1915. No. 4. REPORT ON ROCK-SPECIMENS. 



Biotite is less abundant. The fresh mineral shows strong absorption: 

 ß and ;' dark reddish brown, a straw-yellow. Pleochroic halos surrounding 

 included minute zircons are always present. The mineral is partly altered 

 into chlorite. 



Muscovite is ver}^ sparingl}' present. 



Apatite is shown in all slices, but generally in very small amounts. 

 In the slice of the pure potash-granite however man}' irregular grains are 

 seen up to 2 mm. in size. 



Zircon is generally present as inclusions in biotite; a few small grains 

 sometimes elsewhere also are seen. 



Magnetite occurs very sparingly. 



The above mentioned fine-grained granite of dark gray colour differs 

 from the ordinarv type only in its greater content of plagioclase, biotite 

 and magnetite. However the minerals in the two types of granite are 

 identical, and undoubtedly the two granites are closely related to each-other. 



The chemical composition of the medium-grained, light granite, the 

 common type from Scott's Nunataks, is shown from the following analysis 

 (No. 3), at my request kindly undertaken by Dr. Naima Sahlbom. For the 

 sake of comparison the analysis (No. i) of the white aplitic granite from 

 Mt. Betty is subjoined. 



No. 3. Granite. Scott's Xiinataks. No. i. Aplitic granite. 

 Analvst: Naima Sahlbom. Mt. Betty. 



