33

quartzite members of the Richfield formation outcropping along the crest,
and the Slide Mountain series and Mount Murray sills acting as competent
horizons. These horizons are characterized by simple, large-scale, open
structures and a general regularity of strike and dip. Between them occur,
as the incompetent parts of the structure, the slates and associated rocks
of the Pleasant Valley formation, and the thinly-bedded, argillaceous, and
schistose members of the Richfield formation. These incompetent horizons
are characterized by pronounced drag-folding with very wide variations
in dip (Plate XIII). The black line pattern used on the geological structure
sections represents an attempt to picture the character and intensity of the
folding in each formation.

Even the competent horizons, particularly the Barkerville formation,
afford evidence that, although they control the intimately dragged structures
of the incompetent horizons, their own beds are somewhat drag-folded
indicating that, with respect to still larger geological units involved in the
folding, they themselves were somewhat incompetent. This statement
may be well illustrated by reference to Figures 3 and 4 and Plates X and XI
which show intimately drag-folded parts of the Barkerville limestone.
During the folding this rock must have been incompetent relatively to some
larger and more resistant unit, and it yielded first by drag-folding and
recrystallization. This deformation had the effect of thickening the lime-
stone and rendering it more competent and more capable of transmitting
the thrust over broad areas. To this thrust the more thinly bedded
quartzites and argillaceous rocks yielded by close folding and recrystalliza-
tion into schists and slates (Plate XII). Zones of intense crumpling and
shearing developed in these softer rocks and became partly mineralized
with quartz (See Map 2046).

With regard to the relationship of the thickness of the formations to
their structures, Bowman! makes the following statement: ‘As it would be
unsafe, where the rocks are so frequently on edge, to draw conclusions
regarding their thickness from any general section, however accurate,
attention may be directed to the following distances on the Cariboo map,
where a constant dip in the same direction was observed. On Williams
ereek such uniformity occurs for 5 miles; on Antler creek it occurs for 44
miles. ...In Devlin’s diggings at the foot of the Williams Creek
section, and again at Mink gulch above Richfield, the attitude is vertical.
Above these points are seen the usual gentler northerly dips. There is
probably a repetition of beds on Williams creek, such as is indicated on that
part of the general section corresponding to it. . . In that part of the
section corresponding to the crest of the Goose Creek mountains, it will be
better in accordance with the facts to conclude that some beds have been
inverted, than it would to assume a thickness of 30,000 feet. The total
thickness of the schists (Cariboo series) is probably as has been indicated
on the section, from 5,000 to 8,000 feet.”’

Bowman’s conclusions with regard to the thickness of the Cariboo
series agree in general with those based on the present investigation: but
the two methods of arriving at the same result were different. Bowman
apparently failed to recognize the difference between cleavage and bedding
planes in the schists and slates, and assumed, for instance, that a thick

10p. cit., pt. C, p. 24.