113 
quantities. Probably it is an alteration-product of the dark- 
coloured minerals of the rock. 
Structure. — The structure of the arfvedsonite-granite is 
hypidiomorphic-granular without any tendency to parallel ar- 
rangement of the elongated mineral-components. A characteri- 
stic feature is the almost complete absence of minor accessories 
(apatite, zircon, and iron ores) among the first crystallised 
minerals of the rock. If the ægirine-microlites are left out of 
consideration the felspar is the most idiomorphic and the arfved- 
sonite the least idiomorphic constituent. A marked idiomorphism 
of the felspar, however, is only observed in a few varieties of 
the rock; in such cases the felspar sections are broad and 
rectangular while quartz and arfvedsonite fill the interspaces 
between them. More commonly the structure points to a si- 
multaneous crystallisation of felspar and quartz the grains of 
the latter mineral being more or less rounded. Micropegmatitic 
intergrowths of felspar and quartz are also observed, though 
not very often. The arfvedsonite is always allotriomorphic when 
bounded by felspar, and as a rule the same holds true when it 
borders upon quartz. The ainigmatite is older than the arfved- 
sonite but its age in relation to the other minerals is un- 
known. 
Chemical composition. — A chemical analysis of this rock 
has been made by Dr. Winter with the results given in 1 of 
the following table. The specimens selected for analysis were 
of a fresh-looking, light grayish-brown variety collected at an 
altitude of 450 meters, above North Siorarsuit. From this ana- 
lysis we may reckon that the rock has the following approxi- 
mate mineral composition: — 
Per cent 
Kelspan® 2... ME 64 
Quartz. 916.420 24 
Ainigmatite ...... 3 
Arfvedsonite...... 9 
100 
XXXVIIL 8 
