104 THE ROYAL SOCIETY OF CANADA 



a later one in the mid-Tertiary (45,c). Daly takes the view that the 

 post-Cretaceous movements all belonged to a single orogenic episode 

 (12,g) before "the dawn of the Tertiary" (46,a). 



Evidence that has a direct bearing on the date of the Laramide 

 revolution is available from two widely separated localities. The 

 first locality is in the Cypress hills, which rise above the general sur- 

 face of the Great Plains in southwestern Saskatchewan. The other 

 locality is in the Flathead valley, well within the Rocky mountains 

 themselves. The evidence from the Cypress hills is the more conclu- 

 sive, though the Flathead evidence, which is not so convincing, never- 

 theless is corroborative of the other. Taken together, they afford 

 fairly satisfactory data as to the latest date at which the Laramide 

 revolution could have taken place. 



The Cypress hills are 200 miles from the present front ranges of 

 the Rocky mountains. They were studied by McConnell in 1883 

 and 1884. McConnell states (52,a) that the reason for the present 

 elevation of the Cypress hills is because of a sheet of resistant con- 

 glomerate which caps them, and has preserved them as an erosion 

 remnant surmounting the adjacent Great Plains to a height of 2,000 

 feet. Vertebrate fossils from this conglomerate were studied by Cope, 

 who gives their age as Oligocène (53). This Oligocène conglomerate 

 is usually composed of quartzite pebbles up to nine inches in diameter, 

 though the usual size is two to four inches. The quartzites are usually 

 white on a fresh fracture, but grey and flesh coloured tints are common 

 (52,b). These pebbles are derived from the quartzite formations of 

 the Rocky mountains (52, a) which, as already stated, are 200 miles 

 to the westward. 



The conglomerate^ rests unconformably on the subjacent 

 strata, the highest of which are stated by McConnell to be Laramie. 

 These Laramie strata are predominantly fine grained, contain coal, 

 and are evidently of freshwater origin (52,c). They are correlated 

 with strata of the Willow Creek and Porcupine Hills (Fort Union) 

 stages of Southwest Alberta (41,g). It is apparent that to carry 

 pebbles of the size and in the quantity described for a distance of 200 

 miles from their source a powerful current is required, which necessi- 

 tates, as McConnell points out, a gradient of at least 15 feet per mile 

 (52,a). 



The interpretation of the evidence afforded by this conglomerate 

 is that immediately preceding its deposition the mountain region 

 underwent a rapid and pronounced uplift. This uplift is considered 



^McConnell described it as Miocene but the later determination of the fossils 

 by Cope gives the age as Oligocène. 



