DESCRIPTION OF THE STAUNTON SHEET. GEOGRAPHY. Illinois and Indiana. Its eastern boundary is southward to northern Georgia the Great Valley of the Staunton atlas sheet are of sedimentary sharply defined along the Appalachian Valley by is drained by tributaries of the Tennessee River, origin that is, they were deposited by water. General relations. -The area included in the the Alleghany front and the Cumberland escarp­ which at Chattanooga leaves the broad valley and, They consist of sandstone, shale, and limestone, Staunton atlas sheet is one-quarter of a square ment. The rocks of this division are almost entering a gorge through the plateau, runs west­ all presenting great variety in composition and degree, which lies between the parallels 38° and entirely of sedimentary origin and remain very ward to the Ohio. South of Chattanooga the appearance. The materials of which they are 38° 30' north latitude and the meridians 79° and nearly horizontal. The character of the surface, streams flow directly to the Gulf of Mexico. composed were originally gravel, sand, and mud, 79° 30' west longitude. This area measures which is dependent on the character and attitude Geographic divisions of the Staunton area. derived from the waste of older rocks, and the approximately 35 miles from north to south and of the rocks, is that of a plateau more or less com­ The area of the Staunton sheet is divided diagonally remains of plants and animals which lived while 27J miles from east to west, and embraces a little pletely worn down. In the southern half of the into two parts which differ in topographic char­ the strata were being laid down. Thus some of less than 938 square miles. It comprises the province the plateau is sometimes extensive and acter. The southeastern lies in the valley of the great beds of limestone were formed largely greater part of Augusta County, the southwestern perfectly flat, but it is oftener much divided by Virginia; the northwestern includes a portion of from the shells of various sea animals, and the corner of Rockingham County, the northern streams into large or small areas with flat tops. the Appalachian ranges. beds of coal are the remains of a luxuriant vegeta­ corner of Rockbridge County, and the eastern In West Virginia and portions of Pennsylvania The Great Valley region has, in greater part, a tion, which probably covered low, swampy shores. half of Highland County, Virginia, and the south­ the plateau is sharply cut by streams, leaving gently undulating surface, consisting of rounded The rocks afford a record of sedimentation ern portion of Pendleton County, West Virginia. in relief irregularly rounded knobs and ridges hills separated by meandering valleys of moderate from earliest Cambrian to Juratrias time. Their Its southeastern corner is very near the foot of which bear but little resemblance to the original depth. To the north, east, and southeast, the composition and appearance indicate at what dis­ the Blue Ridge, and it extends northwestward surface. The western portion of the plateau has high areas rise to an average altitude of 1,500 tance from shore and in what depth of water they across the Great Valley to within a few miles of been completely removed by erosion, and the sur­ feet, but to the southwestward this gradually were deposited. Sandstones marked by ripples the front of the Alleghany Mountains. face is now comparatively low and level, or rolling. increases to 2,000 feet. The very uniform alti­ and cross-bedded by currents, and shales cracked In its geographic and geologic relations this Altitude of the Appalachian province. The tudes of these higher lands define a general plain by drying on mud flats, indicate shallow water; area forms a part of the Appalachian province, Appalachian province as a whole is broadly dome- which formerly extended over the entire valley while limestones, especially by the fossils they which extends from the Atlantic coastal plain on shaped, its surface rising from an altitude of about region. The minor drainage systems have cut contain, indicate greater depth of water and the east to the Mississippi lowlands on the west, 500 feet along the eastern margin to the crest of channels in this old plain, giving rise to the scarcity of sediment. The character of the and from central Alabama to southern New York. the Appalachian Mountains, and thence descend­ present diversity of surface, but the former level adjacent land is shown by the character of the All parts of the region thus defined have a com­ ing westward to about the same altitude on the is widely preserved on the hilltops. There are a sediments derived from its waste. Coarse sand­ mon history, recorded in its rocks, its geologic Ohio