234 
In most specimens of the foyaite the felspar is very fresh 
and clear or only a little clouded, but in other specimens which 
apparently are no less fresh many of the felspar crystals are 
seen to contain small irregular grains or patches of clear 
calcite. 
Nepheline occurs very abundantly. The crystals are fresh, 
or contain only a small quantity of secondary muscovite. At 
their border they have frequently been partially converted into 
natrolite. The nepheline is sometimes a little more and some- 
times a little less idiomorphic than the felspar. Cancrinite is 
entirely absent in many specimens, but in others it is relatively 
abundant. It occurs in large lapped anhedra filling the inter- 
stices between the crystals of felspar and nepheline. Sodalite 
is another occasional constituent of the rock, but the quantity 
of it is never large. Sometimes it is interstitial, sometimes it 
occurs aS a magmatic alteration product of the nepheline. 
As to structural details observed under the microscope it 
may be noted that the dark-coloured minerals, though as a 
rule disseminated through the rock or occurring in irregular 
intergrowths, in some few specimens show a tendency towards 
concentric arrangement. This peculiarity is especially well de- 
veloped in a medium-grained nepheline-syenite collected at the 
coast due N. of Igdlerfigsalik. In this rock the dark-coloured 
minerals are crowded together in patches which consist of an 
aggregate of ægirine-augite surrounded by hornblende which, in 
its turn, is surrounded by biotite. 
Chemical composition. — The chemical analysis of the 
rock is given in the first column of the following table. The 
specimens selected for analysis were taken N. N. W. of Igdler- 
figsalik at the south coast of the Korok Fjord. Mineralogically, 
they are of the ordinary type: egirine-augite predominates 
among the dark minerals, and sodalite and cancrinite are pre- 
sent only in very small quantities. The structure shows some 
tendency towards the porphyritic. 
