14 
MUSEUM BULLETIN NO, 30 . 
found during the course of the field work. One of these was 
observed on Bentinck island, a second and third on the Race 
rocks by the writer, and the fourth was found by his assistant, 
V. Dolmage, in the interior of East Sooke peninsula. These 
veins are characterized in three of the cases observed by a very 
basic edge, the width of which is about one-third that of the 
whole vein, grading into an aplitic centre. The composition of 
the edge in each case is that of a very coarse-grained basic gab- 
bro: 60 to 75 per cent of pyroxene approximately, the remain- 
der bytownite feldspar. From edge to centre a gradual decrease 
in the proportion of pyroxene takes place, with increase in the 
proportion and alkalinity of the feldspar, until near the centre 
the pyroxene alters to hornblende and becomes small in quantity, 
quartz begins to crystallize out, and the feldspar becomes oiigo- 
clase-albite, about Ab 90 An 1Q . The whole of the Bentinck Island 
vein is exceedingly coarse-grained and many of the crystals are 
more than an inch in diameter. The change from a basic edge 
to an aplitic centre is not nearly so marked as in the other veins, 
but nevertheless the change in composition is seen under the 
microscope to have been similar. The ferromagnesian mineral 
is hornblende, which may be primary or secondary ; the feldspars 
are zonally banded, with a kernel of composition Ab S0 An 70 , and 
outermost bands Ab S5 An 15 ; and, as the last product of crystalli- 
zation, some 5 per cent of quartz has been deposited in intersti- 
tial spaces. 
Aplite Veins . The aplites are found both as fissure fillings 
and as replacement veins and apophyses. The fissure fillings are 
rarely more than an inch or two in width, and commonly only a 
fraction of an inch, with clean-cut walls very slightly altered by 
the solutions. The alteration of the gabbro has been much more 
intense where the aplitic solutions have been forced through 
minute cracks and the intermineral spaces, instead of into open 
fissures. 
The aplite of the veins is equigranular, with an average 
grain of less than 1 mm., and is nearly pure white in colour. Free 
quartz is always present, and has been observed to constitute as 
