| AN dd -k ba Nana AR og FSD SONEN 
16 | Pentti Eskola. ; (LXI 
Toscanose (1, 4, 2, 3). 
The Osann figures: 
S A & F (ARG JES k 
T 
71.80” 7.76, 2430 17:82. 18:51 3.080 SS 
The constituent minerals are, named in the order [01 ENE 
their abundance: Plagioclase, microcline with some albite, 
quartz, biotite (with secondary chlorite), hornblende (dark 
green), titanite (euhedral crystals and leucoxene), magnetite, 
apatite, orthite and epidote. 
The actual feldspars are plagioclase (oligoclase) 
and microline-perthite. The plagioclase forms, 
together with quartz and some microcline, the medium- 
granular (millimeter-grained) ground-mass of the porphyritiec 
rock. It shows, in sections | PM, an extinction angle of 
+ 4”. Its refractive indices are all higher than that of the 
Canada balsam. A comparison with the quartz gave the 
result: «' <w; y' > w. Thus the composition of the plagio- 
clase 1s approximatively Ab,s;. Towards the microcline the 
plagioclase grains are bounded by albitic borders. 
Orthite, with e pi d ot e, is remarkable because being 
a very constant accessory in all the igneous rocks of Sviatoy 
Noss. The mode of occurrence is always the same: minute 
euhedral and strongly pleochroic brown crystals of orthite 
are surrounded by a much larger zone of faintly greenish 
epidote. They will be described in more detail under the 
sviatonossite in which they are still more prominent consti- 
tuents. The other minerals do not call for any comments. 
In the qualitative system of igneous rocks, as modified - 
by Iddings, this rock classes itself with the granodiori- 
t es 1), having alkali-feldspar and lime-soda-feldspar in nearly 
equal amounts, within the ratios 5 : 3 and 3: 5 and the latter 
exceeding. As, in the present paper, I will generally follow 
Idding's classification, this term will be used here. It may, 
however, be remarked that in this particular case it would 
perhaps be more rational to call this rock quartz-monzonite, 
which term, according to Iddings, is applied to rocks closely 
2) J. Iddings, »Igneous Rocks>, II, p. 69. New York, 1913. 
