REPORT OF THE CHIEF ASTRONOMER 277 



SESSIONAL PAPER No. 25a 



for even in its upsetting, the future observer's eye will be sharpened for the 

 essential facts. 



Summary on the Structure of the Nelson Range. 



The structural geology of the Nelson range -where crossed by the ten-mile 

 belt naturally involves a study of three different types of areal geology, corres- 

 ponding respectively to the Priest River terrane, the rocks of the Summit series, 

 and the large bodies of batholithic granite. 



The obscurity of relations among the old sediments of the Priest River 

 terrane has been described in the account of the different zones (belts) of the 

 terrane. Schistosity and bedding often coincide. Both sets of planes are 

 highly inclined, with dips averaging about 75° to the eastward. Quite vertical 

 dips are very common in the southern half of the belt. In the northern half 

 the Priest River rocks have been intensely crumpled by the intrusion of the 

 Bayonne batholith, giving local dips at all angles and in all directions, with 

 average northwesterly to north-northwesterly dips of about 70°. The original 

 dips due to tangential pressure have likewise been greatly modified by the 

 intrusion of the Rykert granite batholith. The failure to find recognizable 

 folds in the terrane has already been sufficiently noted. South of Summit creek, 

 zones A, B and C have been affected by a strong horizontal shift (a fault in 

 which there has been horizontal movement of one block past the other). At 

 the creek the three zones appear to be cut off entirely by a fault which is entered 

 on the map. A less important break cuts off zone B near the Boundary 

 line. With these exceptions the writer has failed to find structural elements 

 which can be definitely mapped. 



On Map No. 6 a long band of Kitchener quartzite is shown along 

 the western edge of the Kootenay river delta between the Rykert mountain 

 granite and the mouth of Summit Creek canyon. The, quartzite is referred 

 to the Kitchener formation on lithological grounds and there are many points 

 of resemblance to the Beehive quartzite. The microscope shows that inicroper- 

 thite is a relatively abundant constituent of all three quartzites while the felds- 

 pathic material of the quartzites belonging to the Priest River terrane is quite 

 different. In other respects also this quartzite along the river alluvium 

 corresponds well with the Kitchener formation in essential features. Though 

 the brushy slopes to the westward have not been thoroughly explored it appears 

 safe to postulate a great north-northwest fault on which these Kitchener beds 

 have been dropped down into contact -with the Priest River terrane. This 

 fault is shown on the map. Its exact course is represented only approximately; 

 further field-work is imperative before greater precision may be attained. The 

 fact remains, however, that this quartzite, which has thus been correlated with 

 the Kitchener and the equivalent Beehive quartzite, has been downthrown 

 through a vertical distance equal to the whole thickness of the Summit series 

 below the Beehive formation plus an unknown thickness of the Priest River 

 terrane. The downthrow may measure 20,000 to 30.000 feet. 



