271 
on the Narsarsuk Plateau and Mt. Iganek. Furthermore, almost 
all the specimens of dyke rocks collected from these places are 
greatly contact metamorphosed. Thus we arrive at the conclu- 
sion that the majority of dykes are older than the ba- 
tholite. But the diabase dykes and the numerous reddish- 
brown porphyry dykes in the environs of Igaliko must probably 
be reckoned among this older group. 
As pointed out in the foregoing, on the other hand, dykes 
have been found which intersect the augite-syenite and the 
nepheline-syenite. A small number of the dykes are 
thus of later origin than the batholite. It is of in- 
terest that most of these younger dykes have the same direc- 
tion as the older ones. The tinguaitic dykes mentioned on p. 
237 and p. 250, and most probably also the sölvsbergites men- 
tioned above, belong to these younger dykes. It has been 
mentioned {p. 237) that the syenite-porphyries are also repre- 
sented in the younger series. That diabase dykes of this series 
have not been found in the Igaliko territory is probably only 
due to the cursory nature of the field work undertaken. The 
existence of the younger series of dykes is of importance to 
the apprehension of the geological history of the district; it 
shows that we must look at it as not impossible, perhaps even 
probable, that the volcanic activity on the surface of the 
earth has continued as late as down to the time when a large 
part of the batholites became solidified, even if the main part 
of the volcanic phase be older than the batholite. 
PETROGRAPHY OF NEPHELINE-PORPHYRIES 
AND RELATED DYKE-ROCKS. 
As already mentioned foyaitic dyke-rocks are of rather 
common occurrence in the Igaliko district. They belong to a 
number of different types, of which the most important will be 
described in the following pages. 
