RESET STEN IM 
A N:o 1) Igneous Rocks of Sviatoy Noss in Transbaikalia. 45 
7) Titanite-aplite, with large (up to 1 cm in diameter) 
crystals of titanite and very small amounts of altered pyro- 
xene or amphibole. This is a common type among the dike- 
rocks of the sviatonossite-series, and it is a fact of much 
interest that these dike-rocks also often contain graphite. 
The syenitic rocks found in the shore-drift near Markova 
are in part andradite-syenites of types 1) and 2), in part 
pyroxene-syenites. All varieties found here are porphyritic. 
The syenites and pyroxene-granites at points 74 A and 75 A 
are aplitic light-coloured varieties. 
Two principal kinds of sviatonossite. 
On merely megascopic inspection the sviatonossites seemed 
-to present quite an irregular variability. On microscopic 
examination of a large number of .specimens it appeared, 
Kowever, that this great multitude of various types can 
be dealt with under two principal headings which, chemically 
as well as structurally, show some distinctive features. 
I. The specimens of rocks belonging to the first group 
contain perthitic feldspar. This mineral builds up large 
Karlsbad twins which, as a rule, appear as phenocrysts. The 
feldspar of the granular ground-mass consists of potash 
feldspar and plagioclase in separate grains. The plagioclase 
contains more than 80 percent Ab. To this group belong all 
the varieties rich in pyroxene. 
II. The rocks of the second group do not contain perth- 
itic feldspar. Therefore their structure is non-porphyritic, 
unless the andradite happens to have a phenocrystal develop- 
ment. In the absence of the large perthite individuals the 
granular plagioclase-potash-feldspar mass is preponderating 
and, the mafic minerals often being scarce, the rocks ap- 
proach aplites in their general habit. The plagioclase was 
almost invariably found to be more anorthitic than in the 
representatives of the former group, containing from 70 to 
80 percent Ab. The pyroxene is present in rather small 
amounts, if at all. Epidote and orthite are abundant. 
