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batholite. In most places where specimens have been collected 
the rock is not unlike the well known ‘‘foya type” although dif- 
fering in petrographic details. This rock which is probably the 
main rock of the batholite will be described here as the ,,Ko- 
rok type”. An essentially different type the ‘‘Usuk type” has 
been found in the valley east of Usuk. 
Korok type. 
Macroscopic appearance. — The foyaite of this type is a 
coarse-grained rock of a reddish-gray colour, less frequently 
brownish-red or gray. Among the thick tabular felspar crystals 
plenty of nepheline and dark-coloured minerals are to be seen. 
The felspar tables are of a very fresh, grayish appearance. On 
an average their thickness is 5 millimeters (varying from 1 to 
8 millimeters in the different places), and their widest extent 
which is parallel to the a-axis is from five to ten times as large 
as their thickness. Frequently they are arranged in parallels. 
The nepheline is reddish and of an elæolithic habit. It is in 
grains and in short prisms of a diameter of one quarter of a 
centimeter to a centimeter. It is just a little less idiomorphic than 
felspar. The dark-coloured minerals to be seen with the naked 
eye are a black pyroxene (ægirine-augite) and a black mica. 
In most places the foyaite is of a uniform size of grain. 
Considerable variations have only been observed in the western 
part of the foyaite area near the contact with the augite- 
syenite. Here both porphyritic and pegmatitic varieties are very 
common. The latter occur in veins and segregations of ir- 
regular form; locally they are extremely coarse-grained with 
felspar crystals which exceed half a meter in length. Rare 
minerals have not been found in these pegmatites. 
Microscopic characters. — Under the microscope the rock 
is seen to be made up of the following minerals: apatite, iron 
ore, egirine-augite, hornblende, biotite, felspar, nepheline, can- 
crinite, and alteration products (zeolites and calcite). Very small 
