170 
as an exceedingly fine-grained variety of ægirine-lujavrite: in 
the contact-modification the ægirine-needles reach a length of 
not more than 0:2 millimeters. In the specimens examined the 
light-coloured minerals are entirely replaced by analcime, but 
the contours of the original crystals of felspar and nepheline 
are clearly indicated by the arrangement of the egirine-needles. 
Contact phenomena of ‘another kind pointing to a much 
slower rate of cooling are seen at the eastern boundary of the 
lujavrite, between Agpat and Kitdlavat. Here the egirine- 
lujavrite borders upon Algonkian granite, the contact-plane is 
vertical, and the size of grain is seen to keep constant or even 
to increase on approaching the granite. Nearest to the contact 
the lujavrite is traversed by a large number of pegmatitic veins. 
Arfvedsonite-lujavrite. 
This rock appears dark grayish-black; it has a moderately 
fine grain and a somewhat schistose structure. With the naked 
eye or with the lens it is seen to consist of arfvedsonite, 
felspar, nepheline, and eudialyte. The arfvedsonite is the chief 
constituent and occurs in small glittering black needles or 
prisms arranged parallel to the schistose structure. The light- 
coloured minerals are of the same general habit as in the 
ægirine-lujavrite. In contradistinetion from the latter rock the 
arfvedsonite-lujavrite is tolerably even-grained and never shows 
a porphyritic or pseudo-porphyritic appearance. 
Microscopic characters. — Under the microscope the main 
constituents are seen to be arfvedsonite, microcline, albite, 
nepheline, and eudialyte. Ægirine and sodalite are present in 
some specimens but in others one of these minerals or both 
may he entirely absent. Locally analcime is very abundant as 
a secondary product replacing felspar and nepheline, not un- 
frequently spreustein is also present. The number of occasional 
accessories is considerably greater than in the egirine-lujavrite ; 
they will be mentioned below. 
