12 
MUSEUM BULLETIN NO. 30. 
present, indicating that water was being concentrated in these 
acid magmas, but not necessarily in large amount. The total fer- 
romagnesian mineral may amount to 40 or 45 per cent in the 
more basic types, but rapidly decreases with increasing acidity, 
until in the very siliceous dykes there is less than 5 per cent. 
Titanium, which in the ordinary gabbros is always combined 
with iron as titaniferous magnetite, in the granite dykes always 
takes the form of titanite. Only five of the granite dykes weie 
found, confined to the Rocky Point mass. This fact, coupled 
with the petrographic resemblance to the granites of East Sooke 
and other bodies, strongly suggests that the dykes are the grani- 
tic differentiate which in this mass has been forced into more 
definitely intrusive relations with the gabbro than in the other 
bodies. 
4 
The sequence of irruption of the dykes has not been deter- 
mined satisfactorily owing to lack of sufficient data. Only in 
two cases were dykes observed to cut one another. On Rentinck 
island a dyke of the granitic type cuts one of the non-porphyritic 
gabbroid type. On Possession point a dyke of the porphyritic 
gabbroid type cuts the intrusive granitic differentiate. Assum- 
ing the equivalence of the granite of Possession point with the 
granite dykes of Rocky point, the sequence is as follows : 
Porphyritic gabbroid dykes 
Granite and granitic dykes 
Non-porphyritic gabbroid dykes 
Olivine and augite gabbros. 
Veins. ’ 
Hornblendite Veins. The hornblendite veins are replace- 
ment veins formed by the action on the gabbro of solutions rich 
in iron and magnesia rising through joint cracks and 
other fissures. The majority of the veins are only a few inches 
in width, but some are very large, 50 to 250 feet wide. Like 
most replacement veins, they are characterized by great variabil- 
ity in width along their strike, and have no clean and definite 
vein wall, but grade into the unaltered wall rock. Under the 
v microscope, the replacement of the various constituents of the 
