6 Pentti Eskola. . (exmn 
trusives have the composition of diorites and gabbros. They. i 
are foliated and metamorphosed to a considerable degree 
and seem to form sill-like bodies folded together with the =: 
other rocks of the metamorphic series. They are cut across 
by the dikes of aplite and pegmatite and also by the granitic | 
Veins. 
Among the crystalline schists of the migmatitic comin St 
the gneisses are represented in a great number of va- = 
rieties. Among these the various augengneisses call 
for special attention. They are biotite- or biotite-hornblende- = 
gneisses containing large »eyes» of microcline surrounded by 
scales of biotite. The eyes may pass over into small lenses 
of feldspar and quartz and further into granitic veinlets. 
In such cases the peculiar structure of the rock may either 
be referred to an ultra-metamorphism or to a beginning =: 
granitization. At other points the augengneiss has a ground- 
mass showing massive structure and medium grain. The - 
rock is then very like the coarse porphyritic granite: and - 
may have been derived from them. Some examples bear 
resemblance to quartz-porphyries, having a fine-crystalline 
ground mass. — Thus it seems to me probable that the 
augengneisses on Sviatoy Noss may be of various origin. 
Many examples of gneisses have a coarsely crystalline 
structure, so that their origin can not by any means be 
stated. There are grey mica-gneisses of medium grain, and 
plagioclase-amphibole-gneisses grading into amphibolites by 
decrease to the quartz. These varieties, as well as the augen- k 
gneisses, have commonly been injected with granitic veins 
to form adergneisses or arterites (fig. 3) representing the - 
most common kind of migmatite on Sviatoy Noss. The - 
primary nature of such rocks, of course, can not possibly 5 
be interpreted. 
The amphibole-plagioclasegneisses and - 
the amphibolites (metamorphic plagioclase-hornblende- 
rocks) are very common in all parts of Sviatoy Noss, occurring 
also as fragments in the large masses of granite. The amphi- 
bole-bearing schists have all been very thoroughly meta- 
morphosed, and no traces of their primary structure have 
