t) 



36 P. T. CLEVE, 



Si 59,24 Al 18,16 Fe 3,26 Fe 3,56; Ca 6,31 Mg 2,84 Na 4,00 K 1,31 ignition 0,87 

 Sum. 99,55. 



2. Diorite from Beef-Island Sp. Gr. 2,860 contains 1,27 percent magnetic iron. Ana- 

 lysis by P. T. Cleve. 



Si 61,35 Al 15,39 Fe 4,41 Fe 3,40 Ca 6,60 Mg 3,32 Na 3,87 K 0,95 H 0,58. Sum. 99,87. 



3. Diorite from Ginger Id. Analysis by P. T. Cleve. The rock is more fine 

 grained and darker coloured than 1 and 2 and occurs in strata imbedded in unstratified 

 diorite. It may be termed stratified diorite. 



Si 53,85 Al 17,15 Fe 4,08 Fe 6,95 Ca 8,99 Mg 5,29 Na 3,oi K 0,24 H 0,58. Sum. 100,14. 



4. Diorite from S:t Martin near the town of Philipsburg, eruptive and light-coloured 

 Sp. Gr. 2.72. Analysis by P. T. Cleve. 



Si 65,61 Al 17,26 Fe 2,47 Ca 7,66 Mg 2,50 Na 4,19 K 1,09. Sum. 100,78. 



One may conclude from the small quantity of silica that the rock contains no quartz, 

 and from the little quantity of potash that orthoklase does not enter in the composition. 



The diorite is in inöst places unstratified and in some cases I have distinctly seen 

 that the rock has been injected in a liquid state into branching veins in the surrounding 

 rock. Very fine specimens of diorite occurring in this manner, are exhibited at Brown's 

 Bay in S:t John, also at S:t Martin in the seacliffs near Philipsburg. In other spöts no 

 traces whatever are to be found of a violent intrusion into the surrounding rocks at their 

 contact with the diorite. Thus in several of the small islands south of Sir Fr. Drake's 

 Channel one may find diorite alternating in regular strata with amphibolitic schists and 

 also gradual passages from those schists to massive diorite without any traces of stratifi- 

 cation. It will not be easy to account for these differences as the diorite evidently be- 

 longs to the sarne mäss. I think that the contradiction may be explained by supposing 

 that the diorite is only a strongly metamorphosed clay slate and that the heat has given 

 rise to the change and been increased also, through the same metamorphic action and in 

 some parts of the mäss even been strong enough with the aid of water and a powerful 

 pressure to reduce the rock to a molten state. The gradual passages from diorite to 

 amphibolitic schists and from them to clayslate make the hypothesis very probable. and 

 the heat necessary to melt the rock with the aid of water and pressure, 'need not neces- 

 sarify have been very high. It is also of interest to remark the fact, that the stratified 

 rocks on both sides of the strait between S:t John and Tortola, where the mäss of diorite 

 is not very thick, dip in an opposite direction to the axis of the strait, when at some di- 

 stance north and south of Sir Francis Drake's Channel, where the diorite has evidently 

 been of an enormous thickness, the strata dip to the south as well in Tortola as in the 

 small Virgin-Islands. The strata of the latter islands may be regarded as the continua- 

 tion of the stratified rocks on the northern part of S:t Thomas and S:t John, where the 

 dip is to the north. The change of dip is probably due to an inerease in the volume of 

 the rock by its change to diorite. 



I believe, consequently, that the diorite-mass is a volcanic hearth in fossil state, and 

 I cannot participate in the common spinion, that the volcanic rocks are emanations from 



