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).

[Illustration:  Fig. 20.—­Diagrammatic section of the Laurentian Rocks in Lower Canada. a Lower Laurentian; b Upper Laurentian, resting unconformably upon the lower series; c Cambrian strata (Potsdam Sandstone), resting unconformably on the Upper Laurentian.]

The Lower Laurentian series attains the enormous thickness of over 20,000 feet, and is composed mainly of great beds of gneiss, altered sandstones (quartzites), mica-schist, hornblende-schist, magnetic iron-ore, and haematite, together with masses of limestone.  The limestones are especially interesting, and have an extraordinary development—­three principal beds being known, of which one is not less than 1500 feet thick; the collective thickness of the whole being about 3500 feet.

The Upper Laurentian series, as before said, reposes unconformably upon the Lower Laurentian, and attains a thickness of at least 10,000 feet.  Like the preceding, it is wholly metamorphic, and is composed partly of masses of gneiss and quartzite; but it is especially distinguished by the possession of great beds of felspathic rock, consisting principally of “Labrador felspar.”