A N:o 1) Igneous Rocks of Sviatoy Noss in Transbaikalia. 43 
exposed at point 74 A on the beach, and at point 75 A 
similar whitish granite is found in the form of large blocks 
that can not have been transported any long ways. 
The sviatonossite displays great variation inits structure as 
well as in its composition. Porphyritic types have phenocrysts 
of perthitic feldspar. Some varieties contain only andradite 
as a mafic mineral, in others there is much pyroxene. Many 
specimens are destitute of garnet, and the rocks are normal 
pyroxene-syenites. In many places the sviatonossite grades 
into syenite-aplite by disappearance of the garnet and pyro- 
xene. In most specimens no quartz could be detected under 
the microscope, whilst some contain small quantites of”this 
mineral and rarely (north of Markova) the rock grades into 
true granites rich in quartz. Further considerable diversity 
in the chemical nature of these rocks is due to the variation 
of the composition of the plagioclase and the quantitative 
ratio of the plagioclase and the potash feldspar. In most 
of the specimens collected from the actual outcrops the 
plagioclase is comparatively rich in anorthite, the rocks 
being at the same time even-grained and, as a rule, poor in 
pyroxene. Gradual transitions into aplitic and quartz-. 
bearing types are here common. At point 59 B the homo- 
geneous rock is cut by some primary dikes, but slightly 
different from their country-rock, and other dikes of aplite 
and pegmatite containing much quartz. Going towards the 
southeast the grains of andradite in the main rock grow 
smaller, and the whole appearance of the rock becomes 
aplitic, sodic plagioclase being the chief constituent. At 
first andradite is still present (point 60 B), but then dis- 
appears and is replaced by quartz (point 61 B), and, at point 
62 B, the whole eruptive mass is bounded by a schistose 
rock. | 
At point 51 A the sviatonossite shows more irregularity 
in its characters. The place is a ravine on the slope. On 
the northeastern wall of the ravine syenitic rocks without 
or with very little garnet were observed. On the' south- 
western wall there was found sviatonossite in several varieties 
and mixed with syenites. The sviatonossite is either coarse- 
