2 
MUSEUM BULLETIN NO, 30 . 
The writer wishes to express his thanks to C. H. Clapp for 
aid in the field and information freely supplied as to results 
obtained in the study of the other stocks of the Sooke gabbro 
which the writer ^as unable to examine ; and to W. H. Collins 
and G, A, Young, of the Geological Survey staff, for many 
helpful suggestions and much critical discussion of this paper. 
GENERAL GEOLOGY. 
The principal formation of the peninsula is the Sooke gab- 
bro. The nature of the mass, whether stock or laccolith, is * 
unknown , 1 since bedding is difficult to determine in the basalt 
flows into which the gabbro is intrusive, and since She roof has 
been so completely removed that no foreign rock now occurs 
within the gabbro area, and the older basalts are present only in 
small, isolated patches along the shore. 
The gabbro intrudes the Metchosin basalts of upper Eocene 
age , 2 and is, therefore, post-Eocene. It is overlain on Sooke 
peninsula by the Sooke formation, a series of slightly consoli- 
dated sandstones and conglomerates underlying a small area on 
the southeast coast and filling isolated wave-cut chasms on the 
south coast. These sediments were determined from their 
fossils to be of early Miocene age, or possibly middle or upper 
1A conjecture may be hazarded as. to the nature of the intrusive masses 'from a 
knowledge of the amount of granitic differentiate present. F. E. Wright in his study 
of the gabbro mass of mount Bohemia (Mich, State Board Geol, Surv., Rept. 1908, p. 
355) calculated from field evidence that the amount of aplitic differentiate was about 
17 per cent of the whole mass. W, H. Collins has estimated that aplitic material 
formed approximately 12 per cent of the Gowganda diabase (Geol. Surv., Can., Mem. 
33, p. 75). Clapp, when examining the Sooke gabbro masses, observed in the case of 
the Empress Mountain body, which has not been disturbed during consolidation, that 
the granitic differentiate formed a layer 100 feet thick at its summit. Assuming 
that this is the whole of the granitic differentiate, the gabbro is determined to have 
a maximum thickness of 800 feet, using Collins' figures. Assuming that segregations 
has been imperfect and that total amount of granitic differentiate is double that 
collected at the top; and in addition that in these gabbros the granite is only 5 per 
cent of the total mass instead of 12 per cent, the body is 4,000 feet thick as a maxi- 
mum. The Empress Mountain mass is 6 miles long by 3 miles wide; - its shape 
would, therefore, appear to be laccolithic rather than stock-like. Unfortunately 
none of the other masses in the Sooke majJ-area afforded data of this kind. 
2 Clapp, C. H., Geol, Surv., Can., Sum. Rept. 1912, p. 48. 
