Rib pa

thought to be Upper Devonian in age as described below.

Another fossiliferous horizon in dark grey limestone was
found near a temporary bridge over Racing River (former mile 133; the
present road crosses 2 miles lower down stream). The following Middle
Devonian fossils are recognized: Reticularia modesta (Hall), Meristella
sp., Schuchertella sp., Odontocephalus sp., and undetermined corals.

The base of the Devonian limestone has not been determined,
and its thickness is not know. i

Devonian and Mississippian

A thick series of dark shales occurs over large areas adjoining
the Highway west and north of the front range of the Rocky Mountains.
The basal beds outcrop near mile 109, as described above. A few inches
above the Middle Devonian coral reef limestone, thin beds are packed with
tiny fossils that correspond exactly with illustratiocus of Tentaculites
spiculus Hall as found in Chemung shales of New York and Pemsylvania .
Two feet above the contact a poor specimen of Meristella? was found.
Elsewhere soft black shales are faulted against Silturo-Devonian liméstone,
or appear to lie above the limestone, Dcwn MacDonald Creek, along Racing
River, and particularly in Liard River Valley, dark shales of variable
hardness and black limy shale occupy large areas, and weather into valleys
or rounded, subdued hills, generally with a brownish cast, Some of the
shale weathers into soft mudstone; some outcrops are laminated; some have
sandy and limy lenses; and still others are very hard and slaty. A few
poorly preserved fossils have been found slong MecDorald Creek and in
Liard Valley and these suggest a Mississippian age for the containing
bédse Upper Devonian fossils were also found in basal shale beds near
mile 109. The general character of the series suggests a correlation with
the Minnewanka and Banff formations of the southern Rocky Mountains, the
Minnewanka limestone being Upper Devonian and the Banff shales Missis-
sippian.

Dark shales with conglomerate and sandstone beds and sandstone
lenses occur at the mouth of Dease River and above ‘and below Lower Post
on Liard River. No fossils have been found in these and their inclusion
in the Devono-Mississippian series is based upon their assumed position
above the Siluro-~Devonian limestones and the general similarity of the
shales to those ‘of the eastern sections. On the other hand, Dawson found
Ordovician graptolites in dark shale about 12 miles up Dease River, and
it is possible that the shales from the vicinity of Irons Creek and west
are of pre-Devonian age. A critical area extends 18 miles west ‘of Irons
Creek. An intensive search for fossils in the shales in this area might
provide the necessary evidence.

The best known basal beds of shale, as described above, overlie
Middle Devonian coral reef limestone. The contact is sharp and may be
disconformable, as a lapse in time is indicatcd by the Fossits contained
above and: below the contact.

Other exposures of shale are described below, in the order of
their occurrence from east to west

At the front of the mountains, about 500 jards east of mile 101,
black, fissile, "pencil" shale stands vertically against the east
“vertical limb of grey Silurian limestone. The shale weathers rusty yellow,
iron sulphate appearing on the surface. It shears in square "pencils" and
plates. Eastward of mile 100, black shale of varying character, including
hard sandstone beds, passes upward into fossiliferous Triassic sandstone
and limy shale. The age of the fissile shale in faulted relation with the
front Timestones of the mountains remains in doubs. T% may be Devonian, é

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