ON THE GEOLOGY OF THE NORTH-EASTERN WEST-INDIA ISLANDS. 11 



diorite contains a large number of veins with the general direction from N — S. They 

 are filled with white, sometimes crystaline quartz, sometimes with carbonate of iron and 

 contain native coppur, and gray, red, yellow or green copper-ore and molybdena. They 

 have formerly been worked in the soutb-eastern corner of the islancl, where there are 

 some smaller mines. 



North of the diorite is a mäss of quartzite, very härd, dirty coloured, fine-grained 

 and broken on the surface in angular pieces. It seems to have been a kind of sandstone, 

 but no stråt ifieation is visible. Near Plum Bay I have found a small mäss of a dark 

 trap-like rock, probably anorthite-diorite. Along the coasts af Long Bay are gray felsitic 

 rocks, containing some hornblend. The rocks on the shores at the Sound are also felsite. 

 In the latter place the rock has a yellowish-gray colour and a distinct parallelopipedic 

 structure; it is very härd and crystaline and contains a little hornblend. 



8. Smaller islands around Virgin Gorda. North of Virgin Gorda are three smaller 

 islands Necker Island, Prickly Pear, and Mosquito Island. In the west end of Necker Is- 

 land are very altered porpoyritic rocks and in the east end occur strata of tufflike conglo- 

 merates and breccia. The strata strike N. W. — S. E. and dip abont 30° S. W. In the 

 southern part of the island are large quantities of coral-and shell-sand, overgrown by 

 Coccoloba, Cactus etc. Prickly pear. In this island the rock is a kind of greenish clay- 

 stone, without distinct stratification and probably a variety of Bluebeache. I did not land 

 at Mosquito Island, but I passed very close by it and to judge from the dark-green colour 

 of the seacliffs the rock seems to be bluebeache. The small islets of »Saeldog» seem also 

 to be bluebeache rocks. 



Between Tortola and Scrub Island there are some smaller cays, the Dog Islands, of 

 which I only visited the George Dog. The latter cay is a rock of granite-like felsite and 

 the others seem to be the same. 



9. Smaller islets between Virgin Gorda and S:t John. In a direction from N. E. to 

 S. W. extend from Virgin Gorda to the south-eastern corner of S:t John a row of islets, 

 separated from Tortola by Sir Francis Drakes Channel. Broken Jerusalem, near Virgin 

 Gorda, is a low flat cay, covered with numberless large boulders, looking at a distance 

 like a town fallen in ruins. The rock is diorite of a spheroidal structure. By alteration 

 the softer parts of the rock have been swept away and the harder, large concretions, left 

 in the form of boulders. 



Round Rock is a conical, barren rock, consisting, in the northern part, of diorite, 

 penetrated by veins of quartz or oligoklase-pegmatite, and by numerous trap-dikes. The 

 diorite contains some small spöts with copper-minerals. The southern part of the cay is 

 composed of stratified rocks, gray or green silicious limestone with red garnets, or amphi- 

 bolitic and feldspathic flagstones. 



Ginger Island. In the middle of the northern shore is a mäss of diorite, which is 

 interstratified by, and gradually passes över into well stratified amphibolitic and feldspathic 

 rocks. The strata strike E. N. E. — W. S. W. and dip 70° to the south. At the points 

 of contact between the diorite and the stratified rock I could not find any traces of a 

 violent intrusion of the diorite. The latter rock contains, on the contrary, fragments of 

 the stratified rocks, which have the same direction as the flagstone. The flagstones are 



