Regional and Economic Geography of Pennsylvania: Physiography .... Part I., Part 1 (Google eBook)

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University of Pennsylvania, 1906 - Physical geography - 69 pages
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Page 62 - Science, new ser., vol. 13. pp. 98-99, 1901. Discusses their formation as due to formation and persistence of local ice dams. 2. Charleston folio, West Virginia.
Page 57 - ... crest of the escarpment 2400 to 2700 feet high. The Allegheny Front crosses Pennsylvania in a sweeping curve toward the northeast for a distance of 230 miles, until it merges obscurely with the zigzags of the anthracite region in the northeastern corner of the state. The escarpment is broken only by narrow ravines through which flow the northern branches of the Susquehanna, the North Branch, Muncy, Loyalsock, Lycoming and Pine creeks, the West Branch, and Beech Creek. South of the gorge of Beech...
Page 57 - ... to a mile and a half wide, making the terrace. From the terrace there is an abrupt rise to the crest of the escarpment at 2,400 to 2,700 feet. When seen near at hand, however, the terrace looks like a broken region of irregular hills the result of dissection by numerous streams. The terrace is due to the presence of a second resistant formation, and as the crest of the Front becomes lower toward the northeast the terrace is entirely absent. The Allegheny escarpment crosses the State from...
Page 34 - ... each converge with different ridges in the opposite direction, there will result a continuous ridge looping back and forth, first in one direction, then in the other, the alternate reaches of which are roughly parallel. (Fig. 2.) To this type of ridge the name zigzag has been applied, and accordingly as the original folds were broad and gently pitching, or narrow and steeply pitching, the zigzags are long and wide or short and close together. The best example of the class is the double series...
Page 69 - ... the latter. In the central province the structural control resulted in the development of the characteristic grapevine pattern of adjusted subsequent drainage. In the plateau province the absence of structural control resulted in the development of a ramified, dendritic pattern of insequent drainage. Over the entire area the streams branch again and again, until there is hardly a square mile into which one or more has not worked its way. In the central province the hard strata stand up as sharp...
Page 47 - Fig. 1), except for the deflection by the Big and Little offsets, and maintains a height of 1,200 to 1,600 feet even with a crest at times not over fifty feet wide. Most of the other ridges are of more steeply inclined strata, giving a fairly symmetrical cross profile, except where modified by a terrace. Of the symmetrical type there is no better example than Mahantango Mountain for many miles east of the Susquehanna.
Page 44 - The streams of the region show the transverse courses of the main rivers, inherited from former cycles, with the resultant water gaps, and the subsequent streams in longitudinal adjusted courses, developed principally in the second cycle. All of the streams are entrenched in the still young present cycle; some of them in meandering courses; while the whole drainage system shows the trellis pattern characteristic of a folded mountain region of alternating hard and soft strata.
Page 45 - A Regional and Economic Geography of Pennsylvania WALTER S. TOWER PART I. Physiography : The Central Province (Concluded) The Plateau Province Location and Extent.
Page 9 - It is evident from the different stages in the formation and subsequent history of the area of which Pennsylvania is a part that the State may be divided into three natural physiographic provinces, each a part of a much larger province, and each of which is characterized by a distinct type of surface form. The divisions, as shown on the accompanying relief map (Fig. i), are...
Page 58 - Mountain, is of essentially the same character as Ligonier Valley a high upland surface broken by the deep ravines in which the streams flow. Many of the streams, flowing down from the crest of the Front, have found the slope of the surface itself nearly satisfactory, hence in the upper courses they flow in relatively shallow valleys, often not more than 100 feet deep.

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