General Geology

thickness for the two subdivisions of at least 1,500 feet. In Whitesail Lake
map-area the discontinuous and unstratified nature of the outcrops makes it
difficult to attain any accurate figure for the thickness of the group. However,
the few attitudes observed in the area of these rocks near the foot of White-
sail Lake indicate a thickness of about 3,000 feet.

Structural Relations

Rocks of the Ootsa Lake group have been moderately disturbed, with
dips up to 55 degrees, although dips of 35 to 40 degrees are most common.
The rocks of the group near the mouth of Whitesail Lake are folded into a
shallow open syncline plunging to the northwest. Near the head of Ootsa Lake
available attitudes indicate a sharp anticlinal structure the axis of which strikes
west. Near Streatham the group is faulted by a northwest-trending fault, which
has caused shearing and slickensiding in the rhyolites exposed along the shore
of the lake.

The relationship of this group of rocks to those of the Hazelton group is
one of erosional unconformity as evidenced by the basal conglomerate on
Whitesail Lake. Granitic intrusions were not found in the group, nor does the
adjacent Quanchus batholith appear to have intruded or altered the rocks. No
definite contact between rocks of the group and the Quanchus batholith was
seen, though much time was spent searching for one.

Near the head of Ootsa Lake rocks of the group are very close to the
batholith but show no sign of metamorphism. It is, however, possible that the
contact there is a faulted one.

The two small islands at the head of Ootsa Lake are cut by black basalt
dykes which strike north 45 degrees west and dip 50 degrees to the northeast.

At several localities in the map-area the acid flows of this group are
overlain by flat-lying basalts of post-Oligocene age.

Age

No fossils were found in rocks of this group within the map-area but
relationships with older and younger rocks indicate a period of deposition
extending from the late Cretaceous to Oligocene. East of the map-area, at
Chief Louis Bay on Ootsa Lake, H. W. Tipper found both fossil leaves and
freshwater pelecypods and gastropods in sandstone and conglomerate beds

near the base of the group. .