PHYSICAL AND CLIMATAL CONDITIONS. 1 2~t 



The liistoiy of the coteau would seem to have been as 

 follows : 



1. The excavation in pre-glacial times of an edge or 

 esearimieut in the gently sloping surface of the Cretaceous 

 and Laramie beds, and the cutting by subaerial causes of 

 couk'es and valleys of streams in this escarpment. 



2. Submergence in the glacial period, in such a manner 

 as to permit heavy ice loaded with Laurentian dchrU to 

 ground on the edge of the escarpnient and deposit its 

 burden there, while at the period of greatest submergence 

 deep water must haAc extended nnich further westward. 

 Tiiese conditions must have continued for a long time and 

 with somewhat variable deptli of water. 



'?. lie-ele\ation, during whicii gravel ridges wen; 

 formed, until at length the coteau became the coast-line 

 of a shallow sea, which lingered at a later date along the 

 line already referi'ed to in advance of the coteau. 



4. On the re-elevation of the country, the transverse 

 ravines and vallevs were so eft'ectuallv dammed up l)v 

 the glacial ridge, that the surface waters of tiie regitjn, 

 now comparatively arid, have to remain as alkaline lakes 

 and poiuls behind the coteau. 



The upper })i'airie plateau, extending from the coteau 

 to the Itocky mountains, has, on its general surface, com- 

 paratively few l)oulders ; yet these are locally numerous, 

 especially on the eastern and northern sides of some 

 gentle elevations of the prairie. They cfisist, as before, 

 of Laurentian gneiss, Huronian schists, antl yellow Silurian 

 limestone, all derived from the eastern side of the plains, 

 some of the boulders of Laurentian gneiss being of great 

 dimensions. Some of these have been used in modern times 

 by the buffalo as rubbing-stones,and are surrounded by basin- 

 shaped depressions formed by the feet of these animals. 



