REPORT OF THE CHIEF ASTRONOMER 91 



SESSIONAL PAPER No. 25a 



when the work was stopped, and the bore-hole, for the time at least, abandoned. 

 These shales have been examined by Mr. T. Denis, of the Canadian Department 

 of Mines, and by the writer; the material proved to have the habit of typical 

 Cretaceous, probably Benton, sediments. Their colour, softness, and carbona- 

 ceous character are quite different from those characterizing any phase of the 

 Lewis series; on the other hand the shales are sensibly identical with fossili- 

 ferous Cretaceous beds occurring below the thrust-plane at Chief mountain. 



How much farther west the thrust has caused the superposition of the 

 Belt terrane on the Cretaceous can only be conjectured. It is not impossible 

 that the entire Clarke range in this region represents a gigantic block loosed 

 from its ancient foundations, like the Mt. Wilson or Chief mountain massifs, 

 and bodily forced over the Cretaceous or Carboniferous formations. In that 

 case the thrust woxild have driven the block at least forty miles across country. 

 Such a speculation is of some interest in giving one explanation of the emana- 

 tion of gas and petroleum in the Flathead valley and in the heart of the Belt- 

 Cambrian rocks at lower Kintla lake. (Plate 13.) These hydrocarbons would 

 thus be considered as originating in the Carboniferous limestone or in the 

 Cretaceous sediments underlying the thrust-plane. Since the Carboniferous 

 limestone is highly bituminous, that formation would naturally offer an original 

 source for the oil and gas. 



On the other hand, a second hypothesis may be framed, whereby the seep- 

 ages in the Flathead valley are thought to originate in the Carboniferous 

 limestone which was faulted down during the formation of the Tertiary fault- 

 trough, while the seepages at Kintla lake are interpreted as emanations from 

 Carboniferous limestone locally underthrust on the west side of the main 

 syncline of the Clarke range. On this view the Waterton lake thrust need not 

 extend much farther west than the lake itself. 



Or, thirdly, one might conceive that the hydrocarbons originated directly 

 in the Beltian rocks themselves (see page 53), so that the existence of the seepages 

 would have no direct bearing on, or afford no proof of, any large-scale thrust- 

 plane beneath the western slope of the range. There is as yet no decisive 

 evidence forcing a choice among these three hypotheses. The known extent of 

 the bodily movement represented in the Waterton lake thrust is, at a minimum, 

 about eight miles, as measured on the perpendicular to the line tangent to 

 Chief mountain and the outpost mountains of the Clarke range. The move- 

 ment has probably been ten miles or more and may be as much as forty miles. 



The thrust proved at Waterton lake is doubtless a northern continuation 

 of the ' Lewis thrust ' described by Willis as explaining the peculiar relations 

 of pre-Cambrian and Cretaceous at Chief mountain and southward. Willis 

 has, in fact, stated that he has traced the outcrop of the thrust surface around 

 Mt. Wilson to Waterton lake. He concludes that ' according to these observa- 

 tions, the relation of the Lewis and Livingston [Clarke] ranges, en echelon at 

 the 49th parallel, is an effect of step-like though very gentle flexure in the 



