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underlying or overlying—he is dealing with is of the utmost
value. At least one case is known where several hundred feet
of useless drilling was done in the Yakoun volcanics, on the mis-
taken assumption that they were the overlying rocks.

This mistake may in part have arisen because the outcrops
occurred on a hill-side, above outcrops of the Haida formation,
which were not recognized as basal. The determination of the
fact that the coal measures were laid down on an uneven surface
is thus seen to have a direct economic bearing. Erosion has in
some degree bared the pre-Cretaceous topography, exposing the
hills against which the sediments of the Queen Charlotte series
were accumulated. It very often happens that the stratigraphic-
ally underlying Yakoun volcanics are, topographically,
above the stratigraphically overlying coal measures, owing
to normal processes of erosion having exposed the ancient topo-
graphy. It is essential to intelligent prospecting that these
peculiar structural relations be borne in mind, and it is largely
on account of them that the prospector and geologist must fall
back on petrological criteria for distinguishing which formation
of volcanics he has encountered.

Fortunately there are distinct megascopic differences, and
only occasionally need there be any uncertainty as to the identity
of the formation in the field. In these cases of doubt the power-
ful aid of the microscope may be invoked, for the microscopic
characteristics of the two series of rocks are even more distinctive
than the megascopic.

For convenience in reference the two formations are con-
trasted in detail under the same headings.

Yakoun Formation. | Masset Formation.

Age.
Middle Jurassic Pliocene (?)
Stratigraphic Position.

Unconformably overlying the coal-
bearing Queen Charlotte series.

Unconformably underlying the coal-
bearing Queen Charlotte series.