44 G. M. DAWSON — GLACIAL DEPOSITS OF SOUTHWESTERN ALBERTA. 



characterized by moraines, evidently due to local glaciers from the Rocky 

 mountains, and the indurated boulder-clay of the Mill Creek section is 

 believed, like the moraines, to be a deposit of these glaciers. The lower 

 gravels in this case and in that of Pincher creek are obviously due to pre- 

 glacial streams flowing from the mountains, and, although the name Sas- 

 katchewan gravels may be applied to them, they here evidently antedate 

 the eastern gravelly representative of the Rocky mountains or earliest 

 boulder-clay. Further to the east, where this boulder-clay gradually 

 passes into such gravels, there is no means of distinguishing between 

 Avholly preglacial beds and those which may have been formed during 

 the main period of the Rocky Mountain glaciers. Many exposures of the 

 Saskatchewan gravels may include both, and this without necessitating 

 the supposition of any great chronologic break. 



Southern Part of thk Porcupine Hills. 



Having thus followed the main southern line of approach at low levels 

 to the mountains, attention may next be given to tlie southern end of the 

 Porcupine liills, whicli overlooks this avenue on the north side, at a dis- 

 tance from about 15 to 30 miles from the base of the mountains. Oleson 

 and Beaver creeks flow southward from this end of the hills, and it was 

 chiefly in the vicinity of these streams that the observations noted were 

 made. 



In traveling westward from Macleod (situated on the plains at an ele- 

 vation of 3,070 feet) to Oleson creek by the regular trail north of Oldman 

 river, a distance of 14 miles, a gradual ascent is made which becomes 

 greater as the flanks of the hills are reached. The following terrace- 

 levels were noted on this route : 



North of Macleod an extensive gravel i)lain forming the angle between 

 Oldman and Willow rivers is reached. This rises gradually from 3,130 

 feet in a distance of a couple of miles to 3.220 feet. Its surface is not abso- 

 lutel}^ flat, but is diversified l)_y low swells or ridges, which generally trend 

 north and south. 



This ])lain is bounded to the west by a distinct rise leading to another 

 similar plain or wide terrace, also gravell}^ of which the eastern part is at a 

 height of 3,275 feet, and which continues to slope up gradually to the west- 

 ward. The gravels of this plain and the last are composed chiefly, but 

 not entirely, of well rolled Rocky Mountain quartzites. At 3,286 feet on 

 this second [)lain is found running northward a line of remarkable large 

 boulders,* composed of quartzite or conglomerate. These are identical 



* These remarkable Vjoulders are in size and composition unlike any observed in the boulder- 

 clays. They have undoubtedly been water-borne and may probably have been derived from some 

 particular region of the Laurentian plateau which became tributary at a later stage of the Glacial 

 period. 



