DESCRIPTION OF THE ROAN MOUNTAIN QUADRANGLE By Arthur Keith. GEOGRAPHY. have been changed to slates, schists, or similar to the Ohio. The northern portion of the eastern section. The grades of the other rivers are those rocks by varying degrees of metamorphism, or or Appalachian Mountain division is drained east­ generally prevailing in the Mountains. All the GENERAL RELATIONS. igneous rocks, such as granite and diabase, which ward to the Atlantic, but south of New River all rivers leave the border of the Mountains at 1500 Location. The Roan Mountain quadrangle lies have solidified from a molten condition. except the eastern slope is drained westward by to 1600 feet above sea. Their subsequent grades mainly in Tennessee, but about one-fourth of its The western division of the Appalachian prov­ tributaries of the Tennessee or southward by tribu­ are exceptionally steep for rivers in the limestone southern part is in North Carolina. It is included ince embraces the Cumberland Plateau, the Alle­ taries of the Coosa. districts, and not far below the Mountains they between parallels 36° and 36° 30' and meridians gheny Mountains, and the lowlands of Tennessee, The position of the streams in the Appalachian descend through narrow canyons where erosion is 82° and 82° 30', and contains about 963 square Kentucky, and Ohio. Its northwestern boundary Valley is dependent on the geologic structure. In most active. miles, divided between Washington, Sullivan, Car­ is indefinite, but may be regarded as an arbitrary general they flow in courses which for long dis­ Topography. There are many differences in the ter, and Unicoi counties of Tennessee and Yancey line coinciding with the eastern boundary of the tances are parallel to the sides of the Great Valley, surface forms of this quadrangle. The variations and Mitchell counties of North Carolina. Mississippi embayment as far up as Cairo, and following the lesser valleys along the outcrops of in the topography result largely from the varying In its geographic and geologic relations this then crossing the States of Illinois and Indiana. the softer rocks. These longitudinal streams empty influence of erosion on the different formations. quadrangle forms part of the Appalachian prov­ Its eastern boundary is sharply defined along the into a number of larger, transverse rivers, which Such rock-forming minerals as carbonates of lime ince, which extends from the Atlantic Coastal Plain Appalachian Valley by the Allegheny Front and cross one or the other of the barriers limiting the and magnesia, and, to a less extent, feldspar, are on the east to the Mississippi lowlands on the west, the Cumberland escarpment. The Cumberland valley. In the northern portion of the province removed in solution by water. Rocks containing and from central Alabama to southern New York. Plateau, Allegheny Mountains, and associated they form Delaware, Susquehanna, Potomac, James, these minerals in large proportions are therefore All parts of the region thus denned have a common plateaus are called the Appalachian Plateau. The and Roanoke rivers, each of which passes through subject to decay by solution, which disintegrates history, recorded in its rocks, its geologic structure, rocks of this division are almost entirely of sedi­ the Appalachian Mountains in a narrow gap and the rock and leaves the insoluble matter less firmly and its topographic features. Only a part of this mentary origin and remain very nearly horizontal. flows eastward to the sea. In the central portion united. Frost, rain, and streams break up and history can be read from an area so small as that The character of the surface, which is dependent on of the province, in Kentucky and Virginia, these carry off this insoluble remainder, and the surface represented on a single atlas sheet; hence it is neces­ the character and attitude of the rocks, is that of a longitudinal streams form New (or Kanawha) is thus worn down. According to the nature and sary to consider the individual area in its relations plateau more or less completely worn down. In River, which flows westward in a deep, narrow amount of the insoluble matter, the rocks form to the entire province. the southern half of the province the plateau is in gorge through the Cumberland Plateau into Ohio high or low ground. Calcareous rocks, of which /Subdivisions of the Appalachian province. The places extensive and perfectly flat, but it is more River. From New River southward to northern the least residue remains, occupy the low ground. Appalachian province is composed of three well- commonly much divided by streams into Large or Georgia the Great Valley is drained by tributaries Such are the various limestones and many of the marked physiographic divisions, throughout each of small areas with flat tops. In West Virginia and of Tennessee River, which at Chattanooga leaves shale formations. Most of these rocks leave only which certain forces have tended to