137 
masses which have offered unusual resistance to this ice 
action, indicate the directions in which these glaciers moved. 
The course of the one which produced the basin of Lake 
Ontario, was from the north and north-east toward the south 
and south-west. The Lake Erie glacier moved in the line of 
the major axis of the lake, from east to west, or more 
accurately, from north 75° east to south 75° west. The is- 
lands at the western end of the lake, are remnants of the hard 
Corniferous limestone beds raised in the line of the great 
Cincinnati anticlinal. These interposed considerable resis- 
tance to the action of the glacier, and portions of them were 
left, forming the islands, which are grooved, fluted and 
planed on all sides by the moving ice. The Lake Huron 
glacier had a course nearly north and south; that of Lake 
Michigan moved from the north with a direction a little west 
of south. On the rocky margin of Lake Superior, the 
scratches indicate a motion of the ice-mass from the north 
and north-east. The direction of the glacial strize about the 
more northerly lakes, Lake of the Woods, Slave Lake, Great 
Bear Lake, etc., has not been accurately ascertained. 
The geographical relation of this series of basins to the 
Canadian Highlands is not accidental, but is significant of 
their mode of formation; and there can be no reasonable 
doubt that each of them was excavated by a glacier descending 
from the Hozoic highlands, and ploughing into the plain 
by which these are surrounded. All the region about 
the Great Lakes was once covered by a moving ice-sheet, 
or continental glacier, which over-rede and _ disregarded 
all minor irregularities of the surface. This great glacier 
existed during the maximum of cold; and the effect of such 
an agent would be rather to obliterate than to form local 
basins. In the earlier part of the ice period, however, it is 
probable that the excavation of the lake-basins was begun 
by local glaciers, and again resumed and. completed by the 
same agency at a later period, when the amelioration of 
climate had caused the continental ice-sheet to disappear. 
Still later, when the glaciers which had filled and formed the 
separate lake-beds, were melted away, a great inland sea 
occupied the general basin of all the lower lakes. Of this sea, 
the shore lines are easily and widely traceable, and they are 
now known asthe old lake ridges or beaches. At one period 
in the retreat of the glaciers, they capped the Canadian High- 
lands, and formed the northern shore of this inland sea. 
From this ice-wall, masses were from time to time detached 
and floated away southward, carrying loads of boulders and 
11.—10. 
