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in its place small dots and irregular laps of black iron oxide. 
The felspars of the ground-mass are more clouded and consist 
of orthoclase-microperthite mixed with crystals of pure albite. 
A few small grains of zircon were observed, also a little 
fluorite. Of this rock a chemical analysis is given below. 
In a third specimen from the same locality as the last 
one, but from a dyke only two meters wide, the ground-mass 
has a micro-pegmatitic (granophyric) structure with a marked 
tendency to spherulitic arrangements. The dark minerals are 
completely converted into iron oxides and the whole ground- 
mass is finely dotted with black iron-ore. Somewhat similar 
is a specimen taken at a height of 800 meters in the talus at 
the foot of a peak east of Hatten, in this rock, however, the 
spherulitic structure is still more developed, the ground-mass 
consisting almost entirely of spherulites with a diameter of 
about one millimeter. The spherulites in this case contain not 
only felspar and quartz but also radiating needles of a mineral 
that has been completely converted into iron-ore. The sphe- 
rulites of this rock have therefore macroscopically the appear- 
ance of innumerable small dark spots in the ground-mass. 
A somewhat different type of quartz-porphyry is rather 
common among the blocks in the large alluvial fan at North 
Siorarsuit and must be supposed to be from one of the high 
Ilimausak peaks. This rock macroscopically resembles the Ili- 
mausak porphyry with the exception that its phenocrysts are 
both quartz and felspar. The quartz-phenocrysts have a sharply 
developed bipyramidal shape and the felspar-phenocrysts are 
microcline-microperthite. The ground-mass is bluish black and 
macroscopically looks homogeneous. Under the microscope it 
is seen to be full of small arfvedsonite-like prisms in tolerably 
parallel arrangement so that they produce a pronounced flow- 
structure. Their length varies about 0°05 millimeter, their thick- 
ness is only one tenth of this. The extinction-angle с:а is 
small, and the absorption-tints are those of the arfvedsonite, 
