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114

» “The rock through which the petroleum ascends here is a heavily bedded,
greyish, rather coarsely crystalline, cavernous dolomite, and is entirely unlike
the bituminous beds south of the lake and down the Mackenzie, which in most
cases consist of calcareous shales. The dolomite is everywhere permeated with
bituminous matter, which collects in the numerous cavities, and oozing up
through the cracks, often forms small pools on the surface of the rock.

“Sulphur and tar springs are reported to occur at a point about half-way
between this and Fort Rae, but as I did not hear of them until I had left the
lake, I was unable to visit them. A tar spring is also known to exist under the
surface of the water in the deep bay immediately east of the Big Island fishery,
as many of the boulders and rocks along the shore in this neighbourhood are
coated with bitumen which has been washed ashore, and hummocks of ice stained
with the same material are cften observed. On the south shore bituminous
shales and limestones occur at several points.”

A range of hills composed of dolomite rises from the shore on the north side
of Sulphur bay which lies to the north of Windy point. Tar springs comparable
in size to those of Windy point are found on these hills at an elevation of 200
feet above the lake and a mile inland.

Some of the limestone in the Rock-by-the-river-side is slightly bituminous
and Franklin observed “sulphurous springs and streams of mineral pitch issuing
from the lower parts of the limestone strata” exposed in Bear rock.

McConnell states that “near Fort Good Hope several tar springs exist, and
it is from these that the Hudson’s Bay Company now obtain their principal
supply of pitch. The springs are situated at some distance from the river and
were not examined.”

The Devonian strata exposed on Athabaska, Peace, and Mackenzie rivers are
nearly horizontal. On Athabaska river and its tributaries there is some local
doming, and limestone is brought to the surface by an anticline between 35 and
40 miles up Mikkwa river, a tributary of the Peace.

A. E. Cameron, in, his report for 1917, describes the structure of the Devonian
system on Great Slave lake as follows:

“Stratigraphic studies have revealed the presence of a gentle anticline
stretching across the lake from Pine point on the south shore to Nintsi (Windy)
point on the north shore. On the south shore the apex of the anticline is shown
on the east side of Pine point and the lowest beds exposed show the Pine Point
series of bituminous limestones and limy shales. The presence of higher strata,
the overlying Presqu’ile dolomites, both to the east on Burnt islands and to the
west at Presquile point, clearly demonstrates the anticlinal structure. On the
north shore the crest appears to lie in the erosion basin of Sulphur bay. The
Presqu’ile dolomites are exposed on the east shore of Nintsi point, at various
points on the shores of the bay, and eastward to Jones point; whereas the over-
lying Slave Point limestones are shown on Slave point west of Nintsi point and
again near House and Moraine points northeast of Jones point.

“ Structural conditions suggestive of gentle anticlinal folding are noticeable
in the limestone outcrops on Buffalo river and those exposed on Hay river above
the falls. Exposures are confined to the valley floors when the rivers have cut
down into the Devonian sediments and on account of the overburden of glacial '
drift the extent of the folding was not observable.

1Cameron, A. E., Geol. Surv., Can., Sum. Rept., 19116.
2 Geol. Surv., Can., Ann. Rept., vol. IV, 1891, p. 31 D.