464 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



granite, is the other pole of the differentiation. The chief difficulty of discuss- 

 ing this view, as of all its competitors, lies in the limited nature of the data 

 from the structural geology of the range. Herein lies the importance of a com- 

 parison with the magmatic history of the Purcell sills and analogous injections 

 of which the structural relations are well understood. Such comparison will 

 be noted in the theoretical chapter XXVII. 



Dikes Cutting the Cathedral Batholith. — Near the highest peak on Bauer- 

 man ridge the coarse Cathedral granite is cut by a small dike of typical olivine 

 basalt. The dike is exposed for sixty feet, in which distance it varies in width 

 from four feet near the middle of the exposure to less than two feet at each 

 end. The basalt thus forms a lenticular mass, standing practically vertical. 

 The strike of the dike is ~N. 35° E. and in the same quadrant as the average 

 strike of the andesite dikes cutting the Basic Complex. The basalt is even 

 more vesicular than the andesite mentioned. The middle of the dike is abund- 

 antly charged with gas-pores one to three millimetres or more in diameter. 

 These are commonly elongated parallel to the walls of the dike. For five or ten 

 centimetres from each wall the pores are very rare and the rock is compact, as 

 if by chilling. The basalt carries xenoliths of the adjacent granite and of large 

 quartz and feldspar crystal fragments also torn from the walls. 



The microscope shows that the basalt is exceedingly fresh, not even the 

 olivine being essentially affected by weathering. In view of this freshness it is 

 noteworthy that the vesicles carry no trace of calcitic or other filling. It looks 

 as if they had never been filled with mineral matter. These facts together with 

 the vesicular character of the lava, suggest that the basalt was injected near the 

 surface and is therefore of later date than the unroofing of the batholith. In 

 any case it is the youngest eruptive known to occur within the Okanagan 

 composite batholith. 



The phenocrysts are greenish augite and colourless olivine, both of which 

 gre abundant. The ground-mass consists of bytownite laths and augite granules, 

 with a mesostasis of brown glass. 



Two small, parallel, lamprophyric dikes of pod-like form and less than three 

 feet in maximum width, cut the Cathedral granite on the ridge 1,200 yards 

 northeast of Cathedral Peak. These dikes, in contrast with the basalt, are much 

 altered and it is difficult to diagnose them. The original constituents seem to 

 have been plagioclase, green hornblende, diopsidic augite, and possibly some 

 biotite. The grain is fine; the structure, panidiomorphic to eugranitic. The 

 rock may be a greatly altered camptonite or else hornblende diabase. 



Park Granite Stock. 



The Park granite stock measures 4 miles in length by 2J miles in width 

 (Figure 33). This granite is coarse, unsqueezed, and in almost all respects 

 resembles macroscopically the Older phase of the Cathedral batholith, of which 

 the Park granite seems to be a satellite. Under the microscope the rock differs 

 from the coarser Cathedral granite chiefly in the entire replacement of micro- 



