railroad, excluded all but strong-limbed and strong-hearted pioneers
from the fertile valleys of California and Oregon, just as it excludes
coal and iron even from the Colorado mines, and checks the free
movement of laborers to the fields and factories of California, thereby
tightening the grip of the labor unions upon Pacific coast industries.

[Sidenote: Persistent effect of nature-made highways.]

As the surface of the earth presents obstacles, so it offers channels
for the easy movement of humanity, grooves whose direction determines
the destination of aimless, unplanned migrations, and whose termini
become, therefore, regions of historical importance. Along these
nature-made highways history repeats itself. The maritime plain of
Palestine has been an established route of commerce and war from the
time of Sennacherib to Napoleon.[1] The Danube Valley has admitted to
central Europe a long list of barbarian invaders, covering the period
from Attila the Hun to the Turkish besiegers of Vienna in 1683. The
history of the Danube Valley has been one of warring throngs, of
shifting political frontiers, and unassimilated races; but as the river
is a great natural highway, every neighboring state wants to front upon
it and strives to secure it as a boundary.

The movements of peoples constantly recur to these old grooves. The
unmarked path of the voyageur's canoe, bringing out pelts from Lake
Superior to the fur market at Montreal, is followed to-day by whaleback
steamers with their cargoes of Manitoba wheat. To-day the Mohawk
depression through the northern Appalachians diverts some of Canada's
trade from the Great Lakes to the Hudson, just as in the seventeenth
century it enabled the Dutch at New Amsterdam and later the English at
Albany to tap the fur trade of Canada's frozen forests. Formerly a line