Puke Rob ee 
CHA PT ERS NATE 
THE LAURENTIAN AND HURONIAN PERIODS. 
THE Laurentian Rocks constitute the base of the entire strati- 
fied 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 geo- 
graphers named the “Laurentides.” These hills are com- 
posed 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 “Shave 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 ver- 
tical 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 
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