278 CAMPBELL — NORTH PENNSYLVANIA AND SOUTH NEW YORK 



of establishing the dates of origin of the topographic features of the region. 

 Doubtless this lack of attention in the past was due to the absence of 

 adequate maps, but in a large measure these are being supplied, and 

 now it is possible, by the aid of the topographic sheets at hand, to study 

 the surface features of the region and provisionally to correlate them 

 with similar features of known age in other parts of the country. 



Description of the Region 



One of the best regions for physiographic study is embraced in the 

 Tioga, Elkland, and Gaines quadrangles in Tioga and Potter counties, 

 Pennsylvania. Erosive conditions in this region presumably have been 

 similar to those prevailing over most of the plateau in question, and con- 

 sequently the topography may be regarded as the type of the region. A 

 careful study of this topography shows that the descriptions already given 

 of the topographic features are not quite correct, and that instead of being 

 simply a deeply dissected plateau surface it really consists of a dissected 

 plateau upon which stand distinctly higher ridges with comparatively^ 

 flat tops. It seems probable, therefore, that the physiographic history 

 of the region is complex and similar to that which has prevailed in the 

 eastern part of the state. 



The rocks composing the plateau region of northern Pennsylvania and 

 southern New York are fairly homogeneous. The formations involved 

 are those which constitute the upper part of the Devonian and the lower 

 part of the Carboniferous series. In a general way the rocks may be 

 divided into two classes, which differ in their hardness and in their re- 

 sistance to the action of erosion. The softer rocks belong to the Chemung 

 formation ; they are shaly and somewhat calcareous, and consequently 

 are reduced with comparative ease. Above the Chemung rocks occur 

 the more sandy Catskill-Pocono beds and also the very resistant sand- 

 stones of the Pottsville formation. The softer Chemung beds are ex- 

 posed in outcrop on all the anticlines of the region, and the harder beds 

 overlying them are present in all of the synclinal troughs. 



Although deeply dissected, the Chemung hilltops on the anticlinal 

 tracts have remarkable uniformity in altitude — a fact which at once 

 suggests a dissected peneplain. Not only do the hilltops of one anti- 

 clinal region rise to a common height, but there is an agreement between 

 the upland surface of adjacent anticlines to such an extent that it seems 

 impossible to avoid the conclusion that they are parts of one extended 

 peneplain which was developed on the softer rocks of the region. This 

 supposition is also borne out by the character of the hilltops, which are 

 generally rounded and in many cases are almost absolutely flat. 



