GABBROS OF EAST SOOKE AND ROCKY POINT. 
29 
THEORETICAL PART. 
INTRODUCTORY STATEMENT. 
The facts detailed in the preceding pages have shown that 
the Sooke intrusives include a large number of different petro- 
graphic types that fall naturally into a series of which, although 
the end members are widely different, the proximate members 
differ but slightly. The writer will endeavour to prove that these 
differences are due to the process of differentiation acting on an 
originally homogeneous magma whose composition was probably 
that of a rather basic basalt. The different rock types present 
certain irregularities, previously detailed, of distribution, shape, 
and inter-relations with one another; it will be shown that the 
most likely explanation of these irregularities is the occurrence of 
movement and disturbance within the masses prior to their 
consolidation. It is possible that the movements may have been 
those which accompanied the intrusion of the masses, in which 
case the differentiation must have taken place at greater depths ; 
but the bulk of the evidence seems' to indicate that they were not 
so profound as this would imply, and that the actual sequence of 
events was, intrusion, differentiation, and movement. The 
method by which the differentiation appears to have taken place is 
that of partial crystallization and sinking of crystals, aided in 
the later stages by the regional movements, which strained off 
or squeezed out the mother liquor from partly crystallized 
material. Bowen 1 has recently shown that such an explanation 
of differentiation appears the only adequate and possible one; 
and the facts observed in the study of the Sooke intrusives bear 
out his theory. The records of the final stage of differentiation, 
the period of exhalation of aqueo-igneous solutions, are here 
unusually complete, for there have been two types of veins 
formed by these solutions, a basic and an aplitic, instead of only 
the usual aplitic veins. Unfortunately, owing to the smallness 
of the intrusive mass, cooling and consolidation overtook "and 
ended the differentiative processes before their work was com- 
plete. 
i Bowen, N. L., Jour, of Geol., supplement to vol. 23, 1915. 
