nce. When the crust of
the earth was so thin that the heated masses within easily broke through
it, they were not thrown to so great a height, and formed comparatively
low elevations, such as the Canadian hills or the mountains of Bretagne
and Wales. But in later times, when young, vigorous giants, such as the
Alps, the Himalayas, or, later still, the Rocky Mountains, forced their
way out from their fiery prison-house, the crust of the earth was
much thicker, and fearful indeed must have been the convulsions which
attended their exit.

The Laurentian Hills form, then, a granite range, stretching from
Eastern Canada to the Upper Mississippi, and immediately along its base
are gathered the Azoic deposits, the first stratified beds, in which the
absence of life need not surprise us, since they were formed beneath a
heated ocean. As well might we expect to find the remains of fish or
shells or crabs at the bottom of geysers or of boiling springs, as on
those early shores bathed by an ocean of which the heat must have been
so intense. Although, from the condition in which we find it, this
first granite range has evidently never been disturbed by any violent
convulsion since its first upheaval, yet there has been a gradual
rising of that part of the continent, for the Azoic beds do not lie
horizontally along the base of the Laurentian Hills in the position in
which they must originally have been deposited, but are lifted and rest
against their slopes. They have been more or less dislocated in this
process, and are greatly metamorphized by the intense heat to which they
must have been exposed. Indeed, all the oldest stratified rocks have
been baked by the prolonged action of heat.

It may be asked how the materials for those first stratified deposits
were provided. In later times, when an abundant and various soil covered
the earth, when every river brought down to the ocean, not only its
yearly tribute of mud or clay or lime, but the _debris_ of animals and
plants that lived and died in its waters or along its banks, when every
lake and pond deposited at its bottom in successive layers the lighter
or heavier materials floating in its waters and settling gradually
beneath them, the process by which stratified materials are collected
and gradually harden into rock is more easily understood. But when the
solid surface of the earth was only just beginning to form, it would
seem that the floating matter in the sea can hardly have