d that the appearance
of the lower forms of life has in the main preceded that of the
higher forms in point of time.

PART II

HISTORICAL PALAEONTOLOGY

CHAPTER VII.

THE LAURENTIAN AND HURONIAN PERIODS.

The _Laurentian Rocks_ constitute the base of the entire stratified
series, and are, therefore, the oldest sediments of which we have
as yet any knowledge. They are more largely and more typically
developed in North America, and especially in Canada, than in
any known part of the world, and they derive their title from
the range of hills which the old French geographers named the
"Laurentides." These hills are composed of Laurentian Rocks, and
form the watershed between the valley of the St Lawrence river
on the one hand, and the great plains which stretch northwards
to Hudson Bay on the other hand. The main area of these ancient
deposits forms a great belt of rugged and undulating country,
which extends from Labrador westwards to Lake Superior, and then
bends northwards towards the Arctic Sea. Throughout this extensive
area the Laurentian Rocks for the most part present themselves
in the form of low, rounded, ice-worn hills, which, if generally
wanting in actual sublimity, have a certain geological grandeur
from the fact that they "have endured the battles and the storms
of time longer than any other mountains" (Dawson). In some places,
however, the Laurentian Rocks produce scenery of the most magnificent
character, as in the great gorge cut through them by the river
Saguenay, where they rise at times into vertical precipices 1500
feet in height. In the famous group of the Adirondack mountains,
also, in the state of New York, they form elevations no less than
6000 feet above the level of the sea. As a general rule, the
character of the Laurentian region is that of a rugged, rocky,
rolling country, often densely timbered, but rarely well fitted
for agriculture, and chiefly attractive to the hunter and the
miner.

As regards its mineral characters, the Laurentian series is composed
throughout of metamorphic and highly crystalline rocks, which
are in a high degree crumpled, folded, and faulted. By the late
Sir William Logan the entire series was divided into two great
groups, the _Lower Laurentian_ and the _Upper Laurentian_, of
which the latter rests unconformably upon the truncated edges
of the former, and is in turn unconformably overlaid by strata
of Huronian and Cambrian age (fig. 20).

[Illus