Description of the Pikeville Sheet

DESCRIPTION OF THE PIKEVILLE SHEET. GEOGRAPHY. boundary is sharply defined along the Appala westward in a deep, narrow gorge through the tions, heading upon the immediate edge of the chian Valley by the Alleghany front and the Cumberland Plateau into the Ohio River. From valley. General relations. The Pikeville atlas sheet Cumberland escarpment. The rocks of this divi New River southward to northern Georgia the The foregoing description and an examination comprises an area bounded by the parallels 35° sion are almost entirely of sedimentary origin and Great Valley is drained by tributaries of the Ten of the topographic map show that in this region 30'"and 36° and the meridians 85° and 85° 30'. remain very nearly horizontal. The character of nessee River, which at Chattanooga leaves the there are two plains whose surfaces are nearly The region mapped embraces, therefore, a quarter the surface, which is dependent on the character broad valley and, entering a gorge through the parallel and are separated by a vertical distance of a square degree of the earth's surface. Its and attitude of the rocks, is that of a plateau plateau, runs westward to the Ohio. South of of about 1,000 feet. The lower plain is apparent dimensions are 34.5 miles from north to south more or less completely dissected, or, elsewhere, Chattanooga the streams flow directly to the Gulf in the level portions of the highland rim, in the and 28 miles from east to west, and it contains of a lowland. In the southern half of the prov of Mexico. Sequatchie Valley, and in the Tennessee Valley. nearly 980 square miles. The adjacent atlas ince the surface of the plateau is sometimes TOPOGRAPHY. The upper plain is the general surface of the sheets are Standing Stone on the north, Kingston extensive and perfectly flat, but oftener it is much plateau, below which the streams flow in more or on the east, Chattanooga on the south, and cut by stream channels into large or small, flat- The country embraced by the atlas sheet lies less deeply cut channels and above which rise a McMinnville on the west. The area lies wholly topped hills. In West Virginia and portions of almost wholly within the western division of the few isolated hills or mesas. within the State of Tennessee and contains por Pennsylvania the plateau is sharply cut by its Appalachian province, as above defined. Its Areas of these two plains have been recognized tions of White, Cumberland, Van Buren, Grimdy, streams, leaving in relief irregularly rounded extreme southeastern portion lies in the great over nearly the entire Appalachian province, sepa Sequatchie, Bledsoe, and E-hea counties. knobs and ridges which, bear but little resem Appalachian Valley, here occupied by the Ten rated by a varying vertical distance, and their In its geographic and geologic relations this blance to the original surface. The western por nessee River, and the Sequatchie Valley also relations throw much light upon the history of area forms a part of the Appalachian province, tion of the plateau has been completely removed crosses its southeastern corner. The latter is the province during the later geologic ages. This which extends from the Atlantic coastal plain on by erosion, and the surface is now comparatively located upon the westernmost of the sharp folds region formerly stood much lower than now, so the east to the Mississippi lowlands on the west low and level, or rolling. which characterize the central division, and might that the present plateau, the higher plain, was and from central Alabama to southern New York. Altitude of the Appalachian province. The properly be regarded as its western limit, except near sea-level. The land was worn down by All parts of the region thus denned have a com Appalachian province as a whole is broadly that Walden Ridge, lying to the eastward, has all streams flowing upon its surface till it was mon history, recorded in its rocks, its geologic dome-shaped, its surface rising from an altitude of the characteristics of the western or plateau reduced to a nearly even plain, with only here and structure, and its topographic features. Only a of about 500 feet along the eastern margin to the division. The greater portion of the area of the there a low hill remaining where the rocks were part of this history can be read from an area so crest of the Appalachian Mountains, and thence sheet is occupied by the Cumberland Plateau and unusually hard or where they were protected small as that covered by a single atlas sheet; descending westward to about the same altitude its outlier, Walden Ridge. The plateau here has from erosion by their position. Since the surface hence it is necessary to consider the individual