278 
gates of a colourless mica. The ægirine is also abundant; it is 
allotriomorphic. The very few phenoerysts consist of a dull white 
felspar of the same kind as the felspar phenocrysts of the cen- 
tral part of the dyke. 
Chemical composition. — According to the analysis by Dr. 
Wintuer, the central part of the dyke has the composition given 
in the above table (No. 28, see p. 275). The marginal zones have 
not been analyzed. 
Hedrumite of Akuliarusek. 
Among the dykes of Akuliarusek on the Igaliko Fjord several 
instances of a type which may be characterized as hedrumite 
have been found (vide p. 269). These dykes probably repre- 
sent transitional forms between the foyaitic and the syenitic 
dykes. 
The rock to be described in the following lines constitutes 
a three meters wide dyke running from N. 40° E. to S. 40° W.; 
it was found at a liltle distance south of the last mentioned ne- 
pheline-porphyry. The rock is fine-grained and devoid of pheno- 
crysts. The structure is trachytoid. The main constituent of the 
rock is a felspar which is developed in tabular crystals about 1 
millimeter long with a fluxional arrangement. Under the mi- 
croscope the felspar tables are seen to be made up of ortho- 
clase and plagioclase in perthitic intergrowth. The composition 
surfaces of the two felspars are about parallel to (010). The 
orthoclase is a little clouded and locally it is microcline-like, 
showing an indistinct and irregular twin structure. The plagio- 
clase has the optic characteristics of albite, or of an oligoclase- 
albite poor in lime. Between the felspars allotriomorphic ag- 
gregates of muscovite occur in rather small quantities. These 
aggregates are probably secondary replacing nepheline, but 
fresh nepheline has not been found. The femic minerals of this 
rock are the following: brownish-green hornblende (с : с = ca. 16°), 
