A N:o 1) Igneous Rocks of Sviatoy Noss in Transbaikalia. 65 
in smaller amounts, in the form of minute, scattered irregular 
grains. The colour is:a rather intense green and the optical 
properties indicate no less amount of aegirite to be present 
than in the example of this mineral used for the mineral 
analysis: 
The titanite and apatite do not call for any spe- 
cial comment beyond the description already given. 
The epidote, with orthite, has chiefly the same 
mode of occurrence already described, but they are here 
more frequent, in the form of inclusions as well as in separate 
grains.. In the calculated mode, however, they were left 
out of consideration, as in this specimen they are not very 
abundant. in many other specimens the epidote and orthite 
must be regarded as characteristic ordinary constituents. 
There are two different kinds of epidote in this rock: one 
occurring as dusty alteration-products or as minute anhedral 
inclusions in the andradite and pyroxene and another forming 
independent grains apart from the mafic minerals, the epi- 
dote having separated around cores of orthite. The former 
kind of epidote is secondary, the latter is of a primary, i. e. 
magmatic origin. 
The orthite, forming the core of the epidote grains, is 
— idiomorphic and euhedral. The crystals are tabular after 
oo othe orthopinacoid (100) and their best developed simple 
forms are (100), (010), (001) and (101). Twinning on (100) 
Was sometimes observed. The size of the grains is about 
one mm in longer diameter; sometimes more. The mineral 
is idiomorphic towards the feldspars, the pyroxene and the 
andradite, but xenomorphic towards the apatite and the 
titanite. The orthite is optically negative with a large axial : 
angle (larger than that of the epidote). The axial plane 
lies at right angles to the trace of the best cleavage, or 
in the plane of symmetry; the angle c:c is 32” or 33” in the 
acute angle fP. The pleochroism is exceedingly strong: co 
= pale greyish brown, £ = dark chestnut brown, y dark 
sepia brown. The formula of absorption is « <fP>y. The 
birefringence (7—0) is approximately 0.035, or but slightly 
lower than in the epidote, in which it was estimated at 0.038. 
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MET POTY TEST IE TYVIIKPESRIKTYS v 
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