1921. No. 8. 



ON THE ECLOGITES OF .\<^R\VA\-. 



Veined gneiss from Blaatjtld, K lei ven at Gei ranger, 

 Son dm o re. The rock, as a whole, is rather leucocratic and of a beautiful 

 light red colour. The lighter as well as the darker, biotite-bearing, bands 

 are very thin, but there is no parallel arrangement of any of the con- 

 stituents, nor any mechanical deformation. The constituents are microcline, 

 quartz, oligoclase, biotite, muscovite, magnetite (as octahedral 

 and orthite as megascopic grains. Both perthite and antiperthite occur, 

 and plagioclase-quartz-myrmekite is abundant. 



Almandite-gneiss from Grytingen, Selje, occurring as a 

 homogeneous band a few meters thick. This rock contains much quartz 

 and, as the second in quantity, 







o o 



" o o' 



I m 



Fig. 3. Augengneiss, passing over into 

 "veined gneiss", with dikes of aplite (dotted). 



oligoclase. Dark brown biotite 

 and an optically uniaxial colourless 

 m i c a are almost equal in amount. 

 The biotite contains minute zircons 

 with pleochroic halos. Large prisms 

 of apatite and still larger crystals 

 of almandite, almost free from in- 

 clusions, complete the list of minerals. 

 Potash felspar is absent. 



Oligoclasite from Bleie- 

 skars\'and. Syv de, Sen dm ere. 

 In this connection may be mentioned 

 a rock showing some approximation 

 towards the labradorite-rocks, though 

 perhaps more closely related to the 

 gneiss. The specimen studied has 



been collected by H. Reusch, and I do not know its mode of occurrence. 

 It is chiefly composed of plagioclase, in sections J_ PM showing 

 extinction angles of + 9"^ corresponding to the composition Ab-.,. Quartz 

 occurs only as minute rounded inclusions, and potash feldspar as anti- 

 perthitic particles. Other minor constituents are biotite, apatite and 

 chlorite. The structure is non-foliated. 



Such an oligoclasite might well be supposed to have originated as a 

 band by the differentiation by crystallization under stre-ss. True labradorite- 

 rocks often occur in the same manner as bands in the gneiss, and appear 

 to have cr3'stallized later than the darker schliers of the mixed country- 

 rock. Such is an occurrence on Aasnaesn akken near Bryggen, 

 Nordfjord. The light band is a few meters thick, and is composed of 

 a plagioclase with 60 pt Ab, besides hornblende, biotite and abundant epidote. 

 In spite of resemblance in the mode of occurrence, it is difficult to understand 

 this and other similar rocks as direct differentiates from the gneiss in the 

 above manner, as their composition shows such a strange and persistent 

 character. 



Vid.-Selsk. Skrifter. I. M.-N. Kl. 1921. No. 8. 



