Whitesail Lake Map-Area

These ridges and grooves appear to be best developed where the ice
pushed uphill. This is well illustrated on the west slope of Chef Ridge
where the ice pushing upwards out of the valley of Eutsuk and Whitesail
Lakes rode over the top of the mountain. The markings there show identical
trends on both sides of flat-topped Wells Gray Peak suggesting that the ice
rode over the top of the peak without change in direction. To do this the
ice must have reached a thickness of at least 4,400 feet.

In timbered country the ridges are characterized by a good growth of
lodgepole pine and at timber-line by stunted spruce and juniper. Most of
the adjoining depressions are marked by a long narrow lake or wet meadow.
Many of the lakes in the plateau area are pointed towards the east, or in the
direction of ice flow.

The size and shape of the ridges vary considerably. They may be long
and narrow, between 1 mile and 2 miles in length and a few hundred feet
wide, or they may be oval in shape from 4 to # mile long and 3 mile wide.
Commonly they are # to 1 mile in length and less than 1,000 feet wide.
Height may be as much as 50 feet, but is commonly less. These compare
with the drumlins observed by Armstrong (1949, p. 12)1 in the Fort St. James
map-area.

Many of the ridges show crag-and-tail effect with the tail towards the
east, and rock outcrops at the crag end. Where no rock outcrops Armstrong
and Tipper (1948, p. 293) suggested that the hard core causing the ice to
ride upwards was a frozen mass of till with softer material on the sides.

The ridges are composed largely of fairly well-rounded pebbles and
boulders in a grey to light brown or sandy clay, and may in places contain
some outwash material.

For the origin of such ridges and grooves Armstrong and Tipper
postulated the presence of an earlier till plain over which the final advance
of the ice proceeded. However, Gravenor (1953, p. 679) considered only
one advance necessary and that such drumlins may be due to both destruc-
tional and constructional processes. According to Gravenor, it is not neces-
sary to have a previous ice advance and consequent till layer. The advancing
ice itself might have a layer or load of till in front of it, particularly if the
advance is slow. The ice would then ride over this till and fashion the
drumlin-like ridges. In areas where the overburden is deep, on the other
hand, the ice might erode the drift into the drumlinoid shapes. In the
Whitesail Lake area similar forms were commonly the result of constructional
processes. The advancing ice has ridden up and over a rock outcrop or

1 Dates in parentheses are those of references cited at the end of this report.

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