6 P. T. CLEVE, 



manganese. At the southern point of Water Island the felsite rests upon bluebeache. In 

 sorae parts of the island diabase occurs. Thus the felsite at Red Point is traversed by a 

 dike of diabase of spheroidal structure. Near Coki Point the bluebeache is penetrated by 

 a dike of augitic-porphyry, a black fine-grained rock with crystals of augite. 



The whole surface of the island is covered by a quantity of angular stones, large 

 boulders or a rnore fine-grained detrital mäss, formed by alteration of the surface-rock. 

 In those newer beds occur several shells of still living species of terrestrial inollusca and 

 also shells of an extinct species, the Helix incerta Fér, closely related to the Helix nota- 

 bilis Sh. living in Tortola. 



A recent clay deposit of marine origin occurs on the north side, near Buck's Bay. 

 It is a plain overgrown by Coccoloba, Cocos, etc, and scattered över the surface occur many 

 shells of still living species. I found on the spöt Ostrea Fröns Lin, Cardium muricatum 

 Lin, Donax denticulatus Lin, Mytilus txustns Lin, Area umbonata Lamk, A. lactea Lin. Murex 

 brevifrons Lamk and Oliva reticularis Lk. 



2. Smaller islands around S:t Thomas. S:t Thomas is surrounded by several small 

 islets. To the west lies Cabrita or Savana Island, which I have been very near. It seems 

 to be a bluebeache rock. Little Saba south of S:t Thomas is believed to have been a vol- 

 cano, but this is not correct, the rock being of the same kind as at Red Point, or a fine- 

 grained felsite, sometimes altered to kaolin. Flat Cay, between Saba and S:t Thomas, is 

 a small rock of a coarse felsitic breccia. Water Island consists of a compact yellowish- 

 brown felsite mixed with spöts of quartz. At the southern bluff the felsite rests upon 

 bluebeache. Buck's Island is a low island, south of S:t Thomas. The rock is a light co- 

 loured diorite reseinbling syenitc and penetrated by numerous dikes of diabase or granu- 

 lar granite. 



The diorite is composed of triclinic feldspar, black hornblend and sorne green tale 

 or mica. It contains nodules of epidote. The rock is massive and has a distinct sphe- 

 roidal structure. The diabase is black and fine-grained and sometimes contains crystals of 

 augite or nodules of compact epidote. The granular granite is a mixture of feldspar (oligo- 

 klase), glassy quartz in pyramides, and hexagonal leaves of greenish mica or tala In one 

 spöt I have seen the granite intersecting dikes of diabase. 



Sketch of Bucks Island from E. S. E. Diabasdikes intersectinp; diorite. 



S:t James Island seems to consist of bluebeache and felsitic breccia, penetrated by 

 very altered trap-like rocks. I have only visited Little S:t James Island. 



North of S:t Thomas, and, connecting the Tutu Bay Point with Whisling Cay and 

 Marys Point in S:t Johns, is a band of long and narrow islets: Thachts Cay, Grass Cay, 

 Singo Cay, Levango Cay and Congo Cay. 



They consist of more or less altered clay-slate or flagstones, which are stratified, 

 striking E — W and dipping 70° to the north. Congo Cay north of Lovango-Cay is a ridge 



