SURFACE MATERIALS. 41 



Before continuing the notes made in the deeper river sections to the 

 westward of Lethbridge, a few words may be devoted to the character of 

 the general surface of the plain corresponding to the sections above cited. 

 This is well shown in numerous fresh cuttings along the line of railway 

 between Dunmore (near Medicine Hat) and Lethbridge, a distance from 

 east to west of 100 miles. Whether in the rolling prairie toward the east 

 or the nearly level prairie to the west, the surface is almost uniformly 

 composed of gray or brownish gray silty or loamy material, of which 

 the depth may be stated to vary from two to five feet, although cer- 

 tainly greater in some places. On the crests of knolls and ridges and 

 in some of the valleys which have evidently been cut out by postglacial 

 flows of water, this deposit has been removed, leaving a grayish boulder- 

 clay, which sometimes contains large stones at the surface. The stones 

 are generally Laurentian, but are seldom abundant. It might be sup- 

 posed that the prolonged action of rains or that even of the winds would 

 in time produce a surface deposit of this kind, but much of the plain is 

 so entirely flat that such explanations appear improbable. Neither are 

 the projecting ridges notably bouldery, as should be the case if much 

 denudation of their finer material had occurred, and the circumstances 

 favor a belief that the silty deposits have been laid down in a body of 

 rather shallow water, coextensive with the j^lain itself, in which some 

 slight rearrangement of the exposed parts of the boalder-clay has taken 

 place. There is some appearance of rolled gravelly deposits about the 

 slopes of the ridges, but the cuttings are insufficient to show these fully. 



Following the axis of the main depression already alluded to, no ex- 

 posures have been found further to the westward in which the lower and 

 an upper boulder-clay are clearly distinguished, and as the sections are 

 not continuous, it becomes impossible to decide in each case which is 

 represented. In an exposure nearly opposite Rye Grass fiat, 12 miles 

 Avest of Lethbridge (52 miles from the base of the mountains), locally 

 upturned Laramie beds are overlain by 10 feet of stratified sand and silt, 

 followed by 20 feet of boulder-clay, which again is followed by 12 feet of 

 rolled gravels, apparently replaced in a short distance horizontally by 

 stratified sands. The whole section is capped by some feet of the loamy 

 superficial silts above described. The boulder-clay seen in this section 

 includes a number of discontinuous layers of sand and gravel. 



Another section of considerable length two miles and a half below 

 Macleod (45 miles from the base of the mountains, elevation 3,024 feet) 

 was carefully examined by Mr McConnell, and is described by him as 

 follows : 



" The boulder-clay is here 45 feet in thickness from the river level and 

 is overlain by 20 feet of sands and silts which contain layers of finely 



