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ORIGIN OF PHYSICAL FEATURES

The mountains and valleys of Portland Canal area are closely related
to the hardness and structure of the rocks. The area in general is charac-
terized by high, jagged mountains and is in marked contrast with the sub-
dued mountains to the east. This difference is due in part at least to the
fact that the rocks of the area are harder than those of the adjacent part
of the interior of British Columbia. The main valleys and mountain
ridges are parallel to the strike of the rocks, and there can be little doubt
that the structure controlled the location and development of these
features. The higher mountains in the area consist of rocks relatively
resistant to erosion.

Detailed examination of the area suggests strongly that the location
of the main valleys and inter-valley ridges was controlled by the bedrock
structure and that the main features were fixed prior to the Pleistocene
epoch. The effect of the Pleistocene has only been to greatly modify the
shapes of the pre-existing land forms, to disorganize the drainage to some
extent, and to develop many minor features, as for example glacial cirques.
Erosion since the Pleistocene has formed many or all of the canyons of
the area.

A plateau surface 2,000 feet high extends from Alice Arm district
south to Nass river. The surface appears to rise northward and in Alice
Arm district to be represented by isolated, flat or gently sloping surfaces
from 3,000 tc 4,000 feet high. This plateau is probably an extension into
the Coast Range mountains of an old erosion surface found over a large
part of the interior of British Columbia. The plateau and the Coast
Range mountains probably at one time merged into one another, but very
active glacial erosion in the Coast Range mountains has destroyed most
or all of the plateau surface there, and has given the coast section a very
youthful appearance in contrast with that of the interior.

Kinskuch lake, in the northeastern part of Alice Arm district, appar-
ently occupies an ice-scoured basin. Upper Illiance river follows the strike
of soft, sheared rocks, and the westerly part of its course is along a contact
between volcanic rocks and sediments. A waterfall, 150 feet high, on the
river, is caused by a wide diorite dyke that acted as a resistant dam. The
eanyons on Dak river occur where the stream crosses igneous rocks and
the broader parts of the valley are cut through softer sediments. The
tributaries of Dak river are very deeply incised, apparently because they
are located in bands of sediments whereas the intervalley ridges consist
of harder igneous rocks.

The two upper canyons on Kitsault river are cut in hard, igneous
rocks, but the broad, open parts of the valley are in sediments. The lowest
canyon is in sediments intruded by several large dykes and the assemblage
is apparently more resistant than the average sedimentary rock. The
valleys of most of the tributaries of Kitsault river are in sediments in
their upper parts, but in igneous rocks near the main stream. The upper
parts of these valleys are broad and the stream gradient is gentle, whereas
the lower parts are in general canyons and the grade is steep. The hard-
ness of the rocks has had a great deal to do with the shapes of the tributary
valleys, but their hanging nature has resulted mainly from greater deep-