52

district; but the Graham Island seams differ from those at
Nanaimo in being irregular on account of differences in the
amount of material originally deposited, while the Nanaimo
seams were affected by movements in the rocks after they were
partially consolidated.

ORIGIN OF THE COAL.

The problem of the origin of the coal seams naturally is
divided into two parts: the question of the mode of accumula-
tion of the seams, and the question of the formation of the
different grades of coal. The first question is the more general
and, so far as the evidence goes, applies with equal force to the
different occurrences; but the origin of the different types of
coal, such as the bituminous of Camp Wilson, the coked coal
of Yakoun lake, or the anthracitic material at Cowgitz, is a
problem to be treated separately in each case.

In the discussion of the origin of the Queen Charlotte series
it was brought out that those sediments are supposed to have
been formed in estuarine basins bordered by land of at least
moderate relief. In order that vegetable strata might accumu-
late in these basins a number of conditions must be fulfilled.
It is evident from the character of the rocks associated with the
coal that they were laid down under uniform, quiet, shallow water
conditions; such conditions might obtain after an estuary or bay
was largely filled with detritus, and when the heavier seas and
stronger currents were prevented from disturbing the water by
seaward bars, shoaling water, vegetable growth, or all three.
It is almost axiomatic that the plants that formed what we know
as the coal seams of the present day, grew in fresh or at most
brackish water.! It is concluded, therefore, that on Graham
island, marshes, consequent on the filling of the basins by sedi-
ments, allowed vegetation to obtain a foothold along the shore,
and this fringe was rapidly pushed seaward over the muds of
the estuary. It is further generally conceded that plant growth
in former geological periods was on a vastly greater scale than

1 White, D. and Thiessen, R., ‘‘ The origin of coal,’’ U. S. Department of the Interior,
Bureau of Mines, Bull. 38, 1913, p. 61.