94 



The river connecting the two lakes is rather more than a 

 mile (i -6 km.) in width, bordered by flat bottom lands and 

 low terraces. This portion of the valley must represent 

 an ancient and deep hollow filled in by glacial drift and 

 later deposits. At present considerable sedimentation 

 is being effected by the material carried down by the 

 tributary streams. 



GENERAL GEOLOGY [8]. 



The geology of the valley sides and neighbouring mountain 

 ranges has not been worked up in any detail and at present 

 only permits of a very generalized description. From 

 Castlegar to a point about south of Saddle peak the valley 

 is eroded in rocks of two batholithic intrusions, the earlier 

 being the Nelson granodiorite of Jurassic (?) age, and the 

 later the Rossland alkali granitic rocks tentatively referred 

 to early Tertiary. The former extends from Castlegar 

 to near Deer Park and then again from a point three miles 

 (4-8 km.) south of the Needles to the bend in the Columbia 

 river. The latter extends from Shields to a point three 

 miles (4-8 km.) south of the Needles and occupies for the 

 most part both shores of the lake. Of irregular lenticular 

 form the batholith is 38 miles (61 km.) in length along its 

 north axis with a maximum width of 17 miles (27 km.). 

 Lying in these batholiths are a few remnants of the Rossland 

 group with some associated limestone developed along the 

 lower portions of Lower Arrow lake particularly in the 

 vicinity of Deer Park. 



South of Saddle peak a band of schists and gneisses 

 presumably of the Shuswap series crosses the valley with a 

 trend a little west of north. 



Little is definitely known of the shores of Upper Arrow 

 lake as far as Halcyon. The rocks are schists, gneisses, 

 slates and crystalline limestones intruded by dykes, sills 

 and stocks of late granites, etc. They may be referred to 

 the Shuswap and Selkirk series together with highly 

 metamorphosed phases of the Slocan series. They are 

 much disturbed and faulted requiring detailed work to 

 elucidate their structure. 



From Halcyon to Arrowhead the Shuswap terrane is 

 developed except at Thumb bay where the continuity is 

 broken by an intrusion of granite some five miles (8 km.) 

 wide which crosses the lake with a northwest trend. 



