Ger 
ÖRE 
AA N:o 1) Igneous Rocks of Sviatoy Noss in Transbaikalia. 13 
Diorite. 
Among the rocks of Sviatoy Noss older than the igneous 
complex of the granites there are also such types which 
may be safely termed as primarily igneous or eruptivogeneous, 
and such of these that have some primary structural features 
preserved may be mentioned here. Those having a dioritic 
composition are all plutonogeneous. The amphibolites never 
have preserved any structural features pointing to a volcanic 
Origin. 
Diorite-gneiss. 
One of the most typical plutonogeneous rocks is a diorite- 
gneiss observed at several points in the southern part of 
— Sviatoy Noss, e. g. at points 7 and 35. At the former locality, 
near the South Cape, the diorite-gneiss occupies an elongated 
area, being, in the shore-cliff, exposed about 50 meters 
obliquely to the strike. The occurrence at point 35, a few 
kilometers further North, is somewhat less extensive. 
This rock is megascopically distinctly foliated and pre- 
 sents a double granularity: The biotite and hornblende form 
flattened groups arranged along the strike and giving the 
rock its characteristic gneissoid appearance, and between 
them there are light spots of granular plagioclase. 
The following constituents were detected under the 
— microscope, named in the order of their relative abundance: 
 Plagioclase, TIER quartz, hornblende, titanite, iron ore, 
— apatite. 
The plagioclase between crossed nicols appears 
spotted in consequence of unequal extinction, but no regular 
zonality can be observed. Its composition varies from 
about ÅAbss to Ab,,. 
| The hornblende is very dark-coloured and has 
: a strong pleochroism: « = yellowish green, p = dark olive 
green, nearly opaque in the section, y dark bluish green. 
FAbsorption: o<pP>y-c:y = about 22”, pg = b and the 
j negative acute axial angle 2 E is about 60” or 2 V =35", 
fupposing p to be 1,68. These characters point to a horn- 
