PKNTTI FSKOI.A. M.-N. Kl. 



'l'lic s.implc was till rclorc \(fv piiic aiul llic dcviatiDn i'vom the garnit 

 ratio is piobaljlv solch' (lur Id the iioii-diicrininalion of fr-rrir iron. 



Plagioclasc is somewhat more abundant than the hornblende and .shows, 

 in sections J_ PM, extinc^tion angles of 24', corresponding to the com- 

 position Ab_^r,. 



The hornblende is brownish green, of the eonimon character, with 

 comparatively faint pleochroism and large axial angle, [i = 1.660 + 0.003, 

 corresponding to about r i per cent FeO and 1 4 MgO. 



Apatite is abundant, and occasionally there occur flakes of biotite 

 penetrating all the other minerals. 



This rock has clearly a primary consolidation structure, appearing 

 especially in the fact that the plagioclasc is idiomorphic in its relation 

 to the hornblende. 



As to the conditions of the existence of garnet in this rock we refer 

 to what will be said below, in the discussion of the garnet-bearing norite. 



Garnet-Amphibolite from Arøen, Kragerø. 



The garnet-amphibolite from Aroen, Kragero, is a medium-grained 

 hornblcnde-plagioclasc-rock containing frequent large crystals of red garnet, 

 almost filled up with inclusions of quartz. This garnet showed 



"d = 1-7917 



corresponding to the composition Fe53Mg3-Ca._,4. Even if the proportion of 

 lime differs from this calculated value, the main character of this garnet 

 is at any rate the same as in all the other amphibolite-garnets, with pre- 

 ponderating almandite-compound. 



Norite from the vicinity of Tvedestrand. 



The specimen investigated was derived from an erratic boulder found 

 in Giving, Dybvåg. It is a medium-grained rock where the feldspar grains 

 are tabular on M (ophitic structure) and arranged parallel to one another. 

 Some pyrrhotite is visible to the unaided eye, and sparing!}- garnet. 

 Of the latter mineral there was, in the specimen, but one large crystal 

 (2 cm in diameter) and a few smaller. These crystals are almost free 

 from inclusions, so that the sample for analysis prepared from the 

 large crystal, was practically clean. The result of my analysis is the 

 following : 



