127 
but the latter figure may perhaps be erroneous as no attention 
was given to the difference between the foyaite and the sodalite- 
foyaite during the first part of the field work. 
Macroscopic appearance. — The outer habit of this rock 
is that of an ordinary coarse-grained foyaite with rather thin 
tabular felspar-crystals averaging 1 or 11/2 centimeters in length 
while the thickness seldom exceeds one-tenth of the length. 
The interspaces between the felspars are filled with a grayish, 
greenish, or reddish translucent nepheline and with black 
minerals. As a rule there is no law of arrangement of the 
felspar-crystals, sometimes, however, they show a very marked 
parallel disposition. Variations in size of grains are observed in 
some cases. 
Microscopie characters. — The main constituents of this 
rock are felspar, nepheline and a dark mineral which is com- 
monly egirine-augite but in some cases catophorite-like horn- 
blende. Subordinate constituents occurring in varying amounts, 
or sometimes wanting, are: sodalite, biotite, ægirine, arfved- 
sonite, ainigmatite, olivine, eudialyte. Apatite and iron ore 
are constantly present though in very small quantities. Cata- 
реше, cancrinite, spreustein, and analcime occur as secondary 
products. 
The apatite which occurs in small prisms is often enclosed 
in the felspar and in the nepheline, sometimes also associated 
with the dark minerals. The constant presence of apatite in 
this rock is noteworthy because apatite is absent or almost 
absent from all the other nepheline-syenites of Ilimausak. The 
tron ore is in rounded grains and occurs sparingly enclosed 
within the dark minerals. 
The felspar is in tabular crystals. It is a microperthite 
consisting of microcline and albite. The latter is present in 
somewhat greater amount than the microcline, and the outer 
boundary of the crystals is frequently pure albite. The micro- 
perthitic structure is of the same type as in the pulaskite 
