49 



the hard gneisses of the Laurentides on the north and the 

 resistant sandstone belts of the Appalachian ridges on 

 the south. Uplifted, like the other lowlands, in mid- 

 Tertiary time, it has been widely dissected by the river 

 and its tributaries, and subsequently drowned. The 

 tide now runs up the St. Lawrence to Lake St. Peter, 

 80 miles (128 km.) above Quebec. For at least a part 

 of the Pleistocene period the valley stood even more 

 deeply beneath the sea. 



According to Chalmers, the glacial history of this region 

 is very complex; for there seem to have been three systems 

 of land ice in the field: first an ice sheet appears to have 

 spread from the Appalachian highlands of southern 

 Quebec and New Hampshire northward as far as the St. 

 Lawrence; next came an invasion of ice from the centre 

 east of Hudson bay which crossed the St. Lawrence as 

 far east as Quebec but not farther; and finally there is 

 thought to have been a southwesward movement of ice 

 from the Laurentian mountains. Local glaciers seem 

 to have descended from these mountains in the closing 

 stages and floating ice drifted up the estuary, which at 

 that time was much deeper and wider. Marks of this 

 drifting ice are found, at various points on the south 

 shore. The evidences of these several stages or epochs 

 of glaciation cannot be regarded as yet sufficiently in 

 hand to justify conclusions regarding them. 



At the close of the last Glacial epoch the region around 

 Quebec stood approximately 600 feet (180 m.) lower 

 than now. By a differential upwarping, the old seafloor 

 sediments and associated shorelines have been lifted to 

 their present height above the sea. The obscure character 

 of these raised beaches suggests that the land was already 

 emerging from the sea when the ice sheet melted away, 

 and that it continued to rise rather steadily and rapidly 

 until approximately the present altitude was established. 

 Gravelly beaches on the hills behind Chateau Richer, 

 15 miles (24 km.) east of Quebec, stop abruptly at 587 

 feet (178-9 m.). A similar upper limit to wave-washed 

 deposits appears on the road running inland from St. 

 Joachim, 10 miles (16 km.) farther east, at about 570 

 feet (173-7 m -)- At St. Gervais, 15 miles (24 km.) south- 

 east of Quebec, a well built bar of gravel stands 632 feet 

 (192-6 m.) above the sea. These measurements harmonize 

 with those for the upper marine limit along the south 

 35063—4 



