REPORT OF TEE CHIEF ASTRONOMER 615 



SESSIONAL PAPER No. 25a 



an unusually thorough treatment of the physiography in this part of the 

 trans-Cordilleran belt. In his 1902 report Brock has given a short account of 

 the district, but the physiographic study involves additional field-work before 

 much can be written.* 



Midway Volcanic District. — Excepting possibly the Anarchist plateau, the 

 relief in the region about Midway is the least in the whole Boundary belt. The 

 Kettle river at the town is about 1,900 feet above the sea and the mountains are 

 seldom over 4,000 feet high. We are, in fact, approaching the Belt of Interior 

 Plateaus. Between that belt and the more sharply accidented topography farther 

 east, the Midway district is a transitional province. 



The local topography shows considerable variation in character as it is 

 followed through the areas of Paleozoic rocks, Tertiary volcanics, and Kettle 

 River sediments. The first and third terranes are areally of little importance; 

 the topography is that induced by erosion on a deformed mass of lava flows 

 and pyroclastics of highly variable resistance to the weather. Glacial erosion is 

 very subordinate in its effect of modifying the forms of the mountains, while 

 Glacial drift veneers the slopes with depths which, for so large an area, are 

 unmatched in the whole trans-Cordilleran section. The Boundary belt, from 

 Record mountain ridge near Rossland to the higher summits of the Okanagan 

 range was completely covered by the ice-cap of the Glacial period at the time 

 of the maximum extension of the cap. The Forty-ninth Parallel is near the 

 front of the slow, south-moving ice of that time; the reason is clear why the 

 drift cover is thick and also why both ice and drift have occasioned many 

 changes in the courses of the pre-Glacial lines of river flow. Some of these 

 changes have been referred to in the preceding chapter. An important result 

 of glaciation has thus been to obscure the physiographic history of the region 

 even more than it would have been if it carried simply the record of events 

 from the time of the Jurassic orogenic revolution to the dawn of the Glacial 

 period. 



Since the older rocks of the region have undergone severe deformation in 

 the late Jurassic (if not at the close of the Pennsylvanian period), and in the 

 period of the Laramide revolution, and since these and the Oligocene sediments 

 and lavas of the Kettle River formation have suffered distinct deformation in a 

 post-Oligocene period, it is almost or quite impossible to relate the drainage 

 courses to constructional slopes. In this report no attempt is made to discuss 

 the rivers and creeks from the genetic point of view. The same remark must 

 be made concerning the streams now draining the plateaus on the west, where 

 the problem is essentially as difficult. 



The physiographer's attention will in this district, as in the plateaus, be 

 attracted to details of land-forms and of erosional processes which, on account 

 of the unforested character of much of the region, are conspicuously illustrated. 

 A few of these cases may be mentioned. 



The gravel and sand terraces of the Kettle river are in organic connection 

 with those of the Columbia into which the former river flows. As the master 



* See R. W. Brock, Ann. Eep. Geol. Survey of Canada, Vol. 15, 1902. p. 93A. 



