82 THE ROYAL SOCIETY OF CANADA 



occurs in southern Alberta at the 49th parallel and is situated along a 

 line of faulting. Mackenzie's conclusions on the origin of the valley 

 are as follows: 



"The structure of the Flathead map-area may be succinctly 

 described as that of a downfolded, warped, monoclinal fault block, 

 with northeast strikes, and for the most part, southeast dips; bounded 

 on the northeast and southwest by normal faults with a northwest 

 strike, the upthrown sides being on the northeast, and southwest, 

 respectively. 



"The upthrown blocks form the limestone mountains in the 

 southwestern part, and these just north of the map-area, and with 

 their southwestward dipping strata partake of the structure of the 

 Macdonald range to the west. Between these older rocks is a down- 

 thrown block of younger beds, which in the western portion of the 

 district, lie with moderate dips diverging from a low north-south 

 anticlinal axis, less pronounced toward the south, which is located a 

 mile or so east of the western edge of the map-area. 



"To the east of this axis for a short distance the strata lie in low, 

 undulating, minor folds, then dip more sharply to the eastward, giving 

 this fault block its essentially monoclinal character. 



"Apart from the major breaks mentioned, faulting is not pro- 

 nounced, and no other breaks have been certainly observed. It is 

 probable, however, that strike faults of relatively small displacement 

 will be found during the development of the coal seams, and may 

 prove a factor of some consequence in mining operations. 



"The structure of the Tertiary Kishinena formation is only 

 imperfectly known. Dips up to 50° have been observed, also local 

 unconformities, so that it is plain that those beds have been strongly 

 deformed, and probably more than once. As all the dips are toward 

 the east or southeast, a tilting in that direction is apparent. The 

 inference seems clear that the beds were formed in part before the 

 slipping along the great fault on the east of the Flathead valley was 

 completed, and that slipping occurred during their period of accumu- 

 lation. This interpretation places the date of the beginning of normal 

 faulting as early Eocene, which is earlier than the Miocene date as- 

 signed to it by Willis.^ The major part of the normal faulting may be 

 assigned to a period immediately succeeding the Laramie revolution, 

 as it occurred as soon as the compression of that organic disturbance 

 ceased. Later, lesser slipping continued into the Eocene, and perhaps 

 for a longer time." 



1 Bull. Geol. Soc, Am., vol. 13, 1902, p. 34-t. 



