90 
A brief description may be given of the macroscopic ap- 
pearance of the main types with notes on their occurrences. 
The diabases of Ilimausak are much like those of Nuna- 
sarnausak (p. 56). A dense, dark-gray diabase, rich in secon- 
dary epidote, was found north of Tunuarmiut, at a height of 
about 300 meters. Other varieties with fine-grained or medium- 
grained structure make up the uppermost part of Mount Steen- 
strup; these varieties are unusually rich in large, macroscopic 
grains of magnetite and needies of apatite; they have been very 
intensely modified by contact-metamorphism and are filled with 
flakes of a brown biotite. The exceptional intensity of the 
contact-metamorphism here is doubtless connected with the 
fact, that the mountain is traversed by very numerous dykes of 
arfvedsonite granite. 
The porphyrites are the most widely distributed rocks of 
the whole series. They have a dense, greatly altered ground- 
mass of dark brownish, greenish or grayish-violet colour. The 
felspar phenocrysts show twin-striation; they are of a thin 
tabular form, usually /2—1!/2 millimeter thick and 15—25 milli- 
meters long. As a rule they show a well pronounced fluxional 
arrangement. 
The porphyrites have been observed as sheets at the fol- 
lowing places: on the mountain 760 meters high south-west of 
Tasek; on Nunasarnak above the nepheline-syenites; at Tunu- 
armiut; at a height of 800 meters above ‘Tunuarmiut; on the 
west side of Mount Steenstrup at heights of 1000 meters and 
1140 meters; at a height of about 750 meters on the unnamed 
mountain lying to the west of Mount Steenstrup. 
The name ‘“llimausak porphyries” may be given to a num- 
ber of porphyries, probably effusive, which are found especially 
in the highest parts of the series and form a well-defined group 
in their macroscopic appearance. Their ground-mass is abso- 
lutely dense and of a dark bluish-black or brownish-black col- 
our; it contains felspar phenocrysts to a varying amount. The 
