205 



a last product of crystallization, the whole mass of rock being 

 densely penetrated by calcite. The biotite is interesting because 

 it shows, especially in large individuals, a marginal zone of the 

 usual brown colour, while the core is very light, almost colour- 

 less. The felspar seldom shows twin formation, but often a zonal 

 extinction; the borders, too, often consist of fresher substance 

 than the middle zone. Of the rocks I have seen this one 

 reminds me most of some forms of bostonite, but I presume 

 that its constitution is more basic. 



d. Dike rocks of nepJieline-tephritic type. Besides the al- 

 ready described lenticular or boss-shaped rocky mass with its 

 various types, and the red or grey porphyry dikes that belong 

 to the same, the sedimentary rock at C. Fletcher is interspersed 

 with some darker dikes of a different appearance, and of which 

 one proved to consist of ordinary basalt and is therefore men- 

 tioned among the basalt rocks. Two other, fairly narrow dikes, 

 belong, on the other hand, to another and interesting type, 

 which is described herewith ^). 



Two of the specimens, in spite of their macroscopically 

 divergent appearance, form such an obvious transition to the 

 one last described that they ought certainly to be classed with 

 it. We find, porphyritically, now biotite partly discoloured 

 and bleached, and rich in inclusions of regularly arranged fine 

 needles, now light pseudomorphs, entirely transformed into 

 serpentine and carbonate, from a mineral which I hesitatingly 

 hold to have been amphibole. In addition there are areas that 

 can very well have been composed of olivine. True felspar 

 phenocrysts seems to be lacking. The ground-mass consists chiefly 

 of lath-shaped, strongly altered felspar, while it is interwoven 

 with a carbonate mass; ore (titanic iron ore?), apatite, and fine 

 micaceous scales also occur. To what extent a pyroxene or am- 



*) The samples examined are, it is true, not taken from the dikes in situ, 

 but were found in such a position that their origin from them can 

 scarcely be called in question. 



