REPORT OF THE CHIEF ASTRONOMER 445 



SESSIONAL PAPER No. 25a 



In the Norm classification the rock is the dosodic yellowstonose of- the 

 alkalicalcic rang, coloradase, in the persalane order, britannare. According to 

 the older classification the rock enters the class of quartz-mica diorites but 

 verges on typical granodiorite. 



Seven other specimens of the batholith as exposed to the westward of the 

 Ashnola gabbro were studied microscopically. They were found to include yet 

 more basic diorites and also types which belong to the biotite granites rich in 

 plagioclase. The specific gravities of the seven specimens range from 2-644 to 

 2-775, averaging 2-706. 



Where strong shear-zones occur in the Western phase they are occupied by 

 dark greenish-gray, fine-grained, fissile hornblende gneiss very rich in horn- 

 blende and similar to the metamorphic filling of shear zones in the Osoyoos 

 granodiorite. Between these narrow shear zones the more normal rock iisually 

 shows mechanical granulation and fracture rather than extensive recrystalliza- 

 tion. 



Roughly estimating the relative volume of each type, the writer has con- 

 cluded that the Western phase is, on the average, a granodiorite which is very 

 •close to a quartz diorite. At the western side of the exposed batholith where it 

 disappears beneath Cretaceous sediments, the granitic rock is relatively un- 

 •crushed, poor in orthoclase and rather abundantly charged with phenocrystic 

 biotite and with hornblende. Toward Park mountain the zones of intense 

 shearing become more and more numerous. The rock then loses its porphyritic 

 appearance and tends to be a gneissic biotite granite, in which hornblende is 

 wanting and orthoclase has increased at the expense of the soda-lime feldspar. 

 Near the long band of Ashnola gabbro the Western phase carries bands of 

 ■crushed rock which is indistinguishable from the staple rock of the Eastern 

 phase. 



Eastern Phase. — East of the roof-pendant of Ashnola gabbro the batholith 

 shows evidence of having undergone its maximum shearing and metamorphism. 

 It there consists of narrow bands of highly micaceous gneiss alternating with 

 parallel, much broader bands of less micaceous gneiss. These bands are generally 

 more acid than the typical rock of the Western phase. 



A specimen fairly representing the average of the Eastern phase was collect- 

 ed at a ledge 1-8 miles south of the Boundary line and in the middle of the 

 zone of the batholith composed of this phase (Figure 32). The rock is in macro- 

 scopic appearance a light gray, medium-grained, somewhat gneissic granite, 

 weathering light brown. Quartz, biotite, orthoclase, and plagioclase (probably 

 andesine, near Ab, An,) are the essential components. Rare apatite, zircon, 

 and magnetite grains are the accessories. A few reddish garnets are occasion- 

 ally developed. There is seldom any indication of straining or crushing of the 

 minerals constituting the band whence the specimen was taken. Microscopic 

 study leaves the impression that the material of this and similar bands has been 

 wholly recrystallized. The structure is now the hypidiomorphic-granular. 



This specimen (No. 1398) was analyzed by Mr. Connor with result as 

 follows : 



