115

“ Ag shown by the oil seepages and tar pools on Nintsi point the Presqwile
dolomites appear as the most probable oil horizon of the district and as these
sediments are exposed on the limits of the anticline, the possibilities of an oil-
producing field existing on the shores of the lake are not very great.

“A thick series of soft clay shales is exposed on Hay river, which from
the stratigraphical relation would appear to overlie the dolomites. If the dolo-
mite horizon can be found elsewhere in the district under suitable structural
conditions and overlain by these impervious shales it may be worth investigating
with a drill.

“ On Hay river, above the falls, limestone outcrops in the valley show gentle
undulations forming anticlines and synclines of a low order. The limestones
here exposed represent upper members of the Hay River limestones which overlie
the thick series of shales above mentioned.

“It is to be noted that the section exposed on Peace river shows members
of the Simpson shale series unconformably overlying the gypsum series of upper
Silurian age, and thus the middle Devonian section as exposed on Great Slave
lake is here absent. It is, therefore, possible that the dolomites would not be
found underlying the shale series in the folded area above the falls on Hay
river, or, if present, they would probably be somewhat thinner in their develop-
ment than is shown on the shores of the lake. If drilling operations were. con-
ducted on Hay river, a thickness of about 1,000 feet of sediments would have to
be pierced before the Presqu’ile dolomites would be reached.”

Details of structure in the Devonian formation below the point where the
Mackenzie reaches the mountain system have not been worked out. Anticlinal
folds are common and enter into the structure of such features as the Rock-by-
the-river-side and the several ridges that trend east and west in the vicinity
of the mouth of Carcajou river. The structural features of Franklin and Bea
mountains conform in a general way to the trend of Mackenzie mountains and
it is not improbable that local undulations occur in the intervening broad valley
through which the Mackenzie flows.

A few borings have been made into or through the Devonian limestones and
shales on Athabaska river, but no petroleum has been struck. Below McMurray a
number of wells have been sunk on local domes; at McMurray and 9 miles below
MacKay, wells have penetrated to the Precambrian rocks, and a short distance
above Pelican river on the Athabaska a boring was carried through the Creta-
-ceous and 1,000 feet into the Devonian. In the last well a flow of gas was
encountered at a depth of 2,040 feet. At Vermilion chutes a well was sunk to a
depth of 860 feet through Devonian strata. The few borings that have been made
have not given encouraging results, but the field for exploration is exceedingly
broad.

Cretaceous. The most striking surface indication in the section of country
underlain by Cretaceous rocks is the enormous deposit of bituminous sand occur-
ring at the base of the Cretaceous sediments on Athabaska river and its. tribu-
taries. This bituminous sand is described elsewhere in this report. :

A spring of natural gas is situated at Tar island on Peace river about 25
miles below Peace River Crossing. The gas rises with salt water and some tar
from among the gravel and boulders at the upper end of the island: ~The flow
of gas has been roughly calculated to be about 3 or 4 cubic feet per minute.’

Ga Pence river and around Lesser Slave lake bitumen has been found at a

1Camsell, C., Geol. Surv., Can., Sum: Revt.. 1946. <0