76 THE ROYAL SOCIETY OF CANADA 



The great fault on the eastern side of the trench is a hinge fault 

 since the Devono-Carboniferous limestone exposed at Elko on the 

 wall of the trench gradually descends in going northward until at the 

 Bull River it unites with the Carboniferous limestone which floors 

 the trench. At Bull River the Carboniferous limestone occupies the 

 floor of the trench while the eastern wall of the trench is composed 

 of rocks which may be correlated with the Aldridge and Creston 

 formations of the Purcell series. Hence the throw at this point is very 

 large. The fault on the west side of the trench is a continuation of the 

 fault farther south and which was described in a previous paragraph. 

 Therefore, the structure of the trench at Bull River is a continuation 

 of that farther south at the boundary line. 



That part of the trench which lies between Bull River and Canal 

 Flats has not been studied in detail but the two flanks of the trench 

 are composed of rocks of the Purcell series. The floor as far as our 

 knowledge goes is not covered with Carboniferous limestone. That a 

 fault exists in this portion of the trench is almost certain since the 

 rocks of the two flanks belong to different members of the Purcell 

 series in addition to the fact that the strikes of the formations on the 

 two flanks are different. 



3. At Canal Flats {Upper Columbia Lake.) — The stratigraphie 

 succession on the two flanks of the trench at Canal Flats is expressed 

 in the following table: 



Western Flank Eastern Flank 



Devonian Jefferson limestone 



Disconformity 

 Upper Cambrian Sabine formation 



Beltian — Kitchener formation .Middle Cambrian Elko formation 



The rocks of the western flanks belong to the Purcell series and 

 are provisionally correlated with the Kitchener formation. The 

 trench in this vicinity is about 2 miles wide. The eastern wall rises 

 abruptly out of a flat, drift-covered floor. At the base of the wall, the 

 Elko formation outcrops and is overlain conformably by the fossil- 

 iferous Middle Cambrian (Sabine) formation which is in turn overlain 

 by the Devonian limestone. The eastern flank does not rise abruptly 

 from the drift-covered floor but gradually ascends, the lower slopes 

 being marked by small hills. 



The structure, as shown in Figure 1, is a normal fault with the 

 apparent downthrow on the western side, bringing the Beltian- 

 Kitchener formation in contact with the Middle Cambrian Elko 

 formation. The throw is purely a matter of conjecture and may be in 

 the neighbourhood of 10,000 feet. 



