of transition slopes.]

Gentle transition slopes or terrace lands facilitate almost everywhere
access to the lowest, most habitable and therefore, from the human
standpoint, most important section of mountains. They combine the ease
of intercourse characteristic of plains with many advantages of the
mountains, and especially in warm climates they unite in a narrow zone
both tropical and temperate vegetation. The human value of these
transition slopes holds equally of single hills, massive mountain
systems, and continental reliefs. The earth as a whole owes much of its
habitability to these gently graded slopes. Continents and countries in
which they are meagerly developed suffer from difficulty of intercourse,
retarded development and poverty of the choicest habitable areas. This
is one disadvantage of South Africa, emphasized farther by a poor
coastline. The Pacific face of Australia would gain vastly in historical
importance, if the drop from the highlands to the ocean were stretched
out into a broad slope, like that which links our Atlantic coastal plain
with the Appalachian highlands. There each river valley shows three
characteristic anthropo-geographical sub-divisions--the active seaports
and tide-water tillage of its lower course, the contrasted agriculture
of its hilly course, the upland farms, waterpower industries and mines
of its headstream valleys, each landscape giving its population
distinctive characteristics. The same natural features, with the same
effect upon human activities and population, appear in the long seaward
slopes of France, Germany and northern Italy.

[Sidenote: Piedmont belts as boundary zones.]

At the base of the mountains themselves, where the bold relief begins,
is always a piedmont zone of hilly surface but gentler grade, at whose
inner or upland edge every phase of the historical movement receives a
marked check. Here is a typical geographical boundary, physical and
human. It shifts slightly in different periods, according to the growing
density of population in the plains below and improved technique in
industry and road-making. It is often both an ethnic and cultural
boundary, because at the rim of the mountains the geologic and economic
character of the country changes.[1189] The expanding peoples of the plains
spread over the piedmont so far as it offers familiar and comparatively
favorable geographic conditions, scatter their settlements along the
base of the mountains, and h