REPORT OF TEE CHIEF ASTRONOMER 619 



SESSIONAL PAPER No. 25a 



the range on the east and west sides. The higher summits in the Boundary 

 belt include Snowy mountain with an altitude of 8,507 feet and Cathedral 

 Peak with one of 8,610 feet. The range of the relief in a vertical sense is 

 therefore relatively great. 



The diversity of the relief is, however, all across the range, far less than 

 it is in the Selkirk range on the east or in the Hozomeen and Skagit ranges 

 on the west. Large areas of the Okanagan range are, in fact, plateau-like, 

 strongly rolling, with frequent dome-shaped mountains surmounting the general 

 surface by 1,000 feet or occasionally 2,000 feet. Snehumption creek has deeply 

 canyoned the great mass on the eastern side, evidently because its master 

 stream, the Similkameen, has been so successful in deepening its own gorge. 

 Yet only some eight miles up stream the Snehumption is flowing at an altitude 

 of 6,000 feet. Tor the next twenty miles farther west in the Boundary belt, 

 the lowest points in the main valleys, namely, the forks of the Ashnola river, 

 are respectively about 5,500, 4,900, 5,200, and 4,400 feet above sea. The next 

 ten miles of the belt, being drained directly into the main Pasayten river, 

 is naturally more deeply dissected. In all parts of the range the evidence is 

 clear either that this range has had a different geological history from the 

 greatly dissected Hozomeen range just across the Pasayten, or that the consti- 

 tuent rocks of the Okanagan range are much harder and have resisted erosion 

 much more effectively than have the rocks of .the western range. To the 

 observer in the field both views are manifestly correct. Almost throughout, 

 the Okanagan range is composed of exceedingly strong, granitic rocks; though 

 the batholith is composite, its different members have about the same power 

 of resistance to the weather. This composite batholith is, indeed, the largest 

 terrane of nearly homogeneous rock-strength in the entire trans-Cordilleran 

 section ; the few small, schistose roof -pendants represent the only ' soft ' rocks 

 in the range as sampled in the Boundary belt. On the other hand, the Hozo- 

 meen range is heterogeneous in composition; sediments, relatively weak as 

 compared with the granites, are there dominant and granitic rocks very sub- 

 ordinate. A priori it appears right to hold that this difference of hardness will 

 chiefly explain the different degrees of dissection in the two ranges, and that 

 there is no need to believe that the less dissected range has been lifted high 

 above baselevel at a time later than that during which the more dissected range 

 was raised. 



Granting that conclusion, the leading question arises as to the cause of the 

 plateau-like quality of the Okanagan range. Is its relatively flat upper surface 

 the result of peneplanation close to baselevel, so that the deep valleys of the 

 Similkameen and Pasayten rivers have been excavated as a result of an uplift 

 of this Cordilleran block for 7,000 or more feet ? Or can we explain the present 

 topography in terms of one erosion-cycle, the flatfish surface of the range 

 being a spontaneous and necessary result of erosion in that one cycle? This 

 second hypothesis may be coupled with the idea that minor changes of level 

 may have taken place during the one cycle; the essential and highly important 

 element wherein it differs from the first hypothesis consists in the fact that 



