A N:o 1) Igneous Rocks of Sviatoy Noss in Transbaikalia. 41 
and with hornblende as a rather abundant mafic mineral. 
One is inclined to suspect genetical connection with its 
country-rock. The latter is amphibolite, in part amphibole- 
gneiss. Similarity in the composition is therefore quite 
apparent. As the country-rock is a metamorphic rock with 
pronounced foliation which no doubt is of metamorphic 
nature, we cannot suppose any segregation from common 
magma. It seems far more plausible to think of a digestion 
of the amphibolites by the pegmatitic exhalations, resulting 
in a pegmatitic rock resembling in its composition the sur- 
-rounding amphibolitic rock. 
In the same tract where the aplitic pegmatite rich in 
orthite occurs there are other dikes of common pegmatite, 
usually containing prevalent potash feldspar and large 
amounts of quartz, besides either biotite or muscovite or 
both kinds of mica at the same time. At numerous points 
on the shores of the Tshivirkouy Bay were found, in the 
 shore-beach, blocks of pegmatite containing large crystals 
of black tourmaline. 
The orthite-bearing biotite- -hornblende-pegmatite is older 
than all the other dikes of pegmatite in this tract and is 
cut sharply across by them. 
The Sviatonossites (andradite-syenites) and Related Rocks. 
The occurrences. 
A peculiar rock-type found on the peninsula of Sviatoy 
Noss contains andradite and aegirite-augite. The felsic con- 
stituents are represented only by feldspars which are, in 
most cases, highly alkaline, i. e. potash feldspar in perthitic 
intergrowth with soda feldspar, and plagioclase, very rich 
in the albite-compound. Thus the rock has the felsic minerals 
of a true syenite, and from its peculiar mafic constituent 
it could be called andradite-syenite. In its bulk composi- 
tion, however, this rock is very far from any syenite. 
An outcrop of the sviatonossite was first found 
on the western slope of the Sviatoy Noss mountains, at point 
