250 
Dykes cutting the augite-syenite. 
Only some few dykes have been observed in the augite- 
syenite, but as the greater part of the syenite area is covered 
with rubbish, several dykes may have been overlooked. An 
aplitic dyke was found in the little valley north of the Iganek 
Mountain at a place lying about 250 meters above sea level. 
This dyke is only 1'3 meter wide; it is quartz-bearing and 
fine-grained, the colour being gray. A narrow marginal zone 
on each side consists of a black glassy material with pheno- 
crysts of white felspar showing broadly rectangular sections of 
a length of 1 or 2 millimeters enly. 
A more peculiar dyke was found near the river south of 
the Narsarsuk Plateau a little above the water-fall made by this 
river where it falls on to the low granite area north of the 
Igaliko Fjord. The dyke is a tinguaite. It is five meters wide, 
and runs from Е.М. Е. to У. $. W., the same direction as most 
of the dykes in the sandstone territory. The rock is a grayish- 
green porphyry with a fine-grained ground mass; in the border 
facies the ground mass is dense and the colour a clearer green. 
This dyke is specially interesting as it contains scarce quartz- 
like grains 3—5 millimeters in size which are probably extraneous 
inclusions in the rock, and which on closer investigation proved 
to be cordierite. They have the appearance of milky quartz and 
are rich in minute inclusions which are needle-shaped and 
arranged parallel to the least axis of optic elasticity, whilst other 
inclusions consisting of small rounded pyroxene-like grains are 
arranged in rows at right angles to the former. The mineral is 
optic biaxial, and has a mean index of refraction slightly lower 
than that of the Canada balsam. The microscopic test which 
indicated the presence of large quantities of magnesium moreover 
proved the identity of the mineral with cordierite. The ordinary 
phenocrysts of the rock consist of a clear orthoclase in rather 
scarce large tables, about 10 millimeters by 3—5 millimeters. The 
