ON THE GEOLOGY OF THE XORTH-EASTERN WEST-INDIA ISLANDS. 33 



3. Coal of miocene date is said to occur in Puerto Rico and in Anguilla. 



4. Granite occurs in two different forms in the cretaceous formation of the Virgin- 

 Islands, viz: Penmatite or granite occurring in veins and Granular granite occurring in dikes 

 and probably of eruptive origin. 



The peymatite is always eoarse and crystaline, composed of quartz, white oligoklase, 

 reddish orthoklase and very little mica. It contains occasionally epidote, hornblend, preh- 

 nite and magnetic iron. This variety is found in veins in the anorthite-diorite of Beef- 

 Island, at Belmont (Tortola) and in Great Thacht-Island. 



Granular granite is a more or less fine-grained mixture of quartz, feldspar (oligo- 

 klase preponderating) and mica. The quartz is glassy, half transparent and commonly cry- 

 stalized into pyramids, the feldspar occurs in rather small grains, often distinctly striated 

 and of a Avhitish-gray or reddish colour. The mica is black or green and occurs in hexa- 

 gonal leaves or needles. It is sometimes replaced by talc. It seems to graduate into fel- 

 site and always occurs in dikes. This rock occurs on BuckVIsland (near S:t Thomas) in 

 dikes intersecting the diorite, and in the small Virgin-Islands as Peter's Island, Salt-Island 

 and Cooper's Island, also intersecting the stratified metamorphic ro^ks. The small cays bet- 

 ween Tortola and Virgin Gorda, George Dog etc. seem to consist of the same kind of rock or 

 perhaps a crystaline variety of felsite. The rock in the cay of George's Dog consists of 

 a mixture of reddish and whitish feldspar, some quartz, very little mica and greenish 

 hornblend. 



Granular granite from Buck's Island has the sp. gr. 2.72 and contains according to 

 an analysis by Dr. Th. Nordström. 



Si 64.71; Äl 15,09; Fe 2,56; Ca 4,51; Mg 1,16; K 1,38; Na 5,29 H 4,86. Sum. 99,56. 

 The rock from George's Dog sp. gr. 2,701 contains, according to an analysis by P. 

 T. Cleve. 



Si 71,60; Äl 13,63; Fe 3,03; Ca 3,37; Mg 0,9 i; Na 4,54; K 1,31 Ignition 0,63. Sum. 99,04. 



The great quantities of lime and sodium indicate that a kind of oligoklase is here the 

 preponderating feldspar. 



5. Felsite, a mixture of feldspar and quartz, of which component parts the propor- 

 tions are highly variable in different specimens, as is easily seen from the following 

 analyses. 



I. Felsite from »Adlers villan S:te Croix, somewhat altered, coinpact, in small pieces 

 half translucent. Sp. Gr. 2,702. Analysis by P. T. Cleve. 



II. Felsite from Red-Point (S:t Thomas). Dirty white, compact with small round 

 spöts of quartz. The structure of the rock is basaltic. Sp. Gr. 2,64. Analysis by P. T. 

 Cleve. 



III. Felsite from the »Sound» (Virgin Gorda). Gray, micro-c^staline, with a small 

 quantity of hornblend. Sp. Gr. 2.69. Analysis by Dr. Th. Nordström. 



IV. Felsite from Regis Point (S:t Thomas). Brownish gray, compact, and with small 

 scattered reddish döts. Sp. Gr. 2,637. Analysis by P. T. Cleve. 



K. Vet. Akad. Handl. B. 9. K:o 11. 5 



