37

Unconformity at the Base of the Slide Mountain Series

With regard to the relationship of the Cariboo and Slide Mountain
series Bowman! makes the following statement: ‘These gold schists (Cari-
boo series) are much more highly altered than any of the rocks in the Bear
River series. Their junction as observed on Antler creek, below Pleasant
Valley creek, exhibits, however, a similarity of strike and dip suggestive
of conformability. But the greater degree of metamorphism is apparent
at a glance, and is alone good evidence of their greater age. . . . The
presumption is that they constitute some part of the lower Palzozoic—
perhaps even pre-Palzozoic—system.”

Reference to Bowman’s geological map and to that accompanying
this report will show that the line of junction of the two series as mapped
by Bowman lies within or near the western edge of the Barkerville form-
ation of the Cariboo series. Bowman included the massive outcrops of
the Barkerville limestone in this vicinity in his Bear River series, and
thus failed to recognize the actual position and character of the break
between the two series. As a matter of fact, this stratigraphical break is
not evident along Antler creek owing to a covering of drift and vegetation;
but it may be readily examined along the southwestern slope of the ridge
extending from Antler creek to Summit creek.

Bowman’s general conclusion regarding a probable unconformity is
substantiated, since such a stratigraphical break has been found to be
continuous for at least 12 miles beyond the northeastern corner of Barker-
ville map-area.

The evidence of the unconformity may be summarized as follows:

(1) There is some discordance of strike and dip between the two series.
Discordance of strike is shown on the geological map due west of mount
Murray, where the Guyet formation lies across the contact of the Barker-
ville and Pleasant Valley formations. Discordance of dip is shown on the
geological structure sections.

(2) The Guyet conglomerate rests on an erosion surface of the Cariboo
series, and contains pebbles and boulders of the underlying formations of
that series. The basal part of this conglomerate is clayey and somewhat
schistose, and appears to grade into the underlying slate and schist. This
part, therefore, is the result of the metamorphism of an old residual mantle
of clayey decomposition products.

(8) Pebbles of folded, crenulated, slaty, and schistose rocks in the
conglomerate are proof of the metamorphism of the Cariboo series before
the deposition of the base of the Slide Mountain series. Pebbles of medium-
grained intrusive rocks indicate that erosion removed a considerable
thickness of the underlying rocks before the formation of the conglom-
erate

\4) There is a decided difference in the degree of metamorphism to
which the rocks of the two series have been subjected. The Cariboo series
is characterized by quartzite, slate, and schist, whereas the Slide Mountain
series is made up of indurated shale, chert, and massive fossiliferous lime-
stone.

10Op. cit., pt. C, p. 28.