Nechako River Map-Area

are on the northeast slopes of hills and mountains and cover the adjacent valley bottoms. They commonly lie with their long axes at right angles to the last direc- tion of ice movement. The valleys and low areas generally have a low gradient, or a constriction or obstruction that would impede the easy flow of ice. Without the pressure of an ice-cap or the influence of a steep gradient and in areas less exposed to the sun the ice melted in situ.

The northwest half of the map-area is in sharp contrast. Sharply defined drumlins and rock drumlins are common, eskers and kettles are less common and smaller, and little topography characteristic of ablation moraine exists. Ap- parently no large mass of ice stagnated there.

Glacial History

The glacial cycle of a mountainous region according to Kerr (1934, p. 22) is believed to go through four stages: (1) alpine, (2) intense alpine, (3) moun- tain ice-sheet, and (4) continental ice-sheet. Nechako River map-area, although mountainous in part, is more typically a plateau area, and is therefore an area into which ice moved rather than one in which it initially accumulated. Although there are a few cirques that have been overridden by ice, it is unlikely that the Pleistocene ice-cap had its beginnings within the area. Indeed there are so few cirques, either preglacial or post-glacial, that the writer believes that little ice accumulated within the area while any hills or mountains remained above the

| ice-sheet, but rather that it accumulated in the Coast, Omineca, Cariboo, and

Rocky Mountains and flowed into the Interior Plateau as piedmont glaciers that coalesced to form an ice-cap. As the topographic features of Nechako River area were covered, accumulation on the ice-cap itself began, reaching thicknesses probably well in excess of 6,000 feet. The direction of flow at the glacial maximum is not clearly indicated but it is possible that the ice flowed in general outward from the centre of the province and that many shifts in the position of the ice divide occurred. In Nechako River map-area the north-south grooves on some higher hills indicate that the ice moved from north to south or south to north. Whether this was at a time of maximum ice thickness is unknown; it was earlier than the last movement.

The last movement of ice across the area was from the southwest and west, and apparently at that time the ice was still thick enough to flow over all or nearly all topographic features, although it was thinning rapidly and the topo- graphic features were exerting greater control on the manner of flow. Ice flowed around some hills and mountains such as Fawnie Range, but elsewhere, such as around Nechako Range, it thinned, broke into separate masses, stagnated, and melted in situ.

In most major valleys not parallel to the direction of ice movement, such as Chedakuz, Euchiniko, and Blackwater, there is no evidence of ice moving along the valleys; in other valleys, parallel with the direction of ice movement, there is no evidence to suggest valley glaciation. In the southeast half of the

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