40 P. T. CL EVE, 



16. Magnetic-lron-sand occurs in a small quantity on Beef-Island near Tortola, 

 wliere it has been washed down from the anorthite-diorite. 



17. Felsitic breccia. Of that rock I have already treated in the artide on Felsite. 



18. Bluebeache, a rock thus named by the inhabitants, is a kind of felsitic trap 

 conglomerate or breccia, varying very much in appearance. It has generally a dark bluish 

 or greenish colour, sometiraes also brown. It consists of angular pieces of felsite, por- 

 phyry, rounded scorise etc, of various sizes, imbedded in a darkgreen mäss and occasio- 

 nally containing hornblend or chlorite. Often its structure of conglomerate is so oblite- 

 rated, that one may consider the rock to be a kind of trap or porphyry. In fine-grained 

 varieties of this sort, the rock often has a fine spheroidal-structure. Sometimes the horn- 

 blend increases to such a degree that the rock may be mistaken for diorite. It is very 

 likely that the clay-slate of the Virgin-Islands is bnly an exceedingly fine-grained variety 

 of bluebeache. 



Near Virgin-Gorda, in the small island of Prickly Pear occurs a remarkable variety 

 in the form of an argillaceous, bluish-gray very fine-grained mäss. 



The bluebeache belongs to the cretaceous formation of the Virgin-Islands, S:te Croix 

 and Puerto Rico. 



19. Porphyritic-breccia, conglomerate and tufa, very much resembling bluebeache, are 

 igneo-sedimentary rocks of the eocene formation of S:t Bartholomew and S:t Martin. The 

 rock, varying in an extraordinary degree, is very difficult to describe or characterize. It 

 is often stratified and alternates in S:t Bartholomew with strata of fossiliferous limestone. 

 It is composed of larger and smaller fragments of different kinds of rocks, as volcanic 

 scorite, small pieces of an altered rock, probably clay-slate, and of porphyry, etc. In dif- 

 ferent places the rock is more or less coarse or fine-grained, sometimes resembling clay- 

 stone or clay-slate of a light colour. 



The more fine-grained varieties frequently contain smaller crystals of feldspar, and 

 are thus a kind of porphyry. It has sometimes a fine variolitie structure. 



It contains very often fossils or nodules of fossiliferous limestone which proves it 

 to be evidently of submarine origine. 



By metamorphosis the rock is sometimes much altered. Thus chert-breccia and 

 quartzite occur in S:t Bartholomew which have obviously been breccia in former times. 



20. Trachytic tu/as, composed of small quantities of feldspathic and often pumiceous 

 ashes, occur in the volcanic islands, as in Saba, S:t Eustatius, S:t Kitts, etc. 



VI. Notes on the geology of the other West-India Islands. 



Cuba. The geology of this large island is very little known. In the history of 

 Cuba by Ramon de la Sagra a chapter is devoted to the geology of the island*). The 

 greatest part of the island is covered by a large and thick limestone formation, which, 

 to judge froin the fossils, seems to be of the same geological age as the limestone of Ja- 

 maica, S:t Domingo and Puerto Rico etc, or the iniocene age. The fossils, of which 



*) Histoire physique, politique et naturelie de 1'ile de Cuba T. I. p. 107 Paris 1842. 