produce similar portions of Pennsylvania the plateau is sharply the broad valley and, entering a gorge through the a fine clay after solution. The Shady limestone results in sedimentation, in geologic structure, and cut by streams, leaving in relief irregularly rounded Cumberland Plateau, runs westward to the Ohio. and Knox dolomite leave also, besides the clay, in topography. These divisions extend the entire knobs and ridges which bear but little resemblance South of Chattanooga the streams flow directly to a large quantity of silica in the form of chert, length of the province, from northeast to southwest. to the original surface. The western portion of the the Gulf of Mexico. which strews the surface with lumps and retards The central division is the Appalachian Valley. Plateau has been completely removed by erosion, and the process of removal. The upper layers of the DETAILED GEOGRAPHY OF THE QUADRANGLE. It is the best defined and most uniform of the the surface is now comparatively low and level, or dolomite contain less chert, and the surface which three. In the southern part it coincides with the rolling. Geographic divisions. Two of the major divi­ they form is further reduced than the lower part belt of folded rocks which forms the Coosa Valley Altitude of the Appalachian province. The sions of the Appalachian province are represented of the dolomite. The least soluble rocks are the of Georgia and Alabama and the Great Valley of Appalachian province as a whole is broadly dome within the limits of the Roan Mountain quadran­ quartzites, sandstones, and conglomerates and since East Tennessee and Virginia. Throughout the cen­ shaped, its surface rising from an altitude of about gle. The Appalachian Valley occupies about 350 most of their mass is left untouched by solution, tral and northern portions the eastern side only is 500 feet along/the eastern margin to the crest of square miles in the northwestern part of the quad­ they are the last to be reduced in height. An marked by great valleys such as the Shenandoah the Appalachiah\Mountains and thence descending rangle, the remainder being covered by the Appa­ apparent exception to this rule is formed by the Valley of Virginia, the Cumberland Valley of westward to about the same altitude on Ohio and lachian Mountains. The Valley area lies on the Cranberry granite, for it contains much soluble Maryland and Pennsylvania, and the Lebanon Mississippi rivers. southeastern border of the great Appalachian Val­ matter in feldspar, and yet maintains great heights. Valley of eastern Pennsylvania the western side Each division of the province shows one or ley, which stretches for hundreds of miles north­ For this result, the immense mass of the formation being a succession of ridges alternating with narrow more culminating points. Thus the Appalachian eastward and south west ward. In this quadrangle and the insolubility of its quartz are largely valleys. This division varies in width from 40 to Mountains rise gradually from less than 1000 feet the Valley is very irregular in outline and con­ responsible. 125 miles. It is sharply outlined on the southeast in Alabama to more than 6700 feet in western tains several ranges, such as Holston and Buffalo Erosion of the sedimentary formations has pro­ by the Appalachian Mountains and on the north­ North Carolina. From this culminating point mountains, which project from the main mountain duced a series of long ridges separated by narrow west by the Cumberland Plateau and the Alle­ they decrease to 4000 or 3000 feet in southern mass. The Mountain area consists of a group valleys that closely follow the belts of rock. This gheny Mountains. Its rocks are almost wholly Virginia, rise to 4000 feet in central Virginia, and of ranges designated by the general term Unaka structure is conspicuously notable in the limestone sedimentary, and are in large measure calcareous. descend to 2000 or 1500 feet on the Maryland- Mountains, which border the Valley with a general valleys and quartzite mountains near Erwin and The strata, which must originally have been nearly Pennsylvania line. northeasterly course. These ranges ai:e cut at many Hampton, and is shown in figs. 10 and 12 of the horizontal, now intersect the surface at various The Appalachian Valley shows a uniform points by stream gaps and include Holston, Iron, illustration sheets. Where the formations spread angles and in narrow belts. The surface features increase in altitude from 500 feet or less in Stone, Unaka, Buffalo, Cherokee, and Bald moun­ out with a low dip the valleys and ridges are vary with the outcrops of different kinds of rock, Alabama to 900 feet in the vicinity of Chatta­ tains. Southeastward from these ranges, trending broad, and where the strata dip steeply the val­ so that sharp ridges and narrow valleys of great nooga, 2000 feet at the Tennessee-Virginia line, toward the Blue Ridge, extend various cross ranges, leys are narrower.