188 
The felspar of the typical augite-syenite is a soda-orthoclase. 
The grains show traces of crystallographic development where 
they touch augite, hornblende, nepheline, or quartz, but as a 
rule they are of quite irregular form. The maximum diameter 
is mostly only 2 or 3 millimeters. The extinction angle in 
sections perpendicular to the obtuse bisectrix (and thus parallel 
to (010)) is about 12°. In the same sections the homogeneity 
is often broken by narrow bands of microperthitic structure 
extended about parallel to the vertical axis!. Other felspar- 
grains in the same slices show a more or less plain crypto- 
or microperthitic structure throughout, with the orthoclase and 
plagioclase areas quite irregularly dispersed in dots or patches. 
The latter seem to belong to an oligoclase-albite. A closer 
inspection is rendered difficult by the felspars being usually 
rather weathered. The degree of weathering seems to bear a 
certain proportion to the degree of differentiation which the 
felspars have undergone: the fresher the felspars, the more the 
structure approaches the homogeneous soda-orthoclase. — In 
the variety of augite-syenite where the felspar-crystals show a 
tendency to the tabular shape, their dimensions are as a rule 
greater (length 1/2 to 1 centimeter) and the structure more va- 
riable: in some cases soda-orthoclase, in others chiefly crypto- 
perthite, in others again microperthite with fine and irregularly 
dotted structure or with a tendency to a banded structure pa- 
rallel to (801). 
Nepheline is only present in very scant degree in this rock 
so that in each slice only a few, rather weathered anhedra are 
seen filling angular interspaces between the felspars. In the 
specimens of augite-syenite with tabular felspar nepheline is as 
a rule quite absent. i 
Quartz is found sporadically in a few specimens of the 
coarse-grained augite-syenite and occurs abundantly in a contact- 
1 Described in Meddelelser om Grønland XIV (1894), р. 63 and table У, 
и 
