24 J- SCHETELIG. M.-N. Kl. 



The microscopic examination of the slice of the amphiboHte analysed 

 from Scotts Nunataks has given the following results: — 



Apatite is rather abundant. 



Iron-ore (magnetite and pyrite) is met with in large amounts. Often 

 irregular grains of pyrite are shown bordered with magnetite. Both pyrite 

 and magnetite are partly altered into haematite. 



Titanite is shown unequally distributed in comparatively large grains, 

 of irregular outline. 



Biotite is abundant. The absorption || ß and ;' is not so strong as 

 in the biotite in the granite and granite-pegmatite; ß and ;' brown, a 

 straw yellow. In the slice the biotite happens to be in excess over the 

 amphibole, but judging from the macroscopic examination of the rock- 

 specimen the amphibole seems to prevail over biotite. In agreement with 

 this the content of amphibole calculated is still greater than the corresponding 

 content of biotite. 



Muscovite is only present in traces. 



Amphibole is a common green hornblende with abs. y '^ ß '^ a . a 

 light yellow, ß light brownish green, and y deeper bluish green. In 

 sections -l ß the angle c y = 20° — 22°. 



Plagioclase the prominent mineral in the rock, shows zonal structure. 

 According to determinations of the extinction a in sections -i- the 

 axis a, the external zone is labradorite, An.r,^; in the middle zones the 

 content of anorthite rises from An,io to An7r, . In the central nucleus 

 ("Kerngerüste") the content of anorthite reaches the maximum-value of 

 Angg. I have for an average-value calculated the plagioclase as bytownite 

 An75 (Abi Aug). The central nuclei ("Kerngerüste") which consist of 

 anorthite, are usually small and irregular, probably due to resorption. As 

 mentioned above the plagioclase shows intergrowth with quartz. 



The quartz is unequally distributed, allways crushed and with undulatory 

 extinction. The larger grains are possibly of secondary origin. 



Gneiss. The gneiss-specimens from Scott's Nunataks are dark gray, 

 fine-grained rocks with well marked schistosity, showing abundant biotite in 

 the schistose-planes. The gneiss-specimens include two definite types of 

 rocks, but with no visible difference in external appearance. One group is 

 derived from granitic rocks showing quartz, microcline, plagioclase (oligo- 

 clase-andcsine An:^o) and biotite as the chief constituents. Biotite is abundant 

 and arranged in parallel bands, frequently including zircons surrounded by 

 pleochroic halos. Magnetite and apatite occur sparingly. The quartz is 



