RA PRESS BSTN 
FÅ de 
A N:o 1) Igneous Rocks of Sviatoy Noss in Transbaikalia. 73 
in the ratio 1:21 for pyroxene, and the remaining SiO,, was 
reckoned as quartz. The following figures were arrived at: 
(arbe NS FAS RÅ 18.48 
MiGCTOCINO dvinat tort dgr 35.58 
Plagioclase NA NNE FINT 
(Abs;-Ans;) [Anorthite-.; 1.39] 
NaFeSizOg ol 
Pyroxene |a5i, ES fc | 5.83 
-CaSiO3 0.81 Ne 
1 230 BEMÖTTA KANAL RAR en ASSR 0.78 
APA boorosn sena SENS NOT 
According to this calculation the pla gio clas e should 
have the mean composition of Aby,Ang. This result agrees 
fairly well with the microscopical examination. The refring- 
ence as compared with that of the quartz is w > y,. The 
extinction angle in several sections | PM was found to be 
13” indicating about 97 percent Ab. This albitic plagioclase 
is homogeneous and has no still more sodic borders. It is 
very finely twinned according to the albite and pericline 
laws. The twinning lamellae are frequently bent or broken. 
The potash feldspar is cross-hatched microcline 
containing but trifling amounts of fine bands of albite in 
perthitic intergrowth. ; 
The quartz has a strongly undulatory extinction. 
The direction of the »waves» is always approximately parallel 
to w 3). ; 
The pyroxene, according to the calculated mode, 
should have the composition: 14 mol. NaFeSi;Og, 9 mol. 
FeSiOz, 6 mol. MgSiO, and 7 mol. CaSiOs, or in percent of 
weight (1): 
1) Cf. P. Eskola, »On the Petrology of the Orijärvi Regiom»>. Bull. Comm. 
Géol. Finl. N:o 40, p. 33, (1914). 
