amounts of phosphoric acid, as indicated 

 by the following table : — 



I. II. III. 



per cent. per cent. per cent. 



SiO, 54-0 - 437 2-8 



P.,0 5 84 170 38-5 



Loss on ignition 31 12-3 230 



The last specimen consists of 95 per cent, of hydrated phosphate 

 of alumina, with some iron, having thus a composition allied to the 

 so-called redonite from Eedonda in the West Indies. The progressive 

 alteration affects first the groundmass, then the microlitic felspars, 

 and lastly the poruhyritic crystals of sanidine ; and it is probable that 

 the change has been effected by solutions of alkaline phosphate and 

 other compounds derived from the droppings of sea-birds. A some- 

 what similar phosphate, shipped from Connetable Island off French 

 Guiana, is referred to on the authority of Mr. Player. 



3. ' The Pliocene Deposits of the East of England.— Part I. The 

 Lenham Beds and the Coralline Crag.' By F. W. Harmer, Esq., 

 F.G.S. 



From the discussion of lists of fossils, a large number of sections, 

 and a series of borings, the author endeavours to establish the 

 following propositions : — 



I. With regard to the Lenham Beds : — 



(«) That they are older than the Coralline Crag, thirteen out of 

 sixty-seven mollusca found in them being characteristic Miocene or 

 Italian Lower Pliocene forms unknown or very rare in the latter 

 formation. 



(o) These beds had probably been upheaved, consolidated, and 

 exposed to denudation before the deposition of the Coralline Crag, 



