... The Physiographic Features of Maryland

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Jones & Kroeger, printers, 1900 - Physical geography - 28 pages
 

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Page 20 - Catoctin, seems never to have been reduced to such a valley lowland as formerly existed along Catoctin creek. The combined action of the resistant rocks to the north, and the superior powers possessed by the headwaters of Catoctin creek working up from the south has, so far, resulted in confining the drainage of the northern streams within comparatively narrow bounds. Altho the volumes of the latter streams have thus been limited to such meagre proportions, small subsequent streams and valleys along...
Page 22 - Sufficient time, however, was not allowed for the reduction of the ridges also, as was the case during the preceding cycle. It was at this time that the level floor of the Great Valley was produced, the general surface of which can be followed in and out among these western ridges. This generally even and accordant surface is often referred to as the Shenandoah Plain, because it is so typically developed over the yielding rocks of the Shenandoah Valley. Having been developed only in the vicinity...
Page 27 - ... features of advanced topographic maturity and perhaps even become a peneplain. This period of repose was closed by a decided warping of the new surface, that raised it to an elevation of about two thousand feet in Western Maryland, but only to about three hundred feet in the central portion of the state. Then followed another period of repose during which the Shenandoah Plain was carved out. Finally a series of elevations at irregular intervals has warped the two plains still further, bringing...
Page 17 - Guided by the easier piths thus opened, certain rivers extended their courses, not along constructional troughs or synclines, but along the axial lines of the arches or anticlines. Along the axis of a comparatively broad flat anticline in Garrett county the two branches of the Savage river have thus opened the broad depression lying between Savage and Meadow mountain.
Page 24 - Tennessee, Kentucky, Virginia, West Virginia, Maryland and Pennsylvania into New York, where it forms the high lands covering the southern half of the state from the Catskills to Lake Erie. This plateau, which preserves, in its general level, the largest continuous areas of the Jura-cretaceous, or Schooley peneplain, is not characterized by a broad, unbroken expanse, but has been so deeply dissected that only the even crests of isolated ridges remain to indicate the former extent of the plateau....
Page 19 - Its prominence is due to the greater resistance of the heavy Cambrian quartzite, which has withstood the attacks of the elements more successfully than the rocks on either flanks. Again it is with the Catoctin as with the Blue Mountain, that that slope which descends to the yielding rocks of the broad valley lowlands, is the longer and the more precipitous, while the opposite slope is the milder and the shorter. Here, however, the valley lowland is that of the Frederick or Monocacy valley carved...
Page 21 - ... the quality of land varies ; white clay and loam, with red clay subsoil, black loam and sandy ; oak and pine timber and some hickory. Alleghany : limestone and slate ; mountain land rocky and gravelly ; pine, oak, walnut, and poplar. Washington : limestone land, and very productive in the valley lying between the Blue Ridge on the east and the North Mountain on the west ; west of North Mountain the land is slate and not so productive. Montgomery : clay loam, very thin, much of it exhausted from...
Page 27 - ... point of view also there are two classes of streams here; first, those which flow westward down the general dip of the strata to the Ohio, and second, those which flow eastward against the general dip to the Atlantic. The Youghiogheny and Castleman rivers take out all the Ohio drainage, while the Savage and the North Branch of the Potomac lead off the waters which flow into the Atlantic. It has already been pointed out that the whole Appalachian district formerly bore the relation of a coastal...
Page 21 - Below these valleys, particularly near the mountain fronts, the torrent-like streams have often cut steep, wild gorges. thus has a width of about seventy-three miles. As has been noticed above, the Greater Valley admits of a two-fold sub-division into the Great or Cumberland Valley on the east and the zone of the Alleghany ridges on the west. The Great or Cumberland Valley is the rather broad, even depression lying between the Blue Ridge on the east and the North Mountain on the west. This broad...
Page 26 - ... all these streams increased activity and they began to actively reduce their valleys to the new base-level. Today the new valley-floors thus produced may still be seen as flat-topped hills of Hampshire and Jennings shales bounded by steep and often precipitous cliffs which are capped by rocky crags of Pocono sandstone. Perhaps the largest area covered by this surface of denudation is to be found in the vicinity of Accident. This town is located near the centre of a broad amphitheater, whose boundaries...

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