ON THE GEOLOGY OF THE NORTH-EASTERN WEST-INDIA ISLANDS. 9 



the rocks is east to west and the dip is almost vertical or sornewhat to the south. Near 

 the Seacow Bay are found some small veins of coppcr-ore. Near Coxheat occurs a fine- 

 grained black clay-slafe of the same kind as the slate in S:t Thomas. The south-western 

 part of Tortola consists of a ridge of härd crystaline limestone, sometimes containing brown 

 garnets. The rock does not conlain fossils and continues through the hill near Coxheat. 

 At the shore below Coxheat, according to Mr Schomburgk, diorite is found. North of the 

 limestone-ridge of the west-end are stratified flagstones with garnet, epidote and specular 

 iron. Near Belmont the strata are penetrated by veins of quartz or pegmatite granite. At 

 that place the strike of the strata is E — W. and the dip about 45° to the south. West 

 of Cappoon Bay a dike of diorite is visible; it has a direction from N — S., and east of 

 the same place are dark stratified rocks containing scoriaä and graduating into bluebeache. 

 The latter have the strike E. N. E. — W. S. W. and dip 70° to the south. The bluebeache 

 extends över the centre of the island and has the same appearance as in S:t Thomas. It 

 is often intersected by large veins of quartz, coloured by iron, and sometimes containing 

 smaller larnmge of black specular iron. Such a vein extends across the bay between Buck's 

 Island and Beef Island, another is visible near Road Town. It is not improbable that gold 

 may be found in these veins. I have not visited the north side of the island, except th 

 coast opposite to GuanaTsland. At this place the rock is felsitic. 



e 



6. Smaller islands around Tortola. Sandy Cay is a small rock between Tortola and 

 Iost van Dyck. Most of the island- is covered with shell-and coral-sand. The rock is a 

 dark, trap-like mäss, not stratified, with crystals of hornblend and quartz in veins or no- 

 dules. It has a parallelopipedic structure and seems to me either a variety of the rock 

 near Cappoon Bay in Tortola, or diabase. 



Iost van Dyck is a tolerably large island, 326 meters in hight. I have only visited 

 the middle part of the southern coast, where I found bluebeache-conglomerate. 



Great Tobago, west of Iost van Dyck, is a small island, the northern part of which 

 is composed of a kind of dark felsitic conglomerate, and in the southern parts there are 

 stratified flagstones striking E — W. and dipping 70° southwards. 



Little Tobago, between Great Tabago and Hans Lollik, is a rounded rock, very bard 

 and not stratified. Its colour is dark and it may be perhaps a continuation of the diabase- 

 mass of Hans Lollik. 



Great Thacht Island near the west end of Tortola is a high ridge and a continua- 

 tion of the strata of the latter island. The middle of the island is a continuation of the 

 crystaline limestone of Tortola. The rock is very härd, does not contain fossils, and has 

 a distinct parallelopipedic structure. North of the limestone-rock are almost vertical me- 

 tamorphic strata. On the small proinontory opposite to Mary's Point also occur stratified 

 flagstones, penetrated by a vein of pegmatite. 



Little Thacht Cay, near the west end of Tortola, is a stratified and garnetiferous si- 

 licious limestone-rock. Its strike is E — W. and dip southerly. 



Frenchman Cay has about the same geological structure as Little Thach Cay. The 

 strata strike E. N. E — W. 8. W. and dip to the south. 



K. Vet. Akad. Handl. B. H. St:o 12 * 



