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N:o 1) Igneous Rocks of Sviatoy Noss in Transbaikalia. 39 
to the fact that the limestones in this region are graphite- 
bearing. 
The diopside-pegmatite occurs as rather narrow dikes, 
as a rule not exceeding one meter in breadth. Where broader 
dikes are seen in their vicinity, these are common pegmatite 
dikes containing micas or hornblende, but no diopside or 
titanite. | : 
The diopside-pegmatite is of a considerable interest 
from the petrological point of view, as it exhibits an example 
of assimilation of the country-rock by pegmatite, a magma 
which, after all probability, has never been heated to any 
high temperature when intruded. 
Hornblende-pegmatite. 
On the shore between North Cape and the isle of Kyltyghey 
were found dikes of pegmatite of a type which in numerous 
occurrences  preserves approximately the same structural 
and chemical characters. It is only rarely truly pegmatitic 
with coarse-grained quartz-feldspar-mass, but more often 
composed of a medium-grained feldspar in which are em- 
bedded large groups of biotite and hornblende. This biotite- 
hornblende-pegmatite occurs only in the hornblende-gneiss 
and probablyits composition is in part owing to an assimila- 
tion of the country-rock. The mica groups as well as the 
hornblende crystals are in part arranged in the direction of 
the dikes which is usually the same as that of the foliation 
of the country-rock. Many of them attain a considerable 
breadth, up to several meters. 
This pegmatite is remarkable because containing more 
orthite than any other kinds of pegmatite on Sviatoy 
Noss. Most dikes contain at least some minute crystals and 
at places rather numerous and comparatively large, up to 
2 cm in maximum diameter. In greatest frequency we met 
with them at the shore about 4 or 5 kilometers from the 
North Cape towards the Molodost Bay. The pegmatite is 
here found as rather narrow dikes, less than one meter in 
, thickness, and their rock is aplitic in ground-mass but speckled 
