57

TABLE OF FORMATIONS—Concluded.

Unconformity.
MRSS Soe eet ee ee
Upper Devonian... . m0. c ee en deat eeeenens fs tech Shales and limestones.
WMiddila Devonian : Oo sot eee eae cece tet es Seale: Limestones with some
shales.
Palewozoic.........:
Unconformity.
Silurian. ...2. . Sirs See ris Se Se oe tea ; Rey ae Dolomites and. shales

with gypsum.

ee Ne ee eS eS

Unconformity.
ee ee
BatecPreGam Driates cs. soca oe ieekis Betelethees cape wie Se ne Sandstone, limestone,
and basic flows and
intrusives.
pe uh a te ee a ee
Unconformity.

sae a1 Ga ae a ae ae ee ae ea

Precambrian.....,.|Granites and gneiSSeS.....--...--. + -eee rset tr eee:

Inirusive Contac t.

he eS SS

Early Precambrian.......... 06.2 e cece eee terete ee: Schists, slates, lime-
stones, and. quartz
ites.

4
DESCRIPTION OF FORMATIONS

Precambrian

The distribution of the Precambrian rocks of the Mackenzie basin -coincides
with the physiographic province known as the Laurentian plateau, which occupies
a strip along the eastern border of the basin about 800 miles in length and
ranging from 80 to 280 miles in width. On the east, the Precambrian rocks
extend far beyond the boundaries of the region over to Hudson bay, but on the
west they pass under a cover of later stratified rocks. The contact with these
younger rocks runs from Methy portage to the west end of Athabaska lake, thence
- down the valley of Slave river to Great Slave lake, and from the north arm oi
that lake north-northwesterly to McTavish bay on Great ‘Bear lake. North of
Great Bear lake the contact has not been defined, but it probably soon passes
northward outside the watershed of Mackenzie river, reaching the Arctic coast
at Darnley bay.

: The Precambrian rocks of this region have not been subdivided in such great
detail as they have been in the Lake Superior region or in northern Ontario, and
-only three different subdivisions have been recognized and mapped. More detailed
work will no doubt show the same complexity of formations as exists in other
regions where the Precambrian has been more carefully studied.

The oldest of the three groups of rocks into which the Precambrian has been
subdivided consists of highly metamorphosed schists, slates, limestones, quartz-
ites, and volcanic rocks, occurring in isolated areas as erosion remnants, This
group includes formations that have been uncertainly correlated with the Kee-
watin, Huronian, or Grenville of other regions.

ice nea

SS