38 
MUSEUM BULLETIN NO. 30. 
Applying these criteria to the East Sooke gabbro, it is 
found that although the feldspars in every hand specimen exhibit 
variations in composition, nevertheless in most of the rocks they 
are far from exhibiting maximal zoning. The feldspars of only 
a few of the coarse, pegmatitic varieties are noticeably zoned. 
Hence it must be concluded that considerable undercooling took 
place, in spite of the fact that the cooling of such a large plutonic 
mass was almost certainly fairly slow. In support of this con- 
clusion there might also be cited the uniform composition of all 
of the minerals throughout a large part of the gabbro. 
Furthermore, th$ occurrence of poikilitic textures in some of the 
rocks indicates a very rapid growth of the pyroxene crystals once 
crystallization was initiated. The rather imperfect segregation 
of the different minerals in the more basic rocks, as evidenced 
in the lack of occurrence of highly basic types such as pyroxenite, 
dunite, and picrite, and the incomplete segregation of the anorth- 
osites, also points to a crystallization deferred until increasing 
viscosity was almost able to prevent the downward movement of 
crystals. The fact that so much differentiation actually did take 
place, in spite ‘.of the relative brevity of the period between the 
commencement of crystallization and the time when viscosity 
ended the downward movement of crystals, throws an interesting 
light on the speed with which sinking, once initiated, may go on. 
FINAL STAGES OF DIFFERENTIATION. 
During the final stages of the differentiation of the Sooke 
magma the hornblendite and aplite veins were formed. The pro- 
cesses of deposition and the behaviour of the components of the 
solution have been so different from that displayed during the 
crystallization of the original, magma as to be worthy of separate 
detailed description. The mineralogy of the veins, their con- 
nexion with the gabbro mass, and their metamorphic effect on the 
gabbro have been detailed on pages 12-16 and shown by analyses 
on page 18, and the results of these analyses have been platted 
graphically in Figure 1. 
