616 DEPARTMENT OF TEE INTERIOR 



2 GEORGE V., A. 1912 



stream has sunk its channel into its own. drift-filled valley-floor, the branch 

 stream has been compelled to cut into the thick mass of washed detritus 

 deposited in the Kettle valley in the late Glacial time. In the same way the 

 affluents of the Kettle river, like Saw (or Baker)- creek, have entrenched them- 

 selves in the local drift deposits. As is to be expected, the terraces so developed 

 are proportioned in height to the size of the corresponding streams, so that 

 the Kettle river benches are low when compared with those of the Columbia but 

 are much more strongly developed than those of its own branches. 



The formation of the Kettle river terraces has clearly followed the process 

 generalized by Davis from the field relations of the similar terraces along the 

 New England streams* This process may be quickly understood from a study 

 of Davis's papers on the subject. In this place let it suffice to say that the 

 preservation of the terrace sands has been accomplished by the presence of 

 ' defending ' rock-spurs which the degrading, though meandering stream 

 encounters at intervals, as it penetrates the loose material of the late-Glacial 

 alluviation. The spurs inhibit the meandering of the stream; the width of 

 the meander belt is thereby limited and the high-lying sands and gravels are 

 safe from the river's attack until the much tougher rock-spurs have been des- 

 troyed as the result of much more prolonged lateral corrasion than post-Glacial 

 time has yet allowed. 



Several cases of truncated and compounded alluvial cones were observed in 

 the Boundary belt. One of these is illustrated in Plate 65. 



In this region for the first time we find two tree-lines, as Russell and other 

 geologists have recorded in the dry country south of the Boundary. The upper 

 line is determined chiefly by cold and drought. The lower line is determined by 

 drought primarily. The forest is here, therefore, distributed only on intermediate 

 slopes in the case of the highest mountains, like Mt. McKinney. Because of 

 the low altitudes of most of the mountains, however, the lower tree-line only 

 is generally visible in the Midway district. The height of this line is much 

 more variable than even the normal upper tree-line. The exposure of the slope, 

 the texture of the soil and rock beneath and yet other conditions must obviously 

 affect the position of this tree-line at any locality. 



Interior Plateaus. — The Anarchist old-mountain plateau merits its 

 name although its general surface shows differences of elevation of as much as 

 1,300 feet. As a distinct unit with a culminating point of nearly 5,000 feet, it 

 stands above the Okanagan valley which is about 930 feet above sea at the 

 edge of Osoyoos lake. Practically the whole of the plateau is composed of greatly 

 crumpled Paleozoic sediments and interbedded greenstones, except where these 

 rocks are replaced by a part of the Osoyoos batholith. 



Across the lake, and somewhat lower in altitude, is the Kruger-mountain 

 plateau, composed of the same Paleozoic rocks together with various bodies of 

 plutonic intrusives supposed to date all the way from the late Jurassic to the 

 Miocene. The deep valley of the Similkameen separates the plateau from the 

 Okanagan range. , 



So far as the field evidence goes, there is no reason to think that either of 

 these massifs has been covered by sediments other than land-wash and Glacial 



* W. M. Davis, American Journal of Science, Vol. 14, 1902, p. 77. 



