46 
MUSEUM BULLETIN NO. 30. 
age. Its resemblances in composition to the Metchosin basalts, 
and the restriction of its occurrence to the areas underlain by 
them, strongly suggest the view that represents the plutonic 
phase of the igneous cycle that began with the extrusion of the 
basalts in late Eocene times. The masses examined by, the 
writer were those underlying East Sooke peninsula and Rocky 
point. The oth$r gabbros of the Sooke map-area were studied 
by C. H. Clapp; and present certain differences which may be 
summarized as the results of quieter, less disturbed crystalliza- 
tion. 
The intrusion of the gabbro seems to have taken place 
quietly, as it has not formed extensive shatter breccias at its 
contacts. Cooling then began, and evidence has been given to 
show that a considerable degree of undercooling probably took 
place before crystallization was initiated. When the crystals 
began to form, they coincidently began to sink through the liquid 
magma, on account of their greater specific gravity, and thus 
caused the separation of the originally homogeneous magma into 
several portions of differing composition, the lighter of which 
occupied the upper horizons. This primary differentiative pro- 
cess was not long continued, however, and did not result in any 
very perfect sorting of the various rock minerals, as it was 
brought to an end at an early date by the increasing viscosity 
of the cooling liquid. It resulted, however, in the production of 
four different rock types, of definitely different mineral com- 
position; and each type groups together a series of rocks whose 
end members differ widely in composition, but of which any two 
adjacent members differ only slightly. Even the classification 
into four general types is a more or less arbitrary one, since, as 
might be expected from rocks so formed, the different types 
merge into one another by a gradual change in mineral composi- 
tion. 
The types so formed are : olivine gabbro, made up of olivine, 
pyroxene, and bytownite feldspar; augite gabbro, similar to the 
preceding but without olivine; anorthosite, consisting of by- 
townite feldspar either pure or containing small quantities of 
pyroxene with or without olivine; and granite, made up of 
