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MESOZOIC (?) RECORD
Mount Murray Epoch

The next event in the historical sequence was the intrusion of the
Mount Murray basic sills and dykes into the cherts and shales of the
Antler formation. There is no field evidence regarding the date of these
intrusions. Since the sills are sliced by the cross-range faults which were
the aftermath of folding, it is probable that their intrusion took place
while the cherts and shales were still horizontal. The age of the sills has
been tentatively given as Jurassic, thus correlating them with the period
of the intrusion of the Coast Range batholith.

Epoch of Deformation and Erosion

Following the intrusion of the basic sills, the country was again com-
pressed by orogenic forces and formed into a broad anticline whose axis
extended along the same course as that of the previously formed anticlinal
structure. In this case, however, the folding was not intense, and the
Slide Mountain series and associated Mount Murray sills were not met-
amorphosed. Following this folding or differential elevation of the country,
a tendency for the uplifted formations to settle down again exerted itself,
and found expression in the block-faulting of the formations along north-
easterly trending fissures. Many of these adjustments took place along
the planes of the “B” veins, which yielded by the fracturing of their
quartz, pyrite, arsenopyrite, and sphalerite, and the flowage of their
galena.

A long period of erosion succeeded this deformation and resulted in

the peneplanation of the country possibly in late Cretaceous time. Upwards
of 15,000 feet of strata were removed from the axial part of the anticline,
thus exposing the hard, massive quartzites near the base of the Richfield
formation.

TERTIARY AND QUATERNARY RECORDS

The Tertiary record is very incomplete, and it is difficult to determine
just what features of the present topography should be referred to this long
period whose record in the area appears to be very largely that of erosion.
In the lower part of Quesnel River basin and along Fraser river west and
northwest of Barkerville area, there are extensive and thick Tertiary
sediments overlain in places by lava flows. The upper surface of these
sediments near Quesnel stands at about 2,500 feet. Barkerville area was
the source of part of the sediments, for the drainage of the area is towards
the Tertiary basins, and as the lowest parts of the present bedrock valleys
are about 3,700 feet, it is possible the valleys were eroded to within a few
hundred feet of their present depth in Tertiary time. This amount of
erosion, however, is small as compared with that of many other parts of
the world where thousands of feet of strata are known to have been deposited
and again eroded during Tertiary time. It may be that the Tertiary
lava flows in this general region were formerly much more extensive than
the present remnants seem to indicate, and that much of Tertiary time was
consumed in erosion of the lavas without greatly eroding the underlying
rocks. The depth of erosion of the valleys and the occurrence of deeply