aie

In the bottom of MacDonald: Creek ond in the westerly facing
cirque mentioned above, quartzite and slate rock of grey to. reddish
colour forms the basal formation upon which the limestone mountains
rest. These metamorphic rocks dip at high angles, and on their bevelled
edges, and ot various elevations, rest grey limestones of coral reef. -
origin. The corals are Middle Silurian in age, Halysites catenulatus
being most easily determined among the silicified forms. Upwards from
this unconformable base, rise 2,000 to 3,000 feet’ of light grey lime~
stone with at least one massive member of hard grey sandstone nearly 70
feet thick. The upper limestone members appear in general to be un-
fossiliferous. On the western side of the front range, however, near
mile 109, black shale overlies grey coral reef limestone as seen in the
falls of a mountain stream. Corals and a trilobite pygidia represent a
Middle Devonian age for these beds. No boundary has been found between
the Silurien and Devonian members of this limestone series.

“ Overlying the Middle Devonian limestones of the Rocky Mountain
belt are fissile black shales. At the contact near mile 109 mentioned
above, these shales are rusty weathering and are full of Tentaoulites —
spiculus Hall (7). Two feet above the contact a poorly preserved
Weristelle ? was found. Thus the lower beds of the black shale forma-
tion may be Upper Devonte possibly Chemung, in age.

Farther to the northwest, down the valley of MacDonald Creek,
the bordering hills are low-and wooded and rock formations consist of
black shale, argillite, black chert, and dark-coloured sandstone. These
soft weathering rocks are dominant to the junction with Racing River and
overlie limestone westward up Toad Valley as far as mile 143. In general
these shales are wfossiliferous, but in the hills to the east of mile
116 poorly preserved fossils probably represent Michelinia, and the
following genera are recognized: Productelle, Martinia, Athyris, and
Euomphalus. The general impression conveyed is that of a Mississippian
ge, and the shales strongly resemble the Banff shales of the Rocky
Mountains farther south. As already described; the shales weather
easily and are eroded into’ rounded hills and valleys. They will be
referred to eae as owe atone. pEouy: and a ‘Rivers. -

Mountains peor of Silurtén ae Devonian imestone’s appear
here and there from Racing River westward, rising through their over-
burden of dark Devono-Mississippian shales. From mile 143 westward up
the narrow valley of Toad River, such limestone peaks are dominant.
Between miles 152 and 158, however, older quartzites and slates show
here and there in the flanks of the mountains, and form the peaks south
of Toad River from mile 154 to 159. Along the Toad these metamorphic
formations are steeply folded and are cut by irregular basic intrusions -
and a series of vertical dykes averaging about 50 feet in thickness. An
unconformable relationship with overlying Middle Silurian coralline lime-
stone is clearly seen in the valley wall, The metamorphic rocks are
presumed tobe of Late Precambrian, Protérozoic age. The mountains south
of the Toad, and those flanking its upper valley, are high -and of for- on
midable aspect.

At mile 159 the Highway turns nearly due north and follows a
large valley: ‘occupied in the south by the upper waters and lake ex-
pansions of Toad River and to the north by a small stream flowing into
Muncho Iake. Northward, Muncho Lake extends for some. 10 miles &nd is-
drained by Trout River through a continuation of the same mature valley,
which takes a northwest by north course to join the trunk, east-west
valley of Liard River. The northerly trending valley, thus delineated,
is practically on the prevailing strike of the mountain structure. The
Highway follows it for 50 miles, and, as previously stated, the valley
extends for an undetermined distance southward to the headwaters of Toad
River. It is quite apparent that the valley of Toad River for 30 miles