115 
that is to say a granite in which arfvedsonite is largely predo- 
minant among the dark minerals — appear to be very uncom- 
mon rocks. As instances of closely related rocks may be cited 
the arfvedsonite-bearing soda-granites from the district south 
of Kongsberg in Norway as described by Brôccer (see analysis 
A in the above table), and those from Madagascar described by 
Lacroix". From a chemical point of view the arfvedsonite- 
granite of Ilimausak shows a close relation to the grorudites 
of many regions, and a somewhat less pronounced analogy to 
the Icelandic liparites and obsidians described by Bäcksıröm?. 
ARFVEDSONITE-GRANITE OF NARSAK. 
In the vicinity of Narsak arfvedsonite-granite covers three 
small areas separated from the arfvedsonite-granite of Ilimausak 
by a zone, 5 kilometers broad, of nepheline-syenites and por- 
phyrites. Although belonging to the western part of the 
igneous complex the Narsak granite will be described in this 
place on account of its near analogy to the Ilimausak rock. 
The arfvedsonite-granite of Narsak is a coarse- or medium- 
grained rock. As a rule it is of a strong red colour, locally 
also grayish white varieties are found. Under the microscope 
the main constituents are seen to be felspar, quartz, arfvedso- 
nite and egirine; apatite and magnetite commonly occur as 
minor accessories. The felspar is a perthitic microcline-albite 
of the same kind as that of the Ilimausak granite; as a rule it 
is somewhat more idiomorphic in the Narsak granite. Micro- 
pegmatitic intergrowths of felspar and quartz occur rather 
abundantly. The quartz is of the usual character. The prin- 
cipal difference from the Ilimausak granite appears in the 
dark-coloured minerals: in the Narsak granite no ainigmatite 
has been found and the arfvedsonite is accompanied by a 
1 A. Lacroix, Matériaux pour la minéralogie de Madagascar. Nouvelles 
Archives du Museum (4) I, p. 82, Paris 1902. 
> Geologiska Foreningens i Stockholm Förhandlingar, XIII, 1891. 
