Hence rivers in the Appalachians are not navigable; it is only farther down-stream, where the rivers have been converted into estuaries and bayssuch as Chesapeake and Delaware baysby a slight depression of the coastal plain belt, that they serve the purposes of navigation.
The middle section of the Appalachians is further distinguished from the north-eastern and south-western sections by the arrangeDrain age.
Evi-Jently, therefore, the Appalachians as we now see them are not the still surviving remnants of the mountains of late Palaeozoic deformation; they owe their present height chiefly to the Tertiary upwaroing and uoliftinr.
The rivers that drain the Atlantic slope of the Appalachians are comparatively short; those that drain the Pacific slope include only two, the Columbia and the Colorado, which rise far inland, near the easternmost members of the Cordilleran system, and flow through plateaus and intermont basins to the ocean.
There is one feature of the Appalachians that has greater continuity than any other; this is the Great Valley.
For a century the Appalachians were a barrier to the westward expansion of the English colonies; the continuity of the system, the bewildering multiplicity of its succeeding ridges, the tortuous courses and roughness of its transverse passes, a heavy forest and dense undergrowth all conspired to hold the settlers on the seaward-sloping plateaus and coastal plains.
The state is divided into two distinct physiographic provinces; the Alleghany Plateau on the west, comprising perhaps two-thirds of the area of the state, and forming a part of the great Appalachian Plateau Province which extends from New York to Alabama; and the Newer Appalachians or Great Valley Region on the east, being a part of the large province of the same name which extends from Canada to Central Alabama.
The invasion was wonderfully accelerated through the I9th century, when the vast area of the treeless prairies beyond the Appalachians was offered to the settler, and when steam transportation on sea and land replaced sailing vessels and wagons.
The upper Mississippi and some of the Ohio basin is the prairie region, with trees originally only along the watercourses; the uplands towards the Appalachians were included in the great eastern forested area; the western part of the plains has so dry a climate that its herbage is scanty, and in the south it is barren.
New York, where the Appalachians enter the state, the plateau becomes much higher than in the W., reaching its culmination in the Catskills.