193 
e:c is 42°. It only seldom shows inclusions of the black mi- 
crolites so common in the augile of the augite-syenite. Some- 
times it is accompanied by ægirine-augite. Less frequently 
ægirine occurs in the nordmarkite and when such is the case 
the augite is wanting. 
Hornblende in large quite allotriomorphic anhedra is com- 
monly the predominant dark mineral. In sections parallel to 
the plane of symmetry (010) the angle of extinction e:c has 
been found to be from 15 to 25°, somewhat different in the 
different specimens. The absorption tints are rather varying 
with a light brown or yellowish green, while 6 and c show 
dark green, brown or sometimes bluish brown colours. A thin 
blue marginal zone, in which the angie of extinction e:c is a 
little greater than in the interior, is often seen. In varieties of 
the rock which are richer in quartz the usual hornblende may 
be replaced by arfvedsonite. Ainigmatite has only been observed 
as an occasional, subordinate component. 
The felspar is chiefly an alkali-felspar of complicated per- 
thitic structure and shows a somewhat varying form and habit 
in the different specimens. The size of grain averages about 
half a centimeter and the shape is rather irregular, often tend- 
ing to a form that gives broadly tabular sections, or in other 
specimens with a tendency to a more elongated, rhomboidal 
form. In the latter case the felspar-crystals may attain a length 
of 3 centimeters. 
In the varieties of the rock where quartz is almost entirely 
absent, the felspar is a soda-orthoclase in microperthitic inter- 
growth with oligoclase. In sections parallel to 5 (010) the main 
portion is optically homogeneous with an extinction angle of 
+ 9°. Locally, however, a very fine cryptoperthitic lamellation, 
under an angle of 72 or 73° with the cleavage-traces, is seen 
under high magnification. This is due to an alternation of 
lamella of only slightly different index of refraction and the 
‘lamellation is best seen in non-polarized light. In the more 
XXXVIII. 13 
