estimated.

tore : -15-
detail the thickness of the conglomerate formation cannot be safely

For 10 miles south of Muncho lake, in streams entering the
lake from the east, and for 17 miles north of the lake along Trout
River, porcellanous shale, sandstone, and conglomerate are overlain by
coral reef limestone of Middle Silurian age. In many cases the out-
crops. are too small to map. Near the limestone contact are shales
full of worm burrows, and south of Muncho Iake some of the sandstones
are limy and contain fossils.

Near the contact, most of the clastic rocks approximate the
limestone in structural relations, but lower beds are quartzitic, and
resemble the Precambrian sediments in metamorphism and complexity of
structure. Near Toad River there is much uncertainty as to the
identity of the beds, but farther north they appear to belong to the
upper division of the Cambrian (7) series, as represented along the
west side of Muncho Lake’.

Along Trout River Valley the limestones dip westerly for
several miles north of Muncho Lake, and faulting along Trout River has
probably been responsible for their relationship with the Cambrian (7)
sediments, which rose as mountains west of the river. Such faulting
is known to have occurred comnonly in the nearby mountains.

The age of this sandstone-conglomerate group is pre-Middle ot
Silurian, as wherever observed the upper sandstone member is overlain
by a few feet of worm-burrowed shales and their closely associated
overlying coral reeflimestone. What the actual age of these clastic —
deposits is can only be conjectured from lithological comparisons.
Known Ordovician beds on Dease River consist of graptolite-bearing ©
shales, but Keele (1910) found on Gravel. River, in addition-to grap ~~
tolite-bearing shales, 4,000 feet of argillites and dolomites, sur-
mounted by a 100-foot diabase sill and 1,500 feet of sandstone, all

of which he places in the Ordovician. To the east the sandstone in-
creases toa thickness of 4,500 feet, the prevailing colour being
reddish.

ee oS In his Middle or Lower Cambrian, Keele, (1910, pages 37 and
38) ineludes 2,000 feet of conglomerate and 100 feet of coarsely
laminated hematitic and siliceous shale. i

In the light of available evidence the writer leans towards
the conclusion that the conglomerate and overlying sandstone of Muncho
lake and vicinity may be Cambrian. The group bears some Similarity in
stratigraphic relation and lithology to the Cambrian beds of Gravel
River and of Franklin Mountains.

Silurian and Devonian

A thick series of grey limestones with associated basal
shales and interbedded sandstones is exposed westward from the front of

(the Rocky Mountains. Along MacDonald Creek south of the Highway the
series rests upon the eroded surface of Precambrian slates and quartzites,

and a similar contact relation occurs along Toad River. Along the east
side of Muncho Jake-Trout River Valley, and on the west side of Muncho
lake, as already described, the limestone series rests on light-coloured
Cambrian (?) sandstone.

The upper contact of the series is conformable with overlying
shales of Upper Devonian age, belonging. to the next series to be des-
cribed.