112 



be indeterminable. The contact is a sharp, clean-cut line 

 showing no blending of the two rocks, and above is a 

 coarse-grained crystalline limestone. 



Apophyses from the granodiorite into the roof are of the 

 same character as the contact zone. They are very 

 silicious quartz porphyries, which, a few hundred feet from 

 the contact, become quartz veins. 



Interior Plateau. 



From the upper terminal of the Hedley Gold Mining 

 Company's gravity tramway, at an elevation of 5,400 feet 

 (1,646 m.) above sea level, an excellent view of the Interior 

 Plateau is obtained looking west. The plateau seen from 

 this point is merely a bay at the southern end, lying be- 

 tween the Okanagan range on the east and the Hozameen 

 range on the west, with the Princeton depression in its 

 central part. The main extent of the plateau is towards 

 the north, in which direction it stretches, with a width of 

 about 100 miles (160 km.) far into the northern interior of 

 British Columbia. 



Considerable doubt still exists relative to the history and 

 development of the characteristic features of the Interior 

 Plateau region. A maturity of relief and an evenness of 

 skyline, probably not amounting to actual peneplanation, 

 are believed to have been produced by subaerial erosion 

 acting throughout Eocene times. To some extent, at 

 least, these features have been preserved in the present 

 topography of the region ; and although much of the region 

 has undergone considerable disturbance by mountain 

 building forces and vulcanism, in the succeeding periods, 

 local irregularities of the surface produced at such periods 

 were again reduced by erosion in the quiescent periods 

 following them, especially in early Pliocene. Since, there- 

 fore, the Interior Plateau region has been subject to erosive 

 action throughout the whole of Tertiary times, its present 

 physiographic characteristics should be considered as the 

 cumulative result of that long period of time, rather than 

 of any single period of the Tertiary. There is no doubt 

 that at a time immediately preceding the Pliocene uplift 

 the vertical relief in the region must have been fairly low 

 and the maturity of form much more pronounced than at 

 the present time. The Pliocene uplift is estimated to have 

 elevated this region about 2,500 feet (762 m.) higher above 

 sea-level than its pre-Pliocene level, and the deep trough- 



