14
GLACIATION

GENERAL STATEMENT

The glacial cycle in a mountainous region involves a development of
small mountain glaciers, an expansion of the ice-cover to an ice-sheet of
regional dimensions, in which the movement and extent of the ice are
controlled mainly by climatic factors and are largely independent of the
underlying topography, and a subsequent decrease of ice-cover to valley
glaciers and finally to small mountain glaciers (Kerr, 1934b; 1936; Davis
and Mathews, 1944). The regional ice-sheet phase of this cycle produces
erosional and depositional land forms distinctly different from those
produced by the valley and mountain glaciers that precede and follow it.
In Aiken Lake map-area, land forms produced mainly by valley and
mountain glaciers dominate the topography; the effects of a regional ice-
sheet are less conspicuous.

Tue CorDILLPRAN IcE-SHEET

All parts of Aiken Lake map-area were, apparently, covered by an
ice-sheet that moved across the mountains and over valleys to some extent
independent of the local topography. This ice-sheet was part of the
complex of glaciers and ice-sheets that covered most of British Columbia
during periods of Pleistocene glaciation, and which is generally referred
to as the Cordilleran Ice-sheet (Flint, 1947, p. 216). In Aiken Lake
map-area this ice-sheet deposited erratics at elevations up to 7,600 feet
(summit of peak between Lay Creek and Croydon Creek).

Investigations in various parts of northern British Columbia have been
accumulating evidence that there were at least two major advances of the
Cordilleran Ice-sheet, separated by an interglacial stage long enough to
enable extensive deposits of silt and gravel to be laid down in the lowland
areas, and to allow streams to erode channels in bedrock below the
glaciated level (Dawson, 1891; Malloch, 1910, p. 128; Johnston, 1926,
p. 147; Holland, 1940, p. 20; Lay, 1941, p. 16; Armstrong and Tipper, 1948,
p. 306; Armstrong, 1949, p. 14). Whether the ice completely disappeared
from the mountainous areas during this interval is not known.

There is ample evidence that the last major movement of the Cordil-
leran Ice-sheet over the map-area was toward the northeast. Glacial
strie and large groovings on peaks and crests of ridges, well above and at
an angle contrary to the obvious direction of motion of the valley glaciers,
trend north 30 to 60 degrees east. The most abundant erratics at high
elevations are of granodioritic rocks, whose only possible source is the
Hogem batholith or other intrusive bodies to the west or southwest. The
Uslika formation of Conglomerate Mountain has been the source of boulders
of characteristic conglomerate, which are widespread on the mountains and
tidges to the northeast to and beyond the eastern limits of the map-area. A
5-foot erratic of this conglomerate rests on a spur of the mountain east of
Wasi Creek at an elevation of 6,200 feet, higher than any present outcrop
of the Uslika formation itself. Nor were boulders of this conglomerate
found in any other direction from Conglomerate Mountain.