1915- ^O- 4- REPORT 0.\ ROCK-SPECIMENS. 1 7 



According to the microscopical examination I should think that the 

 conclusion is permissible, that the ordinary granites from the two localities 

 are identical : 



1. The external appearance of both granites is the same: medium-grained, 

 light-gra\' or reddish-gra\- rocks of strongl}' leucokratic character. 



2. The mineral composition of both granites is the same: potash-felspar 

 (orthoclase or orthoclase parth' altered in microcline or also micro- 

 cline) is the prevailing felspar in the two granites; 



the plagioclase in both granites is determined as oligoclase : 

 Ab4Ani — r- Ab; An^ ; 



biotite shows the same strong absorption in both granites with 

 ß and ;' dark reddish-brown ; pleochroic halos surrounding included 

 minute zircons are found in the biotite from both localities; 



muscovite is alwa3's present, but in variable amounts ; 



apatite is usualh^ found sparingly; 



iron-ore (magnetite and pyritel is always found verv sparingly. 



3. The chemical composition is — according to the analyses — nearly 

 the same. It must be remembered, that the ordinary granite from 

 Mt. Bett\- has not been analysed. 



4. The granites from the two localities are not visibly affected bv stress; 

 they are both seen to be entireh* unsqueezed. 



5. The granite from Mt. Betty as well as the granite from Scott's Xunataks 

 are younger than a complex of gneissic rocks. The specimens collected 

 from both localities show intrusions of the granites into the gneiss-rocks. 



Granite-Pegmatite. The rock-specimens from Scott's Xunataks belonging 

 to this group are coarse-grained, pegmatitic rocks, consisting of felspars 

 (light-reddish orthoclase and white plagioclase), quartz and black biotite. 

 They form intrusions in the amphibolites and gneiss-rocks. The middle 

 part of the intrusions shows as prominent minerals felspars and quartz with 

 less abundant biotite. The composition is rather granitic ; the felspars are 

 in excess over quartz. The size of the grains is more than 2 cm. To- 

 wards the border of the pegmatite the orthoclase disappears, the contents 

 of mica increasing with decreasing amount of plagioclase and quartz. 

 According to the mineral composition the border-rock of the pegmatite 

 (the "sahl-band") is like a quartz-mica-diorite. The sahl-band shows indi- 

 cations of "Augenstructure" due to the quadrangular or rounded plagio- 

 clases in the black mica. Along the exact border of the pegmatite is 

 shown a dark band of pure biotite. 



Vid. -Selsk. Skrifter. I. M.-N. Kl. 1915. No. 4. 2 



