77

tufaceous matrix. A large exposure of brillant red, soft, ar-
gillaceous sediments was seen several hundred feet below this
conglomerate. These beds are at least 100 feet thick, and
may be much thicker. The lower 40 feet includes some sills or
flows.

Some of the hills east of Otard bay and Port Louis on the
west coast are formed of bright red, bedded rocks, perhaps
sedimentary and similar to those just described.

These ferruginous rocks, occurring in a great volcanic
series, recall the deposition of hematite mud at the present day
in the Hawaiian islands,' another region of basaltic rocks, and
may be worth while prospecting for beds of sedimentary iron
ore.

Structure.—Internal. The Masset formation is formed
of bedded flows and agglomerates usually not exceeding 100
feet in thickness, both of which may be considered as thin and
relatively extensive lenses. This bedded nature of the forma-
tion is well seen in the Slatechuck range and at Lawn hill and
in fact in every exposure of the volcanics except those of very
small size. Many of the flows show well marked columnar
jointing. This jointing has been noted on Mount Etheline
and in a high degree of perfection on the west coast (Plate XIIIB).
Flow structure, so beautifully illustrated in thin section, is
well brought out by weathering in several localities, notably
at Lawn Hill beach.

Chalcedony and calcite veins intersect the rocks at Lawn
hill and Tian point, on the east and west coasts respectively,
at both localities carrying tar.

Structure —External. The actual contact of the Masset
volcanics with the underlying Cretaceous rocks was observed
at two localities on the southeast slope of Slatechuck mountain.
The contact is very sharp; the basalt is chilled for several inches
above its lower surface, and exhibits a distinct columnar and rude
platy jointing, the former perpendicular to this surface, and the
latter parallel to it. This lower surface is generally smooth,
but in detail somewhat mammillary, with projections reaching

1 Lindgren, W., ‘Mineral deposits,’’ McGraw-Hill Book Co., New York, N.Y., p. 200.