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The potash-felspar, when clear, is seen to be microcline with 
a fine-grained twin-structure but, when turbid, it looks like 
orthoclase. In some specimens of quartz-porphyry the felspar- 
phenochrysts seem to be soda-orthoclase with only a few and 
small veinlets of albite perhaps of secondary origin. 
The guartz-phenocrysts are sometimes sharp edged crystals, 
sometimes they are more or less corroded in the usual way. 
They contain fluid-pores and included portions of the ground- 
mass. Phenocrysts of ferromagnesian minerals now quite con- 
verted into iron oxides have been found in a few cases. They 
have the shape of long prisms and have perhaps originally con- 
sisted of soda-amphibole. 
The ground-mass* is micro-granitic or micro-pegmatitic. 
When tolerably unaltered it consists of potash-felspar, quartz, 
and a blue amphibole. 
Among the specimens collected the least altered comes 
from a heavy dyke in the sandstone on the south coast of the 
Sermilik Fjord just below Mount Steenstrup. In this specimen 
the ground-mass is microgranitic, but small areas of micro- 
graphic intergrown felspar and quartz are seen with tolerable 
frequency in the slices. The size of the grain of the ground- 
mass is 0'05—0"2 millimeter. The quartz is very abundant and 
shows some tendency to crystallographic outlines. The felspar 
is in broad and short laths or grains. It is a microcline- 
microperthite. The blue amphibole is in small allotriomorphic 
anhedra which are mostly elongated parallel to the vertical 
axis. The extinction-angle с:а is small but cannot be deter- 
mined with exactness; the absorption-tint for a and 6 is a dark 
grayish blue, for c a light grayish green. The mineral is thus 
probably a riebeckite. 
Another specimen from a dyke in porphyrite 5 meters 
wide and from a locality east of the summit of the Ilimausak 
and about 830 meters above sea level, has almost the same 
structure but is more altered. There is no blue amphibole but 
