120 THE ROYAL SOCIETY OF CANADA 



and the structural facts are inconsistent with its existence. Daly 

 has discussed the subject at length on different grounds, and has 

 reached the same conclusion. His account is here quoted in full. 

 After summarizing the hypothesis of Willis' paper as given above, he 

 says (12,f) : 



In passing, it may be noted that the evidence of the earlier Mesozoic peneplain 

 on which the Dakota and later Cretaceous beds were deposited, is not made clear. 

 It would seem probable that during the Mesozoic, this part of the Cordillera was 

 never far above sea-level. Most of the Mississippian limestone formation is still 

 preserved in the Crowsnest district only fifty miles to the northward on the strike 

 of the range. To the southeast its equivalent is likewise preserved beneath the 

 Cretaceous beds of the Belt mountains. We have seen that a great thickness of 

 the Mississippian limestone persists in the fault-blocks of the MacDonald range 

 just across the Flathead. Nowhere in the eastern part of the Cordillera north of 

 Colorado is there evidence of notable deformation of the Rocky Mountain Géosyn- 

 clinal between Mississippian and Laramie times. It seems likely, therefore, that 

 a great thickness of the Mississippian limestone was present in the MacDonald 

 range area before the Laramide or post-Laramide faulting dropped the large masses 

 of the limestone into lateral contact with the Altyn formation of the MacDonald 

 range; If this be granted, it follows that little erosion had been accomplished in 

 this latitude during the Mesozoic. The Mesozoic erosion-cycle could not have very 

 great significance in the region. 



Returning to the main theme, we may note that Willis's evidences for the 

 mid-Tertiary peneplanation are: (a) the truncation of the crumpled Cretaceous; 

 (b) the presence of accordant levels among the summits of the Galton-MacDonald 

 mountain group. Concerning the first point, it is not made certain that the trunca- 

 tion of the Cretaceous was observed outside the area which may reasonably be 

 supposed to have been overridden by the overthrust block of the Front ranges. 

 This thrust, as shown at Chief mountain very clearly, has not only crumpled the 

 Cretaceous beds but has sheared them off sharply at the plane of the Lewis thrust. 

 In some measure the observed truncation elsewhere may be attributed to this 

 constructional process, for there is clear evidence that the original eastern edge of 

 the overthrust block lay several miles to the eastward of the existing frontal escarp- 

 ments of the Lewis and Clarke ranges. Of course, erosion has modified the surface 

 of scission thus exposed by the retreat of the escarpments, but its base-levelling 

 effect must here have been vastly inferior to that which was demanded on the hard 

 quartzites and siliceous dolomites of the Lewis series. 



The argument from the accordance of summit levels cannot, in the writer's 

 opinion, be safely applied in any one of the four ranges now in discussion. In no 

 one of them is there any notable remnant plateau which can fairly be said to prove 

 general base-levelling in a former erosion cycle. The writer has already published 

 the grounds of his protest against using the accordance of peaks and ridges as an 

 evidence of two erosion c^'cles; a full abstract of that publication will be given at 

 the close of this chapter, to which the reader may turn. In brief, the point is 

 made that sub-equality of heights is to be expected from the early stage in the history 

 of every alpine mountain range. 



The evidences against the hypothesis of a mid-Tertiary peneplain on the Front 

 ranges seem to be powerful. First, the time allowed is not sufficient for peneplana- 

 tion or even past-mature development, followed by uplift and mature dissection in 



