17

not much larger than at present. From the position of these abandoned
moraines and the size and form of the cirques, it is estimated that the
amount of ice was about twice as great when the moraines were formed as
at present. The rate of retreat of existing glaciers is believed to be rela-
tively slow; those above the regional snow-line are fairly ‘healthy’, filling
their cirques and vigorously eroding their basins, but those below about
7,200 feet are much less active, and are existing mainly on their remaining
ice mass (Plate IV B). Part of the glacier at the head of the main branch
of Abraham Creek has advanced slightly in recent years and ploughed
into its own moraine.

A conspicuous feature of the erosion by mountain glaciers in all parts
of the map-area is its asymmetrical character. The difference in the rate
of ice and snow wastage on north facing as compared with south facing
slopes is sufficient to concentrate the largest and most active glaciers on the
north and northeast facing slopes. As a result, ice erosion by mountain
glaciers has been almost entirely from the north and northeast. Ridge
divides have migrated southward, and the heads of many of the smaller,
east or west trending valleys turn southward (e.g., Jim May Creek). The
Lay Range is an outstanding example of a range whose divide has migrated
to its southwest edge, and whose main mass is deeply dissected by a series
of parallel, northeast draining, cirque-headed valleys (See Map 1030A).
Most of the valleys in the map-area have smooth, regular north or east
walls and deeply dissected south or west walls, breached by hanging
cirque basins and small hanging valleys. The general landscape has an
asymetrical wave-like appearance, with relatively gentle south slopes
and precipitous north slopes.

Deposition By Icz

The material carried by the Cordilleran Ice-sheet was probably mainly
deposited beyond the map-area. Except for erratic boulders on a few high
shoulders and balanced precariously on some of the ridges, it is probable
that all deposits of the ice-sheet have been covered, or reworked by, and
incorporated into, the deposits of the later valley glaciers.

Morainal deposits are abundant in all parts of the map-area. Those
in the valleys are largely intermingled with outwash. Each of the main
valleys contains bands of chaotic knob and kettle topography and of
recessional moraine. Well-formed recessional moraines, almost continuous
across the valley, are found in Osilinka River-Chudelatsa Lake Valley at
the south boundary of the map-area; in the west branch of Osilinka River
Valley upstream from the river forks; and in Mesilinka River Valley near
mile 76, Aiken Lake winter road. The depth of the drift in the valleys
varies considerably. In most places the ground moraine from the last ice
advance in the larger valleys is between 5 and 10 feet thick. Kettles in
non-stratified drift in Osilinka Valley above the forks, however, are 70
feet deep, and the recessional moraine at mile 34, Aiken Lake winter road,
reaches to 450 feet above the nearby, slightly entrenched, Osilinka River.
At the point where it leaves a through valley and cuts across the mountains
northwest of Uslika Lake, Vega Creek has been incised into more than
100 feet of drift.