|

limy beds is in most places parallel to the bedding. Some of the beds,

Be

Age Character Thickness
_ Feet
| Ta
Pre-Middle Silurian Grey sandstone and red | ae
(Cambrian? ) | conglomerate [POO \¢

Precambrian — Dolomite, slate, and
quartzite, cut by }
| basic dykes i  2,000%

Precambrian

The oldest formation traversed includes the most highly

, metamorphosed strata of the region, and is the only formation known to

be cut by intrusive rocks. It is best developed along Toad River, but
is well exposed also along MacDonald Creek. Whole mountain groups
composed of these rocks are yet to be explored in the headwaters of
MacDonald Creek, up Toad River southwest of the Highway, and: PE ea
west of Muncho Lake north of Gundahoo Pass,

In the type section on Toad River, near the Highway. crossing,
highly folded, light-coloured quartzite and porcellanous argillite and
slaty rocks rise 600 to 1,000 feet from the valley floor and are overlain
by” nearly flat-lying grey limestone containing reef corals of Middle

Silurian age. The contact is everywhere marked by an angular unconformity «

Mud-cracks and ripple-marks are well defined in the argillites, which are
generally limy and locally contain small mud balls. The cleavage in the.

however, consist of bands of quartzite and grey slate, and in these the’
cleavage is independent of the bedding planes. Colours vary from light
yellow or gréen to dark grey, and the formation generally wee thers dark
‘brown e i

The poten on the quartzite are well marked. At one Locality
ripple-marks of g inch amplitude are overlain by current ripples 1s inches
in amplitude. The variability of the sediments and their mud-cracks and
ripple-marks indicate near-shore conditions ina See Ne is that Was. receiving
sediments fron a fluctuating source of supply. :

About 300 yards southeast of the bridge over Racing River an
irregular diabase dyke cuts light-coloured quartzite and porcellanous
argillite. The dyke averages about 15 feet in width and is apparently

vertical. The dyke rock is hackly fractured and is cut by seri iaoee ele

North of Toad River and the Highway, between miles 156 and 157s,
five 50-foot vertical dykes cut the quartzites and associated rocks and
extend upward to the top of the formation, or to an elevation about 1,000
feet above the valley. These dykes were studied in the field and examined
under, the microscope by J. DeLeen who reports as follows:

"Two thin sections were examined; they are from a dyke 50 feet
wide in fine-grained grey limestone. One section from the centre of the
dyke shows a maximum grain length of 1 millimetre. About 50 per cent of
the rock is plagioclase (AbgAng) that is now largely altered to carbonate.
About 30 per cent of the rock is hornblende that is partly converted to
chlorite, and there is not over 2 per cent quartz, about half of it inter-
grown with feldspar as micropegmatite. Disseminated grains of magnetite