14 



J. SCHETELIG. 



M.-N. Kl. 



orthoclase. The sections are bordered with orientated margins of albite 

 (Anrj). Myrmekite partly together with secondary muscovite is not un- 

 commonly present along the borders and between the sections of ortho- 

 clase. The potash-felspar is in most cases in distinct excess over the 

 plagioclase. In one slice the content of plagioclase is ver}' low, only a 

 few small grains being seen between the sections of microcline, bordered 

 as usually with albite. This rock corresponds with the pure potash-granite 

 described from Mt. Betty. 



Fig. 5. Granite (analysed) Scotts Nunataks. Micro-Photo. Niçois -t- . Enlarg. 17. 



In Other slices the content of plagioclase is greater than in the ordinary 

 type, thus showing a passage into a type similar to the plagioclase-granite 

 from Mt. Betty. 



The plagioclase often shows zonal structure with a central part of 

 oligoclase (Ano.-j — > Anao) or oligoclase-andesine (Ango -^ Ang^) and a border 

 of albite (An^). The percentage of the anorthite-silicate in the plagioclase 

 is calculated from Beckes tables, according to determination of the ex- 

 tinction-angle «' in sections -j- the axis a. 



The small plagioclases are idiomorphic against orthoclase and quartz; 

 but the large sections of plagioclase as well as orthoclase contain on the 

 contrary small idiomorphic grains of quartz, crystallised earlier than or 

 simultaneous!}' with the felspar. 



The major portion of the quartz has crystallised later than the ortho- 

 clase as mesostasis. In part the quartz shows mechanical deformation due 

 to stress, the grains being cracked and crushed with undulatory extinction. 



