REPORT OF THE CHIEF ASTRONOMER 297 



SESSIONAL PAPER No. 25a 



A typical specimen from this stock was studied' quantitatively according 

 to the Rosiwal method and the following weight percentages of the different 

 constituents were found : 



Quartz ?4 -9 



Microperthite 31-3 



Sodiferous orthoclase 15-9 



Oligoclase 12-1 



Biotite 3-8 



Muscovite -9 



Magnetite -9 



Apatite and zircon -2 



100-0 



Sp.gr 2-622 



Silica must form about 75 per cent of the rock. - 



The larger stock is surrounded by an irregular fringe of strong apophyses^ 

 some of which follow the trend of master joints in the invaded quartzites and 

 grits. A finely exposed 30-foot dike (mapped) of porphyritic biotite-granite 

 cutting the Wolf grit on the summit about 1,300 yards north of the Dewdney 

 trail, is probably an offshoot of the same magma. This dike runs east and 

 west with remarkable straigbtness and can be followed with the eye for nearly 

 two miles over the mountain slopes. It seems to lie in the prolongation of a 

 strong vertical thrust-fault which is marked on the map. 



A great number of other dikes occur in an unusually broad shatter-zone 

 occurring on the eastern and southern sides of the larger stock, where the 

 rocks of the Monk and Wolf formations are tremendously shattered for dis- 

 tances varying from 0-6 mile to 1-5 miles. Figure 20 illustrates the general 

 form and relations of stock and shatter-zone, which on the southeast is actually 

 broader than the stock itself. It is apparent in the figure that the bands of 

 the various invaded formations ,are not seriously disturbed from their regional 

 strike. The shattering has locally broken up each formation into a vast 

 number of fragments, but neither the Monk schist band, the Wolf grit band, 

 nor the Dewdney quartzite band has been driven out of alignment with the 

 unshattered portions -lying to north and south of the intrusions. The granite 

 of the main stock has evidently replaced an equal volume of the sediments. 

 There is no hint in the field-relations that the intrusion is of the laccolithic 

 or ' chonolithic ' order and thus due to a mere parting of the strata which per- 

 mitted of the ' hydrostatic ' injection into the opening so provided. The fact 

 that the granite was not intruded after the manner of a laccolith is further 

 demonstrated by the exceedingly strong contact metamorphism in the invaded 

 strata. 



Contact Metamorphism. — This exomorphic action is signally illustrated 

 throughout the shatter-zone to the southeast of the stock. (Figures 20 and 

 21.) For square miles together the Monk phyllites have, in that zone, been 



