834 TR Pont BSköla (LXIIT 
characters of the pyroxene and feldspar. In the former rock the 5 z 
pyroxene has colours which from a description only cannot 
be said to differ from those of our pyroxene, but the extinc- 
tion angle c: a« is 31”, the smallest value that I have observed 
here being 35”. This fact indicates a slightly higher percentage 
of aegirite in the pyroxene of the malignite and the same 
conclusion may be drawn from the analysis which gives 
normative acmite, though the pyroxene no doubt contains 
some alumina, which fact causes the norm to show less acmite = 
than is actually present in the aegirite-augite. Another 
difference between the two rocks may be found in the feldspar. 
The plagioclase in microperthitic intergrowth with the ortho- 
clase in the malignite is almost pure albite, showing on P och 
(001) extinction angles of 16” to 18”. In the sviatonossites = 
the perthitic plagioclase contains appreciable amounts of 
anorthite, usually about 15 2. Both these characters, shared 
also by the two other kinds mentioned above, prove the 
malignites to be more decidedly alkaline rocks. Such is also 
the case with the malignites from the Kruger alkaline body, 
"according to Daly associated with nephelite-syenites. The 
sviatonossites, on the other hand, are intermediate between i 
the two principal branches of igneous rocks. It was chiefly 
for this reason that I have not classed the andradite-bearing 
rocks from Sviatoy Noss with the malignites, in spite of 
the very close analogies. The fact that some of the maligni- 
tes contain nephelite, a mineral which has not been observed 
in any of the Sviatoy Noss rocks, seems here to be of less 
importance, the formation of nephelite being simply a 
consequence of a deficiency of silica, which in the course of 
the differentiation process might have very well been arrived 
at in a rock like the sviatonossite. 
The intrusive mass of the malignites on Poohbah Lake 
»has a roughly elliptical shape in ground plan, with a longer 
diameter of not less than six miles, and a shorter diameter 
of about three miles». The nephelite-bearing variety, being 
the most femic one, occupies several isolated areas in the 
inner part of the mass, while the whole southern and larger 
part of the rnass is made up of the garnet-malignite and the 
2 
Fd 
