Page 50 - Annuaire Statistique Québec - 1918

:3-GEOLOGICAl SKETCH OF THE PROVINCE OF QUEBEC (1)

The Province of Quebec is divided into three main geological
provinces, and it is remarkable how distinct they are from each other
and how little they overlap or encroach on one another. They are the
Laurentian Plateau region (93 p. c. of the total area of the Province),
the Appalachian and St. Lawrence Lowlands regions.
The Laurentian Plateau.
The Laurentian Plateau occupies that part of the Province of
Quebec whieh lies ta the north of a straight Ene j oining the cities of
Otta,va and Quebec, and to the north of the estuary of the St. Lawrence
River below the latter city. Tt ext~nds ta Hudson Bay and Hudson
Strait. .
Except for a few outliers of later rocks, the Laurentian Plateau is
altogether underlain by rocks older than those of the Cambrian period.
Collectively they are refel'l'ed to as Pre-Cambrian. Similar rocks are
found on the west side of Hudson Bay, and, in fact, the Pre-Cambrian
rocks of the Laurentian Plateau occupy nearly three-fifths of the whole
of Canada. Therefore, although the great majority of the rocks of
the Laurentian Plateau are igneous rocks, often granitic, but more
frequently gneissic in structure, there are throughout the Pre-Cambrian
region assemblages of rocks always highly altered, but which sometimes
can be recognized as having been of the nature of sediments, or of
volcanic rocks fonned on the surface.
The Appalachian Region.
The Appalachian Region of the Province of Quebec lies to the
south-el1st of a line running north-east from the foot of Lake Champlain
to the city of Quebec, and to the south of the estuary of the River
St. Lawrence below this city. It i8 a part of a mountainous belt, the
Appalachian Mountains system, in which the strata are highly folded
and faulted, and bearing Humerous evidence of igneous activity. This
system of mountains, ridges and folds, continues on in the same south-
western trend jnto the United-States, as far as Alabama. In the Prov-
ince of Quebec, the Appalachian region, therefore, comprises the
eastern part of the Eastern Townships, the regions of Beauce, Temis-
couata, lVIatapedia and nearly the whole Gaspé peninsula.
The lov'lest and highest rock formations found in the Province of
Quebec are both represented in the much disturbed Appalachian Region.
In the Eastern Townships and the Beauce district, Cambrian and Ordo-
vician strata occupY large arcas; in the Gaspé peninsula, the Silurian
is largely devc1oped, with smaller areas of Devonian and Devono-
Carboniferous. lVIoreover, the orogenic, or mountain building forces,
which, acting from the east, crumpled the strata into roughly parallel
ridges of folds, overthrusts and faults, and elongated bands, striking
north-el1st and south-west, have uplifted and exposed the crystalline

(1) Dy Theo. C. Denis. C. E., Sllperinlendenl of Mine', Quebec Dure"u of Mine•.