14 Pentti Eskola. (LXTIE 
blende rich in ferric as well as ferrous oxide. The bio- 
tite also is very dark (brown) in colour. 
Titanite is remarkably abundant, as well- formed . 
crystals. 
"Anatectic amphibolite. 
As already mentioned, there are, among the ampbibolites 
on the peninsula of Sviatoy Noss, many examples of rocks 
whose origin can not be stated with any certainty. Whatever 
they may have been originally, most of the amphibolites 
are, in their structure, very like igneous rocks, also in such 
cases, where their geological occurrence points to a sedi- 
mentogeneous origin. They may then have undergone some 
kind of anatectic recrystallization. Under the microscope 
such rocks are usually seen to be composed chiefly of plagio- 
clase and hornblende and quartz, the first-named ranging 
from oligoclase-andesine to labradorite. Thus they would. 
chiefly belong to the quartzdiorites, if treated as igneous 
rocks. A structural feature of interest is the common xeno- 
morphity of the hornblende towards the plagioclase, char- 
acteristic of many hornblende-gabbros and hornblende- 
diorites, while the average amphibolites having typical 
granoblastic structure have idiomorphic, or idioblastic, 
hornblende, this mineral having a more advanced position 
in the crystalloblastic series than the plagioclase. Another 
feature common in these amphibolites is the zonal structure 
in plagioclase with cores more anorthitic than the margins. 
Granites and Granodiorites. 
The inner part of the Tshivirkouy Bay and the eastern 
Sviatoy Noss are apparently underlain by coarse-grained 
granitic and granodioritic rocks. This vast massif continues, 
in an easterly direction, over the Tshivirkouy Mountains 
into the Bargousin valley. 
In the migmatitic area of Sviatoy Noss were rocks of 
characteristically similar structure and composition occasion- 
ally met with as small lenticular intrusions. 
