550 proceedings oe the geoiogical society. [June 25, 



The Island of St. Bartholomew, situated in 62° 51' 6" W. long, and 

 17° 53' 50" N. lat., is a narrow island, about 10 kilometres in length. 

 It is mountainous ; and the soil is very stony, rock-fragments and 

 boulders existing everywhere, and proving the great denudation 

 which has gone on for ages. 



The rocks consist of: — a fine-grained claystone, which has been 

 tilted up by a syenite porphyry ; of an immense depth of igneo- 

 sedimentary rocks, consisting of tufas and breccias ; of conglome- 

 rates, which include portions of the breccias ; and of limestones, 

 which are covered by and rest upon members of the igneo-sedi- 

 mentary series. 



The limestone is a very hard and compact rock, with a fiat even 

 cleavage. It has a decided tendency to break in parallelopipedal or 

 cubic pieces ; and the fissures generally contain fine crystals of calc- 

 spar. Usually the fossils included are badly preserved. 



Resting on unfossiliferous conglomerates, breccias, volcanic tufas, 

 and scoriae, and being covered by similar beds, there is no strati- 

 graphical guide to the age of the limestones. They dip at no very 

 great angle, and have suffered great denudation in some places, and 

 much chemical change universally. 



Near the contact of the conglomerates and limestones, rounded 

 concretions of grey limestone, with fossils, are found. 



All the Madreporaria which were collected and sent to me are 

 heavy, usually well preserved, and dark grey in colour. In their as- 

 pect they resemble Silurian fossils ; and in mineral condition they are 

 totally unlike those found in any of the Miocene formations of the 

 "West Indies. 



The corals consist of a carbonate of lime which has replaced the 

 original hard tissue and infiltrated into the interstices, where it is 

 iisually crystalline. Sometimes the outsides of the fossils consist of 

 granular or amorphous carbonate of lime, and the insides are crys- 

 talline. In other specimens even the linear septa have been replaced 

 by minute dark crystals. 



The specimens include simple or solitary forms, and true reef- 

 building types. 



The latter are large, and parts of them are well preserved. 

 No Miocene deposits exist on the island ; and the so-called Pliocene 

 is absent. 



The limestones and the concretionary rock contain both of the 

 types of coral (simple and compound) ; and whilst the branching 

 forms give evidence of having been broken off with violence, and of 

 having been rolled, the simple forms are usually very perfect. 



The fossiliferous deposits appear therefore to have collected out- 

 side a reef, and in moderately deep water — the floor of the sea 

 having been the natural habitat of the numerous simple corals, 

 and having also been the area for the accumulation of volcanic 

 ejectamenta. 



