REPORT OF THE CHIEF ASTRONOMER 439 



SESSIONAL PAPER No. 25a 



The dike-rock may be classed as a hornblende-bearing harzburgite. The 

 specific gravity of a large, relatively fresh specimen is 3-099. 



Vesicular Andesite Dikes. — On the 7,718-foot summit north of Peeve Pass 

 a half-dozen andesite dikes, varying from a foot to six feet or more in width, 

 cut the Basic Complex. These dikes are nearly vertical and strike between N. 

 45° E. and !N" 90° E. All of them are more or less vesicular. The material of 

 the dikes seems to be uniform — a rather light gray, amygdaloidal lava, either 

 aphanitic or porphyritic, with phenocrysts of altered plagioclase (probably 

 labradorite) and of augite. The ground-mass is a felt of minute plagioclase 

 microlites, largely chloritized augite granules, and abundant glass. The rock 

 is almost certainly an augite andesite and in any case must vary but little from 

 that common type. The amygdules are composed of calcite ; like the phenocrysts 

 they are generally arranged parallel to the dike-walls. This arrangement is 

 probably a flow-structure and is not due to crush-metamorphism. In fact, the 

 lava-like rock does not seem to have been appreciably squeezed at all. 



The field evidence thus went to show that the andesite was intruded after 

 the wholesale shearing of the Complex had taken place. A vesicular dike of 

 olivine basalt cuts the Cathedral granite. It is probable that the andesite dikes 

 were injected very late in the history of the composite batholith. In both cases 

 the vesicularity of the dike-rocks suggests that they were intruded near the 

 surface; if so, they belong to the Recent period or to the latest Tertiary. 



Osoyoos Batholith. 



That part of the Okanagan valley in which Osoyoos lake lies has been 

 largely excavated in a body of intrusive, granitic rock to which the name 

 ' Osoyoos batholith ' has been given. The northern and southern limits of the 

 body were not determined but they are known to occur well outside the Boundary 

 belt. (Plate 38). 



Original Granodioritic Type. — The batholith has undergone such drastic 

 alteration through dynamic metamorphism that it is difficult to find ledges or 

 oven hand-specimens of the original rock. Considerable sampling of the mass 

 within the five-mile belt has led the writer to conclude that, while the body was 

 of distinctly variable composition at the time of its crystallization from the 

 magma, yet that the staple or dominant rock was originally a rather typical, 

 medium- to coarse-grained granodiorite. 



The colour is the familiar light gray characteristic of monzonites, grano- 

 diorites, and some other granular rocks rich in plagioclase. In the likewise 

 fresh though somewhat metamorphosed phases the rock assumes a light greenish- 

 gray tint due to the dissemination of metamorphic biotite or to the abundant 

 development of epidote. All phases weather light brownish-gray. The essential 

 •constituents are deep green hornblende, brownish-green biotite, orthoclase, 

 quartz, and unzoned andesine, Ab 3 An,. The accessory minerals are apatite, 

 zircon, magnetite, and titanite; none of these may be called abundant. Allanite 

 in rather large amount is accessory in the basified contact zone. Colourless 

 epidote is invariably present, but is regarded as of metamorphic origin. Where 



