To obtain, however, a still more correct notion of the appearance of the
continent, we must take another glance over it. We shall discover, to
the north, and throughout the eastern portion where civilised man has
not been at work dealing away the trees, a densely-wooded region.
Proceeding westward, as the valley of the Mississippi is approached the
underwood disappears, and oak openings predominate. These Oak Openings,
as they are called, are groves of oak and other forest-trees which are
not connected, but are scattered over the surface at a considerable
distance from one another, without any low shrub or underbrush between
them.