269 
but contact metamorphosed dyke has been found in the quartzitic 
sandstone on Mt. Iganek, it is perhaps a direct continuation of 
the former. 
Augite-syenite-porphyry. — A common sort of dyke in 
this region has a dark reddish-brown ground mass of a fine- 
grained or almost dense structure and phenocrysts of white 
felspar. These are tabular and, as a rule, they do not exceed 
| centimeter. They consist of alkali-felspar, most often soda- 
orthoclase. The ground mass is of a trachytoid structure, 
and is mainly made up of small laths of orthoclase and 
albite; in some cases these laths are perthitic, in others the 
orthoclase forms the centre of the crystals, whilst the mar- 
ginal zone is albite. The felspar is thoroughly saturated with 
red ferric oxides. The other constituents of the ground mass 
are: gray and green augite, green biotite, a little apatite, and 
tiny grains of iron ore. Chlorite, calcite, and brown iron oxides 
commonly occur as secondary products. 
Hedrumite. — The recently described type of dyke rocks 
is by transitions connected with a type which may be charac- 
terized as hedrumite!. The dykes of this type are almost as 
common as are the augite-syenite-porphyries, and some of 
them are very wide. Thus one dyke north of the Igaliko 
houses is about 40 meters wide. The colour is dark brownish- 
red or gray, the structure is fine-grained and trachytoid. The 
parallel arrangement of the small felspar tables imparts to the 
rock a slight silky lustre when it is split parallel to the direc- 
tion of the flow structure. Phenocrysts are absent. The main 
constituent is a perthitic alkali-felspar. Aggregates of muscovite 
replace the nepheline and are present in varying, but on the 
whole, small quantities. The ferromagnesian minerals are a light 
gray augite, egirine-augite, ægirine, brownish-green biotite, and 
7 W. C. BRÖGGER, Die Eruptivgesteine des Kristianiagebietes III (1898), 
р. 183. 
