87

that latitude the trend of the ranges changes and they swing in a wide circle te
the westward round the upper branches of Peel river. On Wind river the moun-
tain-building forces have been less intense and the structure is characterized by
open folds with comparatively low dips to the beds. The strike of the ranges is
here east and west.

Richardson mountains, which separate Peel river from the Porcupine, have
a north and south trend. They have on the whole an anticlinal structure, and
are broken by longitudinal faults. On the eastern side they present a steep fault
face to the delta of the Mackenzie, and the beds undulate gently. In the middle
of the range the dips increase to 70 degreés but maintain an easterly direction,
and on the western side the beds gradually flatten and finally dip westward. As

the range approaches the sea-coast the strike of the beds assumes a more westerly —

trend.

ECONOMIC GEOLOGY
BITUMINOUS SANDS

General Description

An immense body of bituminous sands, the so-called tar sands, is exposed on
Athabaska river. It extends from near Boiler rapid, about 200 miles below
Athabaska, to a point many miles below McMurray. Outcrops occur also in the
banks of the rivers, and small streams tributary to the Athabaska between these
points.

The bituminous sands vary in colour from grey to dark brown or jet black,
according to the quantity of contained bitumen and depth of weathering. Where
they are heavily saturated they are much softened by the heat of summer, and
the bitumen issues from the sands and forms pools. It is believed that they
consisted originally of unconsolidated sands and soft sandstone ranging in
texture from a fine silt to a coarse grit, and induration has been effected by
impregnation with bitumen. The formation contains occasional lenticular beds
of ironstone and quartzite and thin seams of lignite. The lower part of nearly
all exposed sections consists of unstratified sands and the resulting bituminous
sands are fairly homogeneous (Plate XII A). “In passing upward, however,
narrow bands of sandstones and occasional quartzites are found interbedded with
the originally uncompacted sands (Plate XII B). These non-bituminous strata
gradually increase until by their preponderance they entirely replace the bitu-
minous sands.”! The formation is overlain by the Clearwater shales, from the
first exposure at Boiler rapid down to McMurray. It constitutes the basal
member of the horizontally disposed Cretaceous series in this region, and rests
directly on the Devonian limestone with very little unconformity to mark the
great lapse of time intervening between the deposition of the two. The bitumen
with which it is impregnated is believed by many to have had its origin in the
Devonian formation.

“ Other occurrences in the province of Alberta have been recognized near
Bonnie Glen (N.W. 4 sec. 14, tp. 47, range 27, W. 4th mer.); Nakamun (N.E. 4

1 Ells, S. C., “Preliminary report on the bituminous sands of northern Alberta,” p 6.

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