ON THE GEOLOGY OF THE NORTH-EASTEEN WEST-INDIA ISLANDS. 



25 



tholomew dip to the south. It seems to me very probable that the change of the dip in 

 that place is occasioned by the eruption of the porphyry. 



L'ans de S:t Jean. S:t Jean. The fort of Gustavia. 





a Syenite porphyry. b conglomerate. c variolithe. d claystone. 



The igneo-sedinientary strata of tufas and breccias alternate with beds of the fossili- 

 ferous limestone. They generally strike E — W. and dip to the south 20°. That system 

 of rocks has been subjected to a powerful denudation, through which it has been divided 

 by nurnerous vallies, so that now only fragments in form of conical hills remain. For 

 that reason it is very difficult to decide which of those spöts of limestone originally formed 

 continuous strata. 



« -^ . 



L'anse 







Ö 03 



£ S 



bc^ 



publique. 



Claystone. 



CO o 



o ■- 



.2 g 



P bD 



w § 



L'anse g 



des cailles. ^ 



Section across S:t Bartholomew. 



The conglomerates and breccias occur in numberless varieties. Some of them have 

 a great resemblance with the bluebeache of the Virgin-Islands, and contain angular or 

 rounded pieces of porphyritic rocks, alveolary scorise, and smaller pieces of a rock resem- 

 bling slate. All these fragments are mixed together to a more or less coarse conglomerate, 

 which has often uudergone strong alteration. 



Near the contact with the limestone-beds are often found rounded concretions of 

 gray limestone with fossils. In some parts of the island as in the west end and near 

 L'Orient the conglomerate is not so coarse and is composed of small angular pieces of 

 various colours. A very fine-grained, almost sandy, variety, resembling puzzuolana and of 

 a dark brown colour, is found near LOrient. Another variety of distinct variolitic struc- 

 ture occurs in strata of about 1 metre in thickness in the hills between S:t Jean and the 

 Fort of Gustavia. The latter variety contains a greenish granular mäss, and round con- 

 cretions of a lighter colour. The very finegrained conglomerate can scarcely be distin- 

 guished from a lighter coloured clayslate. This variety, which may be termed claystone, 

 is found in many places in the island and generally caps the hills. In some places the 

 claystone contains smaller crystals of feldspar and there it graduates into a kind of stra- 

 tified porphyry. In the valley between Grand-fond and the eastern coast of the island 

 occur a great number of interesting varieties of breccias and conglomerates. They have 



K. Vet. Akad. Handl. B. B. N:o 12- 



