2l6 



Kilometres. ^ passes, by interbedding, into the "basal 

 quartzite." (See p. 133). 



The unconformity is here not marked by a 

 conglomerate but by a fine-grained feldspathic 

 sandstone, very similar in appearance to the 

 altered orthogneiss beneath. The basal quart- 

 zite is interpreted as a statically (and dynami- 

 cally?) metamorphosed arkose sand derived 

 from the adjacent orthogneiss and washed but 

 a short average distance from the parent, 

 pre-Beltian ledges. It is practically impossible 

 to indicate the exact plane of the unconformity, 

 but it may be approximately located at the 

 horizon where aplitic dykes cutting the ortho- 

 gneiss cease to be visible in the quartzitic 

 rock. The uncertainty is partly due to the 

 intense static metamorphism of older and 

 younger rocks alike; partly, to the deep 

 weathering of the orthogneiss before it was 

 covered by the bedded arkose. Microscopic 

 study shows that, for depths of 60 to 75 metres 

 stratigraphically below the surface of uncon- 

 formity, the orthogneiss has been thoroughly 

 altered. This alteration is apparently only 

 explicable as due to profound secular weathering 

 preceding deep-burial metamorphism. 



Opportunity will be afforded for a more 

 extended study of the orthogneiss itself. It 

 has the form and relations of a broad laccolith or 

 sill, with a thickness of 1000 metres for the part 

 still remaining after the Beltian erosion. Along 

 the railway the mass can be well seen to show 

 a persistent gneissic structure which is closely 

 parallel to the bedding and fissility of the over- 

 lying Beltian strata. The lower contact of 

 the sill crosses the railway at a point about 2000 

 metres west of Albert Canyon station. There the 

 ancient granitic magma was clearly intruded 

 along a plane parallel to the banding in dark 

 schists probably in part of sedimentary origin. 

 These bedded Shuswap rocks and the great 

 intrusive sheet evidently lay nearly horizontal 

 while the Beltian strata were being deposited 

 upon them. Their flat position was typical 



