602 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



Much of the interest of the scenery is due to the architectural 

 effects, which in turn are controlled by the bedded structure of both ranges. 

 The constituent rocks belong to the most heterogeneous part of the Rocky 

 Mountain Geosynclinal ; strong and weak beds alternate very often through the 

 series and advanced erosion has brought out the familiar repetition of scarp 

 and talus. The dips of the strata are generally low, so that the appearance of 

 coursed masonry in infinitely varied design characterizes these ranges. Most 

 of the summits are well above tree-line (7,200 to 7,500 feet), whereby the profiles 

 of the many retreating escarpments are kept sharper than they would be under 

 such a heavy forest-cap as that mantling the more westerly ranges. A yet more 

 powerful influence in fashioning the truly magnificent peaks, precipices and 

 savage, serrate ridges is the local glaciation which, as noted in the foregoing 

 chapter, has been so important in the Front ranges. The development of the hun- 

 dreds of beautiful cirques has, however, been greatly aided by the heterogeneity 

 and the structure of the sedimentary rocks in which cirque and basin have been 

 excavated. It appears probable that the head-wall recession, with consequent 

 formation of the steepest cliffs in the region, has been specially hastened 

 through the natural blocking of the strata by joints and bedding-planes; such 

 structures must have aided the frost in quarrying along the schrund-lines of 

 the many local glaciers. The sharpening of the profiles through the work of 

 the Pleistocene cirque-glaciers is well illustrated in such views as that in Plate 

 9. Similar contrasts between the pre-Glacial topography and that directly 

 caused by head-wall recession are shown in the Wasatch, Uinta, and Big Horn 

 ranges of the United States.* 



Notwithstanding the intensity of Glacial erosion in the Clarke-Lewis 

 mountain group, the major topographic features are, as usual in large ranges, of 

 pre-Glacial origin and have been caused by crustal movement and normal 

 stream erosion. The relatively simple structure of the mountain group — 

 synclinal with minor arches and faults developed in both ranges — suggests a 

 comparatively simple origin for some of the streams and valleys. The Mineral 

 Creek- Waterton River valley has already been described as apparently conse- 

 quent in origin, the stream flowing along the axis of the syncline. Akamina 

 creek, which is followed by the South Kootenay Pass trail, is located in the 

 bottom of a minor synclinal roll in the midst of the master syncline, and may 

 also be of direct consequent origin. Kishenehn and Starvation creeks are 

 examples of just such stream courses as we should expect to have been formed 

 on the eastern slope of the Flathead fault-trough, in consequence of that graben- 

 sinking. Many other roughly parallel creeks and canyons on this slope of the 

 Clarke range may likewise be classified as probably consequent in origin. 

 Kintla creek is located on a distinct fault which may have been the line of 

 an actual depression in the original deformation of the Lewis series of sedi- 

 ments; if so, this creek and its canyon are consequent. Yet we can hardly 

 exclude the possibility that the fault-zone has functioned as a natural weak 



* See the recent monograph by W. W. Attwood on the Uinta and Wasatch 

 Mountains, Prof. Paper No. €1, U.S. Geol. Survey, 1909; especially Plates 4 and 8. 