on the Ohio and Mississippi rivers. an altitude varying from 1,700 to 1,900 feet. was not perfectly reduced this is called a pene- sheet in its relations to the entire province. Each division of the province shows one or Above this general level rise small isolated hills plain, and since it was formed near the lowest /Subdivisions of the Appalachian province. more culminating points. Thus the Appalachian or mesas from 100 to 500 feet higher. These possible level of erosion it is called a baselevel The Appalachian province may be subdivided Mountains rise gradually from less than 1,000 feet appear as hills rising above a level plain. The peneplain. After the surface of the land had into three well-marked physiographic divisions, in Alabama to more than 6,600 feet in western western side of the plateau is extremely irregular. become reduced nearly to sea-level this region was throughout each of which certain forces have pro North Carolina. From this culminating point The streams that drain its surface have their elevated about 1,000 feet and at the same time duced similar results in sedimentation, in geologic they decrease to 4,000 or 3,000 feet in southern sources within a short distance of the Sequatchie tilted southward. The streams, which had become structure, and in topography. These divisions Virginia, rise to 4,000 feet in central Virginia, Valley, flow westward in shallow channels for sluggish, were at once stimulated to renewed extend the entire length of the province, from and descend to 2,000 or 1,500 feet on the Mary several miles, and then plunge into deep, narrow activity and began rapidly to sink their channels northeast to southwest. land-Pennsylvania line. canyons which they have carved within the pla into the peneplain. Erosion progressed most The central division is the Appalachian Valley. The Appalachian Valley shows a uniform teau. Numerous remnants of the plateau, almost rapidly upon soft rocks, so that on the western It is the best denned and most uniform of the increase in altitude from 500 feet or less in Ala or quite isolated, fringe its western side. part of this area, where the sandstone capping was three. In the southern part it coincides with the bama to 900 feet in the vicinity of Chattanooga, Walden Ridge, as already stated, has most thin, and in the Sequatchie anticline, where lime belt of folded rocks which forms the Coosa Valley 2,000 feet at the Tennessee-Virginia line, and of the characteristics of the plateau west of stone formed the surface, the streams quickly sunk of Georgia and Alabama and the Great Valley of 2,600 or 2,700 feet at its culminating point, on Sequatchie Valley. It is somewhat higher, hav their channels down nearly to the new baselevel East Tennessee and Virginia. Throughout the the divide between the New and Tennessee rivers. ing an altitude between 1,900 and 2,000 feet. of erosion, and then, by broadening their valleys, central and northern portions the eastern side From this point it descends to 2,200 feet in the Its streams rise near the edge of the Sequatchie began the formation of a new peneplain. The only is marked by great valleys such as the valley of New River, 1,500 to 1,000 feet in the Valley and flow southeastward in shallow chan old peneplain was preserved at the higher level Shenandoah Valley of Virginia, the Cumberland James River basin, and 1,000 to 500 feet in the nels until near the eastern escarpment, where they where the hard rocks capped the plateau. After Valley of Maryland and Pennsylvania, and the Potomac basin, remaining about the same through plunge into narrow gorges. the formation of the second peneplain was well Lebanon Valley of northeastern Pennsylvania Pennsylvania. These figures represent the average The northwestern portion of the area of the advanced upon areas of soft rocks, the region was the western side being a succession of ridges alter elevation of the valley surface, below which the sheet lies within the highland rim of middle again lifted and the streams began cutting their nating with narrow valleys. This division varies stream channels are sunk from 50 to 250 feet, Tennessee. The surface is somewhat rolling, but present channels within the last-formed peneplain. in width from 40 to 125 miles. It is sharply out and above which the valley ridges rise from 500 in general has an altitude of less than 1,000 feet. GEOLOGY. lined on the southeast by the Appalachian Moun to 2,000 feet. The slopes between this lower plain and the STRATIGRAPHY. tains and on the northwest by the Cumberland The plateau, or western, division increases in plateau are very abrupt, the upper portions being Plateau and the Alleghany Mountains.

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