to the Old is the direct similarity of North and South America.
In physical form the two continents are astonishingly alike. Not
only does each have the typical triangular form which would
naturally arise from tetrahedral shrinking of the globe, but
there are four other cardinal points of resemblance. First, in
the northeast each possesses an area of extremely ancient rocks,
the Laurentian highlands of Quebec and Labrador in North America
and the highlands of Guiana in South America. Second, in the
southeast lie highlands of old but not the most ancient rocks
stretching from northeast to southwest in the Appalachian region
of North America, and in the Brazilian mountains of the southern
continent. Third, along the western side of each continent recent
crustal movements supplemented by volcanic action on a
magnificent scale have given rise to a complex series of younger
mountains, the two great cordilleras. Finally, the spaces between
the three mountain masses are occupied by a series of vast
confluent plains which in each case extend from the northern
ocean to the southern and bend around the southeastern highlands.
These plains are the newest part of America, for many of them
have emerged from the sea only in recent geological times. Taken
as a whole the resemblance between the two continents is
striking.

If these four physiographic provinces of North and South America
lay in similar latitudes in the respective continents we might
expect each pair to have a closely similar effect on life. In
fauna, flora, and even in human history they would present broad
and important resemblances. As a matter of fact, however, they
are as different as can well be imagined. Where North America, is
bathed by icy waters full of seals and floating ice South America