90 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



observed down-flexure of the Appekunny at Starvation creek is but an inci- 

 dental result of a great normal fault or system of normal faults which limits 

 the Flathead valley on the east. In this view the writer's observations agree 

 with those of Willis, who states that the structural relations at the western 

 side of the main syncline ' are those of a normal fault of great displacement, 

 and downthrow on the west. From the topographic relations the position of 

 this normal fault is inferred to be along the base of the Livingston [Clarke] 

 range, the downthrown block underlying Flathead valley.'* 



The axis of the Akamina creek valley is located on a flat syncline, with 

 an axial trend parallel to those of the main syncline and the Cameron Falls 

 anticline, namely, northwest-southeast. 



Normal faults are rare and none, except the North Fork fault, shows strong 

 displacement. The attitudes of the beds to north and south of the Kintla 

 lakes suggest a fault following the axis of the valley, with downthrow on the 

 north. The movement was slight but apparently sufficed to locate the erosion 

 channel of which the present valley is the greatly enlarged descendant. A 

 second, neighbouring fault has brought the red Grinnell beds down into con- 

 tact with the lower beds of the Appekunny, indicating a moderate throw on the 

 east of the fault. 



GREAT LEWIS OVEBTHRUST. 



The most important structural feature of the range is a great 

 thrust by which the eastern part of the main syncline, together with 

 the Mt. Wilson (Lewis range) block, has been driven eastward or north- 

 eastward over the Cretaceous formations of the plains. The nature and relations 

 of this thrust are quite similar to those described by McConnell at the Bow 

 River pass and Devils lake, 150 statute miles to the north-northwest, and to 

 those worked out by Willis at Chief mountain and elsewhere in Montana.f The 

 proof that the thrust-plane extends to Waterton lake suggests the possibility 

 that the one great dislocation extends from 48° 30' N. Lat. to at least 51° 30 7 

 N. Lat. (See Figure 6.) 



The demonstration that the thrust-plane passes under the Clarke range 

 is not as full as that adduced by Willis for the Lewis range. In the more 

 westerly range the natural rock exposures in the Boundary belt are not of 

 themselves sufficient to show the fact. The reason for believing that at least 

 the eastern part of the Clarke range block has actually overriden the plains 

 strata is found in the log of the deep boring made by the Western Oil and 

 Coal Company at Cameron Falls, on the west side of Waterton lake. At that 

 point the drill penetrated 1,500 feet of silicious dolomites which, as above noted 

 (page 55), form the downward extension of the Lewis series. At that depth 

 the drill suddenly entered soft shale which continued for another 400 feet, 



* B. Willis, Bull. Geol. Soc. America, vol. 13, 1902, tp. 344. 



fE. G. McConnell, Ann. Eep. Geol. Survey of Canada for 1886, Part D, p. 31; B, 

 Willis, Bull. Geol. Soc. America, Vol. 13, 1902, p. 331 ; D. B. Dowling, Bull. Geol. Soc. 

 America, Vol. 17. 1906. p. 296. 



