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porphyry, which is very common as dyke-rock in the whole 
region, also occurs as sills; thus on the west side of Mount 
Steenstrup, at a height of 540 meters and also nearer the top. 
At the former place the rock contains a little quartz. 
Dykes cutting the volcanic series. — The volcanic series 
of Ilimausak is cut by a large number of dykes. Most of them 
are strictly vertical and run in a direction corresponding to the 
main direction of the fjords (about N. 60° E.); as a rule they 
do not penetrate into the abyssal complex. 
The commonest dykes are composed of a bluish-gray or 
reddish-gray syenite-porphyry; their ground-mass is fine-grained 
and usually (not always) devoid of quartz; the phenocrysts are 
light-gray or reddish crystals of felspar, which have in some 
cases rhomboidal, in others short-rectangular or irregular out- 
lines. One of these dykes (1250 meters above the sea, on the 
west side of Mount Steenstrup) contains numerous fragments of 
sandstone, about the size of peas. The syenite-porphyry dykes 
hold their course for long distances and are frequently over ten 
meters in width. 
Quartz-porphyry dykes are not quite so common, they are 
from two to ten meters in width and their direction is N. E.- 
S. W. ог Е. М. E.-W. 5. W. The most frequent variety has 
a grayish-red or grayish-violet ground-mass of dense or ex- 
tremely fine-grained structure; as phenocrysts occur both felspar 
(broad, rectangular sections, 3—8 millimeters in length) and 
quartz; the latter is in well-developed crystals of 1—2 milli- 
meters in length. This type was met with on the plateau west of 
the mountain Hatten and on the west side of Mount Steenstrup. 
In several of the quartz-porphyry dykes the ground-mass is 
crowded with dark dots of the size of a pin’s head, which 
proved to be spherulites on microscopical examination. A di- 
vergent variety of quartz-porphyry is common among the pebbles 
in the large alluvial fan of North Siorarsuit; it has the same 
colour and general habit as the Ilimausak porphyry, but differs 
