INTRODUCTION
NORTH AMERICAN GEOLOGY
Whereas the
geological growth of Europe presents the record of an archipelago of
forming points, with continental or semi-continental areas to which
they were referable, slowly consolidating into a continuous surface,
the corresponding geological development of North America presents
contrastedly a picture of consecutive additions to a nucleal and
primary framework. Its geological history in outline is more simple.
The preponderating initial land surfaces were, at the north, with
longitudinal alignments along the eastern and western edges of the
continental uplift, with a few interior centers of elevation (Missouri,
Minnesota, Wisconsin, Texas, Dakota) ; and the sequence of the
appearance of land surfaces was from the north southward, and laterally
east and west on the borders of the two long descending ridges defining
the sides of the continent, as against the submerged and cavernous
troughs of the Atlantic and Pacific oceans.
In
the geological history of Europe we are confronted with a series of
slowly filled-up basins converted into land surfaces. In America an
early architectonic outline of a primordial continent appears with two
limbs, stretching southward. These .enclose a broad and shallow basin
more open on the west, whose floor underwent secular changes of
elevation and depression. Generally these changes enlarged the land
surfaces, progressively through geological time, from north to south,
and inwardly on the edges of the two limbs, while on the extreme east
and west the continent also grew outward, in an encroachment on the
Atlantic and Pacific oceans. The
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