Vol. 50.] BASIC ERUPTIVE ROCKS OE GRAN. 33 



magma only slightly different from the before-mentioned average- 

 magma, which, for the sake of brevity, I will designate as magma U. 1 



If the averago composition of the rocks of Brandberget is, 

 possibly, a little more basic than the average composition of the 

 bosses between Brandberget and Dignaos taken altogether — that is. is 

 more basic than magma — this is certainly not the case with the 

 boss of Solvsberget. The rocks of Solvsberget on the whole 

 undoubtedly possess an average composition conforming very 

 closely to that of magma 0. Besides, we have found that the bulk 

 of the eruptive rocks on Solvsberget is represented by an olivine- 

 gabbro-diabase of nearly the average composition. Nevertheless 

 I have also observed on Solvsberget a series of differentiations of 

 magma 0, which are, on many accounts, of much interest. 



Moreover, on Solvsberget I have found the same pyroxenites as 

 on Brandberget, although to a more limited extent, namely on the 

 western and south-western side of tho hill, as contact-facies ; but 

 I have not observed any hornblendite. 



On the eastern end of the boomerang-shaped boss, where the 

 tectonic relations have been quite exceptional, a peculiar differen- 

 tiation has taken place. By this differentiation along the contact 

 there is separated out a magma which has consolidated as labrador- 

 porphyrite. 



The chemical composition of this labrador-porphyrite has not 

 yet been determined by analysis, but it is assuredly not very 

 different from that of the labrador-porphyrite of Huken, north of 

 Christiania, where this rock is spread as an old sunken lava- 

 flow over large areas. An analysis of the Huken rock, made in the 

 laboratory of Herr L. Schmelck, gave : 



SiO., ... 47-50 



Ti0 2 302 



A1.,0 3 1757 



F&A, 7-24 



PeO 508 



MgO 3-31 



CaO 619 



Na o 3-00 



K.,0 328 



H:,0 1-70 



Ca0O 3 0-tiS 



Ca 3 P 2 O s 100 



10017 



The difference between this and magma 0, as will be seen, is 

 quite unimportant, because the composition for most compounds 

 lies between magma and the composition of the olivine-gabbro- 

 diabase from Dignaes. However, a slight differentiation has 

 taken place, the mixture of the labrador-porphyrite being poorer 



1 As above mentioned, the average composition of the rocks of Brandberget 

 seems to be a little more basic than the average of the more southern 

 occurrences. 



Q. J. G. S. No. 197. d 



