DEDUCTIONS FROM RELATIONS OF THE DRIFT 551 



ined, of water-worn pebbles from formations exposed in the mountains 

 60 miles to the west and southwest, mostly of pink and white quartzites, 

 with smaller percentages of maroon and greenish argillite, diorite, amyg- 

 daloidal trap rock, gray limestone, and conglomerate containing black 

 chert pebbles. At one point two or three granites were found among the 

 loose pebbles in the excavation, but it was thought they might have rolled 

 down from the drift higher in the slope which was deposited by the Kee- 

 watin Glacier. None such were found embedded in the stratified gravel. 

 The top of the gravel is marked by a sharp horizontal line, and at only 

 one point was any evidence of disturbance of the bedding, such as might 

 be expected to result from their being overridden by the continental ice- 

 sheet. Perhaps the gravel was cemented by ice to a solid conglomerate 

 when such overriding took place. 



By far the larger percentage of the pebbles in the dense compact lower 

 till (B) is from the Eocky Mountains, probably derived by the glacier 

 from deposits of gravel in the valleys such, as those composing the under- 

 lying bed. Intermingled with these are granites and other crystalline 

 rocks from the Laurentian formations west of Hudson Bay, showing that 

 the till was deposited by the Keewatin ice-sheet. The surface of the 

 lower till is uneven, especially in the second exposure described, and the 

 oxidation of the upper part of this till is evidence of its exposure to 

 weathering prior to the deposition of the upper till. 



The stratified beds (C) indicate deposition during a stage of deglacia- 

 tion. At the exposure north of the bridge there is nearly 50 feet of inter- 

 bedded fine sand and loess-like silt resembling an eolian deposit. Over- 

 lying this is 1 to 3 feet of fine, laminated, papery silt. The relations 

 indicate that this deposition was followed by a period of erosion, for the 

 deposit thins abruptly toward the east side of the exposure until it 

 pinches out entirely between the lower till (B) and the upper till (D). 

 The upper till (D) mantles the slope and extends thence up to the up- 

 land as though it lay on the side of an interglacial valley. The extent of 

 the interglacial deposit (C) northward down the valley was not deter- 

 mined. There seems to be considerable of the loess-like material on the 

 east side north of the railway bridge, where such materia] exposed in the 

 sides of a ravine is being used in making brick. South of the railway 

 the bed (C) consists of partially cemented, laminated, grayish, tine sand 

 or silt. A small opening in the grassy slope at one point in the side of a 

 ravine back of the power-house exposed as part of these deposits the 

 following : 



