22
Antler Formation

Distribution. The northeastern corner of the map-area is largely
underlain by this formation, which trends southeast from Two Sisters
mountain to mount Howley. It overlies conformably the Greenberry
limestone throughout most of its extent, and outcrops prominently along
Antler creek below its junction with Grouse creek; on the top of mount
Howley; on the western slope of Slide mountain; and on the top and
western slope of mount Murray.

Iithology. The rock types are greyish-green indurated shale (argil-
lite) and grey to white chert, with minor amounts of red indurated shale
and jasper, and some silicified or cherty quartzite. The individual layers
of chert and shale are usually from 3-inch to 2 inches thick, with an
average of about 1 to 1} inches. They exhibit remarkable continuity
along the strike, and in places are much crenulated. The chert and
shale are commonly interbedded.

There is very little evidence of metamorphism in these cherts and so-
called argillites. The latter are fissile, parallel to their stratification, but
they show no parallel development of mica plates, which is characteristic
of slate and argillite. The fissility which they possess is a primary
bedding structure and is not due to flow cleavage. Considerable attention
was paid to this formation to determine the character of the fissility men-
tioned above and to discover whether the chert was an original deposit or
a replacement. Only in one small exposure was there any evidence seen
of a quartzitic or fine conglomeratic fabric partly replaced by chert ; in all
other cases, the chert appeared to be a primary deposit. Some of the
shale beds are not only indurated, but are somewhat cherty, which gives
them a marked hardness.

Age and Correlation. Similar formations of interbedded chert (called
cherty quartzite) and indurated shale (called argillite) are characteristic
of the lower part of the Cache Creek and equivalent series in British
Columbia. Dawson! describes a similar formation in the western part of
the Kamloops map-area as follows: The cherty quartzites “‘oenerally
occur in well-defined beds of a few inches only in thickness and often form
great masses of strata. They are very fine grained, resembling hornstone
or chert, usually grey in colour, passing to black in one direction and to
yellow-grey and nearly white in the other, but occasionally greenish-grey.
Almost everywhere they are traversed by innumerable veinlets and threads
of white quartz. The bedding planes are often black and lustrous, and
black, glossy argillite-schist is frequently associated with them. These
rocks have evidently been silicified subsequent to their deposition, but
perhaps very soon after, for it is pretty clear that they were much in their
present condition before the main period of disturbance by which the
formation has been affected. ... .

“The argillites are generally hard and dark-coloured, ranging from
black to grey. They are often schistose and sometimes show more or
less slaty cleavage. In some places they are largely siliceous and evince a
tendency to pass into the cherty quartzites.”

1Geol. Surv., Canada., Ann. Rept., vol. VII, pt. B, pp. 40-41 (1895).