61

various long and nearly parallel bays into which this portion of the lake is
divided. These rocks consist partly of unaltered limestones varying in colour
from very light- to dark-grey, drab, and red, sometimes passing into shales, and
partly of sandstones, mostly red, coarse conglomerates, and red shales, together
with thick sheets or overflows of greenstone, generally capping the other strata
and presenting long cliffs made up of perpendicular columns or “ palisades”
overlooking the different bays. We could not ascertain whether all these green-
stone cappings belonged to a single extensive overflow or not. Large exposures
of greenstone also occur near the level of the lake, which may not form part of
any general overflow. A few wide,greenstone dykes were seen cutting the nearly
horizontal Animikie strata beneath the crowning overflow.”

In the narrows, southeast of Big Caribou island and on the Rentlecuiés of land
sepurating McLeod bay from the east bay, there are exposures of “ massive
light-grey, blue, or dove-coloured limestones which weather to various shades
of yellow and brown, hard reddish sandstones or quartzites and fine conglomerates,
and red and grey ‘lumpy’ jasper or chert rock. At the east bay, black shale
occurs in the vicinity of the massive limestone.”

Sedimentary rocks of various kinds, associated with basic igneous intrusives,
are exposed at the eastern end of Great Bear lake and extend eastward beyond
Coppermine river and northward to the Arctic ocean.

At Limestone point, on the north shore of Dease bay, 30 miles west of Fort.
Confidence, there is an exposure of “purplish dolomite which changes to a
ferruginous slate. Above this comes. grey, semi-crystalline dolomite, associated
with light-grey quartzite.” Limestones and slates are exposed at points along
the shore to the east of this. Exposures of limestone, quartzite, sandstone, and
basic igneous rocks occur on the rough, rocky south shore of Dease bay as far

west as Narrakazoe islands. On these islands greenstone is exposed. West of |

this the south shore of Dease bay is low, as is also the north shore of McTavish
bay for 50 miles east of cape McDonnel. Farther east the shore of McTavish
bay is rocky, and greenstone intrusions are found cutting horizontal sediments.?
“The eastern part of McTavish bay is composed of a series of basic rocks, or
greenstones, that seem to overlie the Laurentian granites, of which, however,
exposures are seen at several places. The southern part of McTavish bay and
the islands there, are mostly of granite, though greenstone dykes are common.”
On Dease river bright red quartzite, and drab and red magnesian limestones
occur, and at its mouth exposures of diabase and diorite are seen.

On Coppermine river, which lies east of Great Bear lake outside the basin
of the Mackenzie, a number of basaltic flows, the upper parts of which are
amygdaloidal, are found interbedded with conglomerate, sandstone, and shale.
These rocks are of wide distribution, being found on Coppermine river, on the
coast and islands to the north, and on Bathurst inlet. Their chief interest lies
in the fact that they carry native copper.*

Paleozoic (not subdivided)

The Mackenzie basin includes extensive areas in which the sedimentary
series has not been sufficiently studied to differentiate the subdivisions of the
paleozoic rocks. This is true of most of the region between Great Bear and

1 Bell, J. M., Geol. Surv., Can., Ann, Rept., vol. XII, p. 26 C.

2Dougias, James, “The copper-bearing traps of the Coppermine river,’‘ Can. Min.
Inst., Trans., vol, XVI, pp. 83-1011.

O'Neill, J. J., Geol. Surv., ‘Can., Sum. Rept., 1916.

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