REPORT OF TEE CHIEF ASTRONOMER 27 



SESSIONAL PAPER No. 25a 



the essential unity of the belt. The southern portion of the Okanagan valley 

 stretching from the mouth of the Similkameen river to the confluence with the 

 Columbia, has, however, a decided function in separating the Cascade range 

 from the very different mountains east of the Okanagan river. This portion 

 may be called the Lower Okanagan valley. 



SUBDIVISION OF THE ROCKY MOUNTAIN SYSTEM. 



The Eocky Mountain system, where it crosses the Forty-ninth Parallel, is 

 very definitely bounded: on the east, by the great plains; on the west, by the 

 Eocky Mountain Trench. (Plate 4.) This great element of the Cordillera is 

 itself so vast that, for the purpose of presenting the facts of its stratigraphy 

 and general geological history, the system must be subdivided into convenient 

 units. By a kind of international co-operation this is being accomplished. 



In Dawson r s reconnaissance map of the Eockies, published in 1886, he 

 designates as the ' Livingstone Eange ' the long Front range stretching from 

 the Highwood river at 50° 25' N. Lat. southerly to the North Kootenay Pass 

 at 49° 35' N. Lat. On the west it is bounded, for many miles, by the straight 

 valley of the Livingstone river and, in general, by the low mountainous area 

 covered by the Crowsnest Cretaceous trough. The name had appeared in 

 Arrowsmith's map of 1862, and in Palliser's of 1863, but Dawson gave the 

 range its first definition." Sixteen years later Willis made his admirable recon- 

 naissance of a part of northwestern Montana and proposed that the ' Living- 

 ston Eange ' be considered as extending across the International Boundary as 

 far as Lake McDonald.f There are, however, certain objections to making this 

 change of definition. These may be briefly stated. 



The crests of the Livingstone range, as delimited by Dawson, are composed 

 almost entirely of Devono-Carboniferous limestones. Midway in the range- 

 axis these rocks are interrupted, for a distance of about two miles, by a trans- 

 verse band of Cretaceous beds, but this local variation in geologic structure 

 involves no marked break in the line of crests. On the other hand, Dawson's 

 map and accompanying text indicate clearly that the range unit ends a few 

 miles north of the North Kootenay Pass. At that point a broad area of Cre- 

 taceous rocks squarely truncates the Devono-Carboniferous limestone and 

 forms comparatively low mountains of the foothills type. The independent 

 rangelet of which Turtle mountain is a part, is also composed of the Devono- 

 Carboniferous limestone and is in a similar manner cut off by the zone of 

 Cretaceous hills. The zone is fully twelve miles broad on the line of the axis 

 of the Livingstone range as mapped by Dawson. On the south of the zone, 

 lofty mountains of the Front range type are again to be found and these con- 

 tinue in strength to and beyond the International Boundary. The rocks com- 

 posing these mountains south of the broad, transverse Cretaceous belt are, 

 however, not of Devono-Carboniferous age but belong to a much older Cambrian 

 series underlain by conformable pre-Cambrian strata. 



* Annual Report, Geol. Survey of Canada, 1885, Part B, p. 80. 

 f Bull. Geol. Soc. America, Vol. 13, 1902, p. 312. 



