39 
The rock through which the stringer cuts consists of some 50 per cent 
of coarse crystals of aegirine-augite, very near to aegirine in composition, 
as determined by the large extinction angle, set in a matrix of well-crystal- 
lized microperthite, albite, and a little quartz. Biotite, magnetite, and 
very coarse grains of apatite also occur. In the hand specimens, brown 
crystals of titanite are easily discernible. In the thin section most of the 
latter are altered to a mass of leucoxene (?) — yellowish and practically 
isotropic — and calcite, with clear crystals of albite within them. 
The original aegirine-augite is altered, near the stringers, to a fibrous 
mass of blue or green amphibole whose extinction angle increases from 
essentially 0° in the blue to violet varieties to 35° ± in the green varieties. 
The j3 index of the greenish amphibole was determined as 1-670 ± 0-003. 
It seems that all varieties between the green and the blue to violet amphi- 
boles result from the alteration of aegirine-augite. The amphiboles may 
replace the pyroxenes very irregularly in shred-like manner or they may 
perfectly preserve the original crystal form of the pyroxenes. Some crystals 
of the aegirine-augite show, especially on acute corners in basal section, 
areas of the deep blue amphibole which reach a position of extinction at 
the same moment as the original pyroxene and are likewise basal sections. 
Amphibole, in shreds, also cuts across large and small grains of feldspar 
and is distinctly later than this mineral. This is a striking example of the 
conversion of pyroxene to amphibole and in view of the large amount of 
blue amphibole, the alteration seems to necessitate the introduction of 
soda, although it is possible that sufficient quantities of that element were 
supplied by the original aegirine-augite. 
One of the most interesting thin sections shows a trachytic, dark green, 
syenite porphyry cut by a one-half inch, greyish green, fine-grained dyke. 
The older rock consists of coarse crystals of feldspar, principally orthoclase 
and microcline, with a large proportion of aegirine-augite and biotite. 
These components are now badly altered. 
The greenish dyke is of a fine-grained, holocrystalline mass of albite, 
microcline, and orthoclase, the latter two being very minor in quantity. 
These are cut by shreds of blue to green amphibole which, in some cases 
at least, have resulted from the alteration of tiny needles of aegirine that 
is very sparingly present. Considerable apatite, titanite, and magnetite 
or ilmenite are present throughout the section. The pyroxene has been 
largely converted to amphibole and the latter has also developed abun- 
dantly throughout the feldspar. This conversion is most pronounced along 
the edge of the light-coloured dyke. Numerous varieties of amphibole 
occur. A green variety, when examined, was found to have a maximum 
index of 1 -65 -K It is biaxial, negative, has an optic angle of medium size, 
and its extinction approximates 18 degrees, evidently representing a stage 
intermediate between the blue-violet and dark green varieties described 
above. 
On the western edge of the intrusive mass, just north of a small hut 
on the “Chance” claims, a considerable area of dark, fine-grained rock occurs. 
It consists of well-crystallized, green to colourless prisms of augite with 
extinction up to 52 degrees, set in a somewhat finer-grained mass of ortho- 
clase and albite. An important amount of green biotite, containing numer- 
ous microscopic needles of rutile(?), is present. Magnetite or ilmenite, 
titanite, and apatite are quite abundant and epidote has formed by altera- 
tion of pyroxene. 
