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‘DARK SILTSTONES’
Definition

The provisional name ‘Dark siltstones’ was assigned by McLearn
(1947A) to a well-defined lithological unit lying between the ‘Flagstones’
below and the ‘Grey beds’ above. This unit is probably identical with
Hage’s (1944) ‘shale member’ of the Schooler Creek formation, the ‘upper
shale’ of some field geologists. It consists of from about 75 feet to more
than 450 feet of marine, dark, calcareous shale, dark, calcareous siltstone,
and dark, lenticular limestone. It encloses the Nathorstites fauna, which,
however, is not confined to it, but passes upward into the lower part of the
‘Grey beds’.

Peace River Valley

A good section, although not complete, of the ‘Dark siltstones’ is
exposed at the east end of the Beattie ledge, between Adams and Aylard
Creeks, on the north bank of Peace River (See Figure 8). It is overlain
conformably by the ‘Grey beds’. The lower part of the ‘Dark siltstones’
is concealed below river level at this locality. A section measured by
McLearn (19474) is as follows, in descending order:

Thickness
(A Feet 8)
roxim:
Overlying ‘Grey beds’ a a‘
Siltstone, dark grey and brownish grey, somewhat carbonaceous,

shalyscand’slabby sects. ac cire heytie i neltele es eseacie ee ertciera.e 300
Siltstone, dark, somewhat carbonaceous, fissile; and shaly and

lenticular dark limestone; with the Nathorstites fauna...... 30
Siltstone, dark grey, brownish grey, somewhat carbonaceous,

calcareous, shaly; and some limestone.................--- 100+

Far up Folded Hill Creek (See Figure 8), between Brown and Folded
Hills on the north side of Peace River, are exposures of shales and dark
calcareous siltstones. They are overlain by the ‘Grey beds’ but their
lower limit is unknown. They carry poor fossils, including Daonella sp.,
and are probably part of the ‘Dark siltstones’.

Halfway River Valley

In the Fourth Gully on Mount Wright (See Plate III B), the Triassic
beds are almost flat-lying, and higher and higher strata are met with as the
gully is traversed toward its source. In this gully, between the top of the
‘Flagstones’ unit below and the base of the ‘Grey beds’ above, are about
300 feet of dark, shaly siltstone, limestone, and shale with the Nathorstites
fauna. To the west, these beds extend along the cliff on the north slope of
Mount Wright, and there, changing to a steep west dip, extend down the
Third Gully of Mount Wright, where they are well exposed and have the
same lithology as in the Fourth Gully and carry the same Nathorstites fauna.

The beds of this unit have also been observed on the south side of
Halfway Valley west of Mount Wright.

Sikanni Chief River Valley

The strata of the ‘Dark siltstones’ are well exposed in the bottom, and
on the lower part of the east side, of the valley of Hage Creek, which drains
the west slope of Mount Hage on the south side of Sikanni Chief River