69

J. A. Allan states that he did not observe the Bearpaw formation in the
parts of this plateau examined by him and that if it exists it does not exceed 100
feet in thickness.1 Some distance below the Edmonton formation there are beds
of freshwater origin containing seams of coal. These are given the local name of
Sawbridge formation.

Martin mountain, which lies northeast of Lesser Slave lake and is 1,000
feet high, is composed largely of sediments that may be equivalent in part to the
Edmonton in age. Fragments of lignite and sandstone are abundant on its lower
slopes and a loose fragment of sandstone found at its base afforded specimens of
freshwater shells.

The Cretaceous sediments of Athabaska river are nearly horizontal and rest
upon the Devonian with an unconformity so slight that it can be detected only
by examination of the contact for a distance of many miles. Between Grand
rapids and Pelican rapids the dip is about 53 feet per mile south. Between.
Pelican rapids and Athabaska the dip is about 10 feet per mile. This greater dip
may be due, in part, to its southward direction, and may indicate that the true
dip of the Cretaceous strata on the Athabaska is west of south. A low anticline
crosses the river near Crooked rapids; the dip on each side is only 3 or 4 feet a
mile. Below McMurray the strata are probably nearly horizontal and may have
a slight north or northeast dip.

The Cretaceous sediments exposed on Peace river rest upon Paleozoic rocks
on the lower part of the river and on Triassic rocks near the Rockies. The
following descriptions of the formations exposed on Peace and Smoky rivers are
taken almost verbatim from reports of F. H. McLearn appearing in the Summary
Reports of the Geological Survey for 1917 and 1918.

Loon River Formation. The Loon River shales are exposed on the valley
sides from Vermilion chutes to near Brown’s trading post, and north and east
of the great horseshoe bend underlie the plateau adjacent to the river. They
consist of dark blue to dark grey, friable weathering shale with a few rounded
or flattened ironstone concretions. To the south, where they are penetrated by
the wells of the Peace River Oil Company, they aré more arenaceous, particu-
larly near the base. Thus, in well No. 1 the following section rests on the lime-
stone.

Feet.
Sia Oe ae ee ee ee SE EEE ORR IDE APSE Bu oars Face otal al shee, ie Wits BNR
CR AAALONC 5s NT Ee me SO eae Ft eed cad ea s- easier Oo
STEN Ce tee eee RR ae ne pe a Perel cay enna es er Gees Crates SCONES Rar « 53
ATI SCOM Go ee a ie Se ae tee oem one mel iene fe) ae Pel sinh oh skeen nays oes igi eten) 65
Girlie. 1. . SG iOdc). Sets) Bilt O. Beks Ons, Se Roe
Sandstone co as ee ey he ek eo ees peers euler pe urecers Ss sete FPS 26
Shale with concretions and bands of ironstone... .. .. .. «+ ++ -+ =; 51

PAI LOZOIG HMESTOMNGS 5p ities a tole totes oe rete tase nace ae gt —_—

Tn No. 2 well, about 13 miles south of No. 1, the 70-foot bed of sandstone
has increased to 106 feet and the 53-foot bed of shale has decreased to 14 feet.
Both wells also show a number of smaller beds of sandstone in the upper part of
this formation, which are not present in the exposures downstream. Along the
upper contact with the Peace River sandstones there is much replacement laterally
of sandstone by shale, so that the contact rises stratigraphically northward. As
exposed on the river in the north the even bedding and marine fossils point to 2
marine origin. It is possible, however, that the thick sandstones near the base

1 Geol. Surv., Can., Sum. Rept., 1918, p. 11 C.

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