16

The dykes of this zone may be the top of an elongated stock. It is
possible that a zone of weakness was developed parallel with the border
of the Coast Range batholith during its intrusion, and that magma from
the batholith riddled this zone with dykes. If this idea is correct the
dykes will coalesce with the batholith in depth.

Large dykes and sills of granodiorite intrude the older rocks near the
contact of the Coast Range batholith. These dykes and sills are off-
shoots of the batholith. They are very similar to the batholith in mineral
composition, but are usually somewhat different in texture, often exhibit-
ing porphyritic crystals. On mount Dolly a dyke of this type in voleanic
rocks can be traced into the batholith where a short distance from the
contact it merges with the batholithic rock.

Narrow, dark-coloured lamprophyre dykes are fairly common and
appear to be the youngest rocks in the area. Some are older and some
younger than the ore deposits with which they are occasionally associated.

PLEISTOCENE AND RECENT DEPOSITS

Glacial drift is present along the sides and lower limits of glaciers.
Older boulder clay is plentiful along Bitter creek and probably also along
the lower part of Bear river. Glacial erratics occur up to elevations 6,000
feet above sea-level, but are not numerous.

Recent silts, gravels, and blue clays containing marine shells were
noted by McConnell! on the lower part of Bitter Creck valley, and along
Bear river above Bitter creek for some distance past Bear lake. MeCon-
nell estimated the maximum thickness as 155 feet. Similar clays are pres-
ent on Marmot river. The clays are 350 to 450 fect above sea-level, and
the silts extend about 100 feet higher.

Bear River valley from American creek to its mouth is floored with
gravels and sands deposited by the present stream. During times of high
water, the stream commonly alters its course and, sweeping against the
bands, undercuts them and in this way widens the treeless part of the val-
ley bottom. A flat area several square miles in extent has been built up
at the mouth of Bear river; on it is the town of Stewart. The flat is being
rapidly extended seaward by stream-carried sediment. Data obtained by
the Department of Public Works of Canada show that on the west side of
Portland canal the low-water mark on the delta advanced 540 feet between
1909 and 1927. The rate in this place is 30 feet a year. It may be some-
what faster in the centre of Portland canal.

FAULTS

Faults are probably numerous in the area. Definite breaks were seen
in many places and were topographically expressed, but it was difficult or
impossible to determine the direction and extent of the throw or the offset.
Only where faults cut across strata with individual characteristics could
anything definite be learned about the extent of the movement along the
fault plane.

*McConnell, R. G.: Geol. Surv., Canada, Mem. 32, p. 22 (1913).