38 P. T. CLETE, 



Fe 6,30 4,34 5,84 5,21 6,50 



Ca 7,36 9,83 7,63 12,31 6,68 



Mg 6,16 5,35 3,41 3,93 4,03 



Na 4,11 3,98 4,00 3,24 4,51 



K 1,09 0,55 0,90 — 0,20 



H 3,63 2,68 1,35 2,05 1,62 



Sum. 99,37 99,43 99,26 100,06 99,72 



9. Labrador-Porphyry, in chemical composition closely related to the diabase, is in 

 the West-Indies such a distinct kind of rock that I may treat of it here as a separate 

 species. It is found only on Culebra, which island seeins to be entirely formed of that 

 rock. The Labrador-porphyry is a dark-brown or grayish black and fine-grained rock, 

 and contains numerous whitish crystals of feldspar, which, judging from the chemical com- 

 position of the rock, are labrador. Those crystals are commonly arranged in star-like 

 groups or crossing one another. Also occur in the mäss small needles of green augite. 



The Sp. Gr. of the rock is 2,87, and the chemical composition, according to an ana- 

 lysis by Dr. Th. Nordström, the following: 



Si 52,55; Äl 14,96; Fe 5,80; Fe 6,19; Ca 7,05; Mg 3,22; Na 5,37; K 2,83; ignition 2,48. 

 Sum. 100,45. 



The Labrador-porphyry is a massive rock, in general with a nne parallelopipedic or 

 polygonal structure. It encloses numerous veins with rock-crystals, red iron-silex, green 

 quartz or calcarious spar, sometimes, also, epidote or a chlorite-like mineral. 



10. Anorthite-Diorite, is a crystaline mixture of anorthite (analysis of that mineral 

 is given above), hornblend, and titaniferous magnetic iron. The rock is seen only in 

 Beef-Island and occurs perhaps also in Virgin-Gorda. In the former island it form a mäss 

 enclosed in diorite. 



Its Sp. Gr. is 3,059. and the composition according to an analysis by Mr. Patr. 

 Peterson: 



Si 44,60; Äl 15,28; Fe 8,50; Fe 8,03; Ca 14,50; Mg 6,82; Na 0,33; K 0,oi; Ti 0,92; H 0,56. 

 Sum. 99,65. 



With the magnet I was able to extract 7,5 percent of magnetic iron. 



The anorthite is grayish white, half-transparent and sometimes it shows a fine twin- 

 striation. 



The hornblend forms black, shining crystals, sometimes of a large size. The mag- 

 netic iron occurs in small grains penetrating the rock. 



The anorthite-diorite has a polyhedric.or spheric structure and contains veins with 

 quartz or pegmatite-granite. 



As accessorial minerals in the rock I have found epidote and some traces of copper- 

 minerals. 



11. Trachyte is the ruling rock in the volcanic islands as Saba, S:t Eustatius, S:t 

 Kitts, Montserrat etc. The rock of Saba is composed of a dirty-red porous mäss in which 



