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on Buffalo river, and on the north shore at Slave point and along the lake shore
between House and Moraine points. _ :

“This formation is composed of thin-bedded, medium-grained, dark grey,
and slightly bituminous limestones and has an estimated thickness of about
160 feet.”

The middle Devonian limestone series is represented by a dolomitie lime-
stone in the upper part of the Clearwater section and by an outcrop of limestone
at the mouth of Mikkwa river below the chutes on the Peace. Another horizon
of this series outcrops opposite La Butte on Slave river.

The finest exposures of the middle Devonian limestones occur, however, in
the mountains which for 300 miles border one or both sides of Mackenzie river
between the mouth of North Nahanni and Carcajou rivers. These beds form the
sides of the three sharply folded anticlinal mountain ridges which trend east
and west in the vicinity of the mouth of Carcajou river. The higher slopes of
the Bear Mountain range, which extends along the eastern side of the Mackenzie
from the mouth of Great Bear river to the vicinity of Careajou mountain, consist
of middle Devonian limestone, which dipping towards the southwest, passes suc-
cessively under the upper Devonian and Cretaceous shales. These southwesterly
dipping limestones and the beds which follow them, together with the rocks in the
first range of the Mackenzie mountains southwest of Careajou river, may be
found to form the sides of a great synclinal trough some 30 miles in width. In
Bear mountain the middle Devonian limestones reach the river bank about 3
miles below Norman. Most of the southern end of this mountain consists of
Silurian sediments.

South of Norman for some 60 miles the middle Devonian limestones form
the slopes of mountains which are generally separated from the Mackenzie by a
plain floored with Cretaceous shales several miles in width. In Rock-by-the-
river-side opposite Wrigley the middle Devonian limestones again appear in
the bank of the Mackenzie. The western slopes of this mountain, Rocky island
immediately above Wrigley, and the adjacent eastern bank of the river consist
of middle Devonian limestones dipping at high angles. The end of the moun-
tain, which faces the river, shows a closely folded anticline, the northwest side
of which consists of Devonian limestones dipping at an angle of about 75 degrees.
‘The core of this anticline is a magnesian limestone which is believed to be of
Silurian age.

The western slopes of the mountain range which lies about 18 miles east of
Wrigley and extends south to Willow Lake river, consist in large part of middle
Devonian limestones. Silurian beds are known to form the top and eastern
face of this range east of Wrigley. The long east-facing scarp which extends
northward from North Nahanni river near the Great Bend of the Mackenzie is.
capped by middle Devonian limestone. The 2,000 feet or more of nearly barren
magnesian limestone below it appear to be of Silurian age. The Devonian
limestone on the summit of Lone mountain on the south side of the Nahanni
at the Great Bend has a thickness of about 220 feet. This limestone also caps
the great scarp which touches Liard river at the mouth of South Nahanni river.

The most northerly known occurrence of these limestones in the Mackenzie
basin is in a cliff exceeding 100 feet in height on Gull lake east of the Mackenzie
delta Gull lake is probably Campbell lake, or one of the small lakes near it
between the delta and the most southerly of the Eskimo lakes.

1 Kindle, E. M., Am. Jour. Sc., vol. 42, p. 246, 1916.