27

North of Rennell sound the Queen Charlotte range is almost
wholly underlain by Tertiary volcanic rocks and many cuesta-
shaped peaks are formed. The mountains are notso rugged as those
farther south, and a large number of the mountain tops are bare.
Many of these bare summits are rounded as if by glacial action
(Plate IIIB); but on examination it is seen that another process
#5 the cause of their subdued character. Everywhere above tree
line, which varies in elevation although usually over 1,300 feet,
the summits are mantled with an accumulation of sharply angular
fragments of the basalt and hard tuffs which form the hills.
These fragments are from } inch to 6 inches in size, but average
about 3 inches, and in shape remind one of the spalls of rock seen
in a stone cutter’s yard. The climatic conditions are such that
the mist-wreathed and rain-drenched hills at this elevation are
subjected to rapid and frequent alternations of freezing and
thawing, and it is well known that scarcely any weathering agent
is more destructive to rock surfaces. The effect of this action
is to rapidly disintegrate all exposed ledges, and to reduce them
to a condition where at the highest part the shattered bedrock
may be seen projecting from a blanket of debris. The little
hollows and irregularities in the surface of the ridges become
filled with accumulations of these angular spalls of rock. The
slopes leading to the hollows present a curiously streaked ap-
pearance, due to the classifying action of moving water on the
loose mass of rock fragments. The effect of this process is to
smooth out the irregularities of the surface by breaking down
the projections and depositing the debris in the hollows. The
rounded contours of the crestlines and hill tops is the result.
The process is in effect a phase of what had been called equi-
planation! by Cairnes.

Northern Lowland.

About 6 miles north of Frederick island, the Queen Char-
lotte range, which to this point has fringed the west coast of
Graham island from Skidegate inlet, rather abruptly loses its
mountainous character, and is continued, if the term be per-

1Cairnes, D. D. Bull. Geol. Soc. America, Vol. 23, 1912, pp. 333-348.