this the one place where the highly complex Appalachian system
can easily be crossed. If the Alleghany plateau joined the
Adirondacks, Philadelphia instead of New York would be the
greatest city of America. Where the plateau first rises on the
south side of the Mohawk, it attains heights of four thousand
feet in the Catskill Mountains. We think of the Catskills as
mountains, but their steep cliffs and table-topped heights show
that they are really the remnants of a plateau, the nearly
horizontal strata of which have not yet been worn away. Westward
from the Catskills the plateau continues through central New York
to western Pennsylvania. Those who have traveled on the
Pennsylvania Railroad may remember how the railroad climbs the
escarpment at Altoona. Farther east the train has passed
alternately through gorges cut in the parallel ridges and through
fertile open valleys forming the main floor of the inner valley.
Then it winds up the long ascent of the Alleghany front in a
splendid horseshoe curve. At the top, after a short tunnel, the
train emerges in a wholly different country. The valleys are
without order or system. They wind this way and that. The hills
are not long ridges but isolated bits left between the winding
valleys. Here and there beds of coal blacken the surface, for
here we are among the rocks from which the world's largest coal
supply is derived. Since the layers lie horizontally and have
never been compressed, the same material which in the inner
valley has been changed to hard, clean-burning anthracite here
remains soft and smoky.

In its southwestern continuation through West Virginia and
Kentucky to Tennessee the plateau maintains many of its
Pennsylvanian characteristics, but it now rises higher and