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The Central Plateau province is underlain largely by basins
of relatively soft, Cretaceous sediments, separated by higher
ridges of pre-Cretaceous metamorphic and volcanic rocks. The
name plateau is given to the division because this part of the
island—the south-central—is characterized by a number of
hills, from 1,000 to 1,500 feet high, with a general accordance of
summit level, some of them flat-topped ridges, others plateau-
like, as i!lustrated in Plates IV and V. These higher elevations
are composed of the pre-Cretaceous rocks, or, rarely, of the more
resistant Cretaceous beds, and are separated by wide valleys
carved from the more easily denuded Cretaceous sediments.
It thus happens that many of the topographic depressions are
underlain by geologic basins. Skidegate inlet and the Honna
valley, in part, are instances of such depressions. From the
middle of township 8, the boundary of the Queen Charlotte
range passes northward through the entrance of Juskatla inlet,
crosses Masset inlet, follows up the Ain river, and, curving west-
ward around the head of Naden harbour, reaches the west coast
about 6 miles north of Frederick island. It is thus apparent
that the Queen Charlotte range does not reach the north coast
of Graham island.

This northern portion, west of Naden harbour, is termed the
Northern lowland, and is chiefly underlain by Tertiary basalt
and pyroclastic rocks, with pre-Cretaceous rocks occurring in
the northwestern corner. The Northern lowland (Plate VIII A)
has no elevations exceeding 500 feet, although the surface
is hilly and irregular.

The Northeastern lowland is a striking feature of Graham
island, comprising the district east and northeast of the prov-
inces just described. It is underlain largely by partially or
wholly unconsolidated sediments of Tertiary age, with some
areas of younger Tertiary volcanics, forming flat-topped hills.
Apart from these the district is a low, gently undulating plain,
densely forested, except where muskegs, which are of consider-
able total area, occur (Plate VIIA).