TILL OF THE SASKATCHEWAN PLAINS. 397 



forty miles of them, as far as Calgary, on the Canadian Pacific railway, and 

 from there southward to the international boundary it keeps at about the 

 same distance from the mountains. North of Calgary the western edge of 

 the great sheet of till crosses the Red Deer and North-Saskatchewan rivers 

 at approximate elevations of 3,000 feet above the sea, the latter in long. 

 11")° W. Further north it is stated by Dr. Dawson to cross the Peace river 

 in lat. 56° N., long. 119° W. To the south its boundary everywhere lies 

 on the United States side of the Forty-ninth parallel of latitude. North 

 of or near this geodetic line it covers all the country of the plains without 

 regard to elevation, with four exceptions, viz., the upper portions of the 

 Sweet Grass hills above 4,660 feet, the Cypress hills above 4,400 feet, the 

 Hand hills above 3,400 feet, and Rocky Spring plateau above 4,100 feet. 

 The general character of this great sheet of drift is remarkably uniform 

 throughout, being essentially composed of a gray, more or less sandy clay, 

 massive in character, and holding numerous pebbles and bowlders. It is 

 largely composed of the debris of the Cretaceous and Tertiary rocks that 

 surround or immediately underlie it, consisting probably of the parts of 

 these strata that were rotten from long exposure to the weather during the 

 ages that intervened between the close of the Laramie period and the com- 

 mencement of that of glaciation. By this latter agency the rotten rock was 

 kneaded up, with the bowlders and pebbles transported from a distance, into 

 a homogeneous mass. That the till is local is clearly seen where the under- 

 lying rock has any very marked characteristic by which it can be recog- 

 nized — as, for instance, the rocks of the Edmonton series of the Laramie, 

 which are associated with numerous beds of lignite. Overlying these rocks, 

 and especially for some distance south of a lignite outcrop, the drift is filled 

 with pieces of lignite sometimes as large as a hen's egg, and the whole mass 

 becomes dark in color from its presence in minute fragments. Another in- 

 stance is recorded by Dr. Dawson where the drift has a distinctly reddish 

 tint, derived from some neighboring reddish clays of the Laramie formation. 

 The bowlders are, however, largely of eastern origin, being composed of 

 granitoid gneiss, mica-schist, quartzite, diabase-trap, gneiss-conglomerate, 

 and stratified Paleozoic limestone, those of limestone, as well as an occa- 

 sional one of the other rocks, being usually irregular in shape, with smooth, 

 polished surfaces and sharply marked glacial strhe. The pebbles included 

 in the till throughout the western portion of the district, where they consist 

 largely of white quartzite, the same as that composing the Miocene gravels 

 on the Cypress and Hand hills, are doubtless partly of local origin, having 

 been derived from the gravel on these hills, or from other areas that have 

 been entirely denuded away. Some are also probably derived from the 

 parent beds of Cambrian quartzites in the Rocky Mountains. A few of 

 gneiss are almost everywhere met with, and while the western quartzites 