and Mississippi rivers. few scattered knobs, such as Betsey Bell, Mary stones and conglomerates, such as are found in the structure, and its topographic features. Only a Each division of the province shows one or Gray, and the Sugar Loaf, which rise above the Coal Measures, were derived from high land, on part of this history can be read from an area so more culminating points. Thus the Appalachian former level. which stream grades were steep, or they may have small as that covered by a single atlas sheet; Mountains rise gradually from less than 1,000 feet The Great Valley is bounded on the west by resulted from wave action as the sea encroached hence it is necessary to consider the individual in Alabama to more than 6,600 feet in western the Little North Mountain and the foothills of upon a sinking coast. Red sandstones and shales, sheet in its relations to the entire province. North Carolina. From this culminating point the Narrowback range. These generally present such as make up some of the Cambrian and Subdivisions of the Appalachian province. they decrease to 4,000 or 3,000 feet in southern an abrupt and almost continuous wall to the east­ Silurian formations, result from the revival of The Appalachian province may be subdivided Virginia, rise to 4,000 feet in central Virginia, and ward. In the central part of the area the Little erosion on a land surface long exposed to rock into three well-marked physiographic divisions, descend to 2,000 or 1,500 feet on the Maryland- North Mountain is low and is crossed by several decay and oxidation, and hence covered by a deep throughout each of which certain forces have pro­ Pennsylvania line. gaps, but southward it rises as a rough, rocky residual soil. Limestones, on the other hand, if duced similar results in sedimentation, in geologic The Appalachian Valley shows a uniform increase range to a relatively level crest-line nearly 3,000 deposited near the shore, indicate that the land structure, and in topography. These divisions in altitude from 500 feet or less in Alabama to feet high. It is depressed at Pond Gap to about was low and that its streams were too sluggish to extend the entire length of the province, from 900 feet in the vicinity of Chattanooga, 2,000 feet 2,700 feet, and at Buffalo Gap to 1,850 feet, or carry off coarse sediment, the sea receiving only northeast to southwest. at the Tennessee-Virginia line, and 2,600 or 2,700 almost to its base. Narrowback Mountain fine sediment and substances in solution. The central division is the Appalachian Valley. feet at its culminating point, on the divide between averages 2,500 feet in altitude, and is separated The sea in which these sediments were laid It is the best defined and most uniform of the the New and Tennessee rivers. From this point it from the low, northern range of Little North down covered most of the Appalachian province three. In the southern part it coincides with the descends to 2,200 feet in the valley of New River, Mountain by an offset in which there is a cross and the Mississippi basin. The area of the belt of folded rocks which forms the Coosa Valley 1,500 to 1,000 feet in the James River basin, and valley having an altitude of 1,600 feet. It is Staunton sheet was near its eastern margin at of Georgia and Alabama and the Great Valley-of 1,000 to 500 feet in the Potomac basin, remaining crossed by North River and Briery Branch gaps, certain stages of sedimentation, and the materials East Tennessee and Virginia. Throughout the about the same through Pennsylvania. These very nearly at the general level of the Great of which its rocks are composed were probably central and northern portions the eastern side only figures represent the average elevation of the Valley. derived largely from the land to the east. The is marked by great valleys such as the Shen­ valley surface, below which the stream channels West of Little North Mountain lies a succes­ exact position of the eastern shore-line of this andoah Valley, of Virginia, the Cumberland Valley are sunk from 50 to 250 feet, and above which sion of high, more or less continuous ranges ancient sea is not known, but it probably varied of Maryland and Pennsylvania, and the Lebanon the valley ridges rise from 500 to 2,000 feet. extending from northeast to southwest. The first from time to time within rather wide limits. Valley of northeastern Pennsylvania the west­ The plateau, or western, division increases in is the Great North Mountain, which culminates Three great cycles of sedimentation are recorded ern side being a succession of ridges alternating altitude from 500 feet at the southern edge of the in Elliott Knob at 4,473 feet above sea-level, the in the rocks of this region.