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



horizon eastern gneissic and limestone boulders and pebbles, the latter 

 often striated, are common, but no rocks of undoubted western origin 

 were observed. The beds of well rounded quartzite pebbles below the 

 boulder-clay, on the other hand, are derived, so far as known, entirely 

 from the west, although they may here in part represent redistributed 

 Miocene conglomerates like those of the Cypress hills, which were brought 

 down from the mountains in Miocene times. 



" Twent}^ miles above the Blackfoot crossing or 175 miles above Medi- 

 cine Hat, where the next section was examined, the conditions have 

 entirely changed. At this particular place the underlying gravels are 

 absent and the boulder-clay holds both eastern and western drift inti- 

 mately commingled throughout, pebbles of unmistakable Laurentian 

 gneisses and well characterized Rocky Mountain limestones often l3^ing 

 side by side in the same hand specimen. The relative proportions of the 

 two drifts at this point, 100 miles east of the mountains, measuring along 

 tlie valley of the Bow, are nearly equal. In descending the river western 

 drift of a recognizable character gives out in the boulder-clay before Medi- 

 cine Hat is reached, and in ascending it the eastern drift gradually dimin- 

 ishes in relative quantity and disappears altogether above Calgary, 40 

 miles east of the mountains, or about 50 miles if the Bow valley be fol- 

 lowed. 



" Twenty-five miles above the Blackfoot crossing a boulder-clay section 

 110 feet in thickness is exposed. The boulder-clay is here separated into 

 an upper and lower division by a band of stratified sands, the lower 

 boulder-clay being darker colored than the upper one and differing from 

 it also in containing a larger proportion of western drift. The junction 

 between the two boulder-clays is not straight, but follows an irregular 

 wavy line. 



"At Pine canyon, eight miles above the last section, the Laramie sand- 

 stones are overlain by the Saskatchewan gravels 10 feet thick, above 

 which is a peculiar morainic-looking deposit 40 feet thick, consisting of 

 angular blocks of Laramie sandstone of local origin, gneisses and lime- 

 stones from the east and limestones and quartzites from the west, all 

 mixed confusedly together in a matrix of coarse sand and clay. 



" Four miles above the last exposure the boulder-clay, here 50 feet 

 thick, rests directly on the older rocks. The ratio of eastern to western 

 drift in this exposure was estimated at about 1 or 2. A notable feature 

 of the section is the presence in it of a gneissic boulder of eastern origin 

 measuring fully three feet in diameter. The ordinary size of the eastern 

 pebbles in the boulder-clay along this portion of the river seldom exceeds 

 three inches in diameter. 



" Two miles above the mouth of Highwood river the Saskatchewan 



