towards the remaining portion of the nepheline; in this sodalite 
no cleavage is visible, and its structure is probably fine-grained 
or spherulitic. ‘Thus, while the greater part of the sodalite in 
the naujaite has crystallized prior to the nepheline, sodalite in 
minor quantities has formed at the expense of nepheline both 
before and after the consolidation of the rock. This is in 
harmony with the well-known experiences in regard to the 
artificial production of sodalite’. Another less common altera- 
tion of the nepheline of this rock is the conversion to spreu- 
stein; this process is always posterior to the ‘sodalitisation’. 
In comparison with the crystals of sodalite and nepheline 
those of felspar are of gigantic dimensions: their length varies 
from 3 to 25 centimeters and averages about one decimeter. 
They are of thick tabular habit, the thickness amounting to 
about one fourth or one third of the length. Each felspar- 
crystal encloses a large number of sodalite-crystals poikilitically ; 
the cleavage surfaces for this reason are of a peculiar, coarsely 
dotted appearance. The clinopinacoidal crystal-faces (010) are 
well developed, sometimes also prismatic faces (110) are seen 
where the felspar is bounded by arfvedsonite. The crystals 
are very fresh, translucent, and of a light greenish or grayish 
colour. 
Under the microscope the felspar is seen to be a micro- 
cline-microperthite. The perthitic structure as well as the 
twin-structure of the microcline is very different from any of 
the ordinary types represented by the felspars of common gra- 
nitic and syenitic rocks, but both structures are of the same 
types as those characterizing the felspar of the sodalite-foyaite 
(see Fig. 14, р. 135). A still closer arrangement is found between 
the felspar of the naujaite and that of the pegmatitic veins. The 
latter has been described onja previous occasion”; the chemical 
analysis is here quoted: 
ТН. Возехвозсн, Mikroskopische Physiographie I, 2, p. 40 (1905). 
- Meddelelser om Grønland XIV, р. 21 and PI. I (1894). 
10° 
