144 PHYSIOGRAPHY, GEOLOGY AND MINERAL RESOURCES

Plateau, and often admit throughout their entire length of the
entrance of the largest ocean-going vessels. The deeper channels
are generally the continuation of the leading rivers, which suddenly
change in character as they enter the Coastal Plain with great loss in
the velocity of their currents. All of the large streams and many
of the smaller ones as they cross the western margin of the Coastal
Plain are characterized by a marked decrease in the velocity of their
currents and at times by falls or rapids, the name " fall-line " being-
given to this boundary on that account. The inland border of the
Coastal Plain thus marks the head of navigation and has likewise
conditioned from the earliest times the leading highways of trade
which connect the north and south. Along this line have grown up
the larger cities of the Atlantic seaboard, Trenton, Philadelphia,
Baltimore, Washington, Richmond, Petersburg, Columbia, Augusta,
and other less populous towns.

The Piedmont Plateau, which borders the Coastal Plain upon the
west and extends thence to the foot of the Appalachian Mountains,
is less clearly defined in the northern portion of the country than
along the middle and southern Atlantic slope. It broadens from New
York southward, reaching its greatest width of three hundred miles
in North Carolina. The Piedmont Plateau is a region of somewhat
greater elevation than the Coastal Plain which borders it upon the
east, but stands in marked contrast to the high ranges of the Appa-
lachian Region upon the west. It is characterized by a broken, hilly
country with undulating surface^ but with few mountains of con-
spicuous altitude or great extent. The region is crossed by numerous
rivers which have their rise in the high mountains to the west, while
many smaller streams and tributaries have their sources within the
area. The streams flow with rapid currents and the country is every-
where well drained as compared with the low lands of the east.

The Appalachian Region is an area of high land which extends
almost continuously from Cape Gaspe in Canada southward to Ala-
bama, a distance of 1300 miles, and throughout most of that distance
forms the divide between the streams which flow directly to the east
across the Piedmont Plateau and the Coastal Plain into the Atlantic