the Piedmont tableland, east and south of it, to heights far greater than the Alleghanies attain. Beginning prominently in South Mountain, in southern Pennsylvania, it stretches Southwestward in greater and greater heights, through Virginia and western North Carolina, where it divides, the northern branch continuing westward to Georgia as the Unaka, or Great Smoky Mountains. These form a broad mass of mountains on the border between North Carolina and Tennessee, containing peaks exceeding those of the White Mountains of New Hampshire, and consequently the highest east of the Rocky Mountains. The culminating group, reaching in Mount Mitchell 6710 feet, is known as the Black Mountains (q.v.), and contains many peaks above 6000 feet in height. The Unaka Mountains are characterized by the great sharp-ridged spurs which leave the main chain and preserve its-height for a distance of several miles; between these spurs are deep valleys only wide enough at the bottom for the creek-beds which are invariably found there. The altitudes of the extended valleys in this great highland region are from 2000 to 3000 feet. To the west of the steep-sided Unaka ridge lies a valley, about 50 or 60 miles wide, in Tennessee, which contains the Tennessee River and its tributaries, the Clinch, Holston, and French Broad.
Geology. The Appalachian Mountains are folded mountains; that is, they have been formed by plications or, folds of the rock layers that make up the crust of the earth in this region, and the particular type of plication is so well developed in this region that it has received the name of the “Appalachian type” of folding. The Blue Ridge, along the eastern side, consists of layers of crystalline rocks, the oldest known in the Appalachians, that have suffered so great an amount of metamorphism as to render the determination of their exact age a matter of considerable difficulty. They are grouped under the term “fundamental complex,” and it is certain that they are in large part pre-Cambrian; and some are even Archæan on the eastern edge of the Blue Ridge. On the western edge isolated masses of Cambrian rocks are found. All these rocks of the Blue Ridge have been much folded and compressed, so that the layers now stand almost on end and are even overturned. Great faults and overthrusts are common, and add to the difficulty of unraveling the structure of the district. In the Appalachian Valley the geological structure is also quite complex, though the strata are not so intensely metamorphosed. The rocks are limestones, shales, and sandstones, and they lie in closed folds that become more open toward the western side of the valley. These folds are peculiar in that their eastward slopes are always steeper than the westward. When the folds are overturned the inversion is toward the east; and overthrusts are also toward the east, and often of considerable extent. This valley is largely the result of the erosion of a great limestone formation, of Cambro-Silurian age, that extends its entire length. The Alleghany Mountains consist of rocks of Paleozoic age, Cambrian to Carboniferous, inclusive, that have been elevated into folded ridges and then eroded to their present topography. The softer beds have been worn into valleys, and the harder beds, having resisted erosion, have been left to form the ridges and benches. In this limestone also have been erod- ed the wonderful series of caves of the Shenandoah Valley and elsewhere, of which that at Luray, Va., is a striking example (see Caves). Anticlinal and synclinal folds alternate in diminishing intensity toward the west, where they disappear in the nearly horizontal beds of the Cumberland Plateau, which is made up of carboniferous rocks.
Drainage Development. The region now occupied by the Appalachian Mountains has been the scene of many physiographical changes too complex to explain here. At a comparatively recent time, however, the whole of the Appalachian system consisted of a great rounded plateau with an elevation of perhaps 4000 feet, the surface of which is called by geologists the Kittatinny Plain. Above this plain arose to a moderate height the now high mountains of western North Carolina. Along a central zone the land increased in altitude to a region in Virginia which thus became the watershed. The rain now did its work, and the great rivers—the New, the Roanoke, James, Potomac, and Susquehanna—cut out their paths through the then nearly level region, and a well-developed system of highlands and drainage was established. However, the subsequent elevation of land in this region by amounts ranging from 200 feet in the north to 1700 feet in Virginia, once more disturbed the adjustment of the water systems, and gave a new impetus to the work of the flowing waters.
While the Appalachian Mountains form the watershed between the Atlantic Slope and the Mississippi Valley, yet throughout there is no definite watershed line on one side of which the rivers flow to the west, and on the other toward the east. In the northern part the streams chiefly break through the mountains from the western side to the east. In the middle part, some escape toward the east and some toward the west; while at the south the eastern mountain range of the Blue Ridge forms the watershed. The water-courses appear to be independent of the direction of the mountain ranges, and instead of pursuing what appear to be the natural directions along the present great valleys, they flow across the ridges through deep gaps in them. This peculiar circumstance is due to the fact that these gaps were cut by the streams before the intervening ridges were upheaved.
The chief streams draining the eastern slope of the Appalachian into the Atlantic are the Hudson and its branches on the west, the Delaware, Schuylkill, Susquehanna, Potomac, and the James, which cut their way eastward through the mountain ranges; and the Rappahannock, Dan, Yadkin (Pedee), Catawba, Broad, Saluda (branches of the Santee), and the Savannah, which rise from the eastern slope of the Blue Ridge, whose western slopes drain into the Susquehanna, Shenandoah (Potomac), James or Tennessee. On the south are the Chattahoochee (head stream of the Apalachicola ) and the Coosa (head stream of the Alabama), flowing into the Gulf of Mexico. The streams draining the Appalachian region on the west are tributary to the Ohio River. They are they Hiwassee, the Little Tennessee, and the French Broad, which flow from the Blue Ridge through a network of high mountains, and break through the great Unaka range to the Tennessee; the Holston and Clinch rivers, also tributaries of the Tennessee; the Cumberland, the New (head of the Kanawha), the Little Kanawha, Allegheny, and
