270 
dark brownish-green hornblende. A more complete description 
with chemical analysis of a dyke of this kind is given below 
(p. 278). 
Nepheline-porphyry. — Dykes of this kind are found in 
different parts of the Igaliko region, but are not common. The 
petrographie description is given below (p. 274). 
Sölvsbergite(2). — In the vicinity of the landing place at 
Igaliko two tinguaitic dykes are found. One is 5 meters wide, 
and the other 8 meters. Both strike from Е. N. Е. to W. S. W. 
The ground mass is grayish-green, dense or very fine-grained. 
Under the microscope it shows a typical tinguaitic structure. It 
consists of fine ægirine needles distributed evenly, but without 
parallel arrangement over an aggregate of salic mineral grains 
which are mainly microcline. 
Age of dykes. — As far as observation goes, the dykes are 
later than the sandstone, and, as a rule, they are also younger 
than the sills between the sandstone beds, for the sills in a 
great many instances are seen to be cut by the dykes. Only 
once, as mentioned by Dr. Steenstrup”, is a diabase sill seen 
to be in direct connection with a dyke of the same rock. 
It is difficult at present to give a satisfactory answer to the 
questions as to the age of the different kind of dykes in rela- 
tion to one another, and to the abyssal rocks of the Igaliko 
batholite. These questions are evidently of great importance 
from a theoretical point of view, but they will require much 
additional field work for their entire solution. 
Still it is possible from the observations in hand to draw 
certain conclusions as regards the age of the different dykes. 
On the one hand it may be regarded as established that, whilst 
dykes are rather rare in the augite-syenite and the nepheline- 
syenite, they occur much more frequently in the closest abut- 
ting areas of basement granite and sandstone, as for instance 
1 Meddelelser om Gronland XXXIV, 1909, р. 126. 
