294 CAMPBELL — NORTH PENNSYLVANIA AND SOUTH NEW YORK 



to an altitude of about 1,300 feet in the southwestern corner of the Kit- 

 tanning quadrangle in Butler county, 1,400 feet along a line extending 

 from the northwest corner of the Kittanning to the southeast corner of 

 the Rural Valley quadrangle, and to 1,500 feet along Redbank creek in 

 the northeastern part of the latter area. 



The northward rise is apparent also along the western face of Chest- 

 nut ridge in the group of quadrangles which previously has been men- 

 tioned as lying in the Monongahela valley and in the Latrobe and 

 Indiana quadrangles adjacent on the northeast. About Indiana the 

 peneplain was not extensive^ developed. The region is located away 

 from the main drainage lines, and the conditions of erosion were not so 

 favorable as they were in the Monongahela valley ; moreover, the rocks 

 appearing at the surface are more sandy, and they were not eroded to 

 the same extent as in the other locality. Nevertheless the peneplain 

 surface seems to be well marked on the present divide between the 

 streams flowing into the Conemaugh river on the south and the minor 

 tributaries of the Alleghen}^ river on the west. This territory has been 

 the scene of several cases of stream piracy.* The streams formerly flow- 

 ing into Conemaugh river have been beheaded by Crooked creek, which 

 is a tributary of the Allegheny river. The reason for this change is not 

 apparent, but the fact that the change has been accomplished is with- 

 out question. Since such changes usually occur on the rejuvenation of 

 the streams after a period of extensive baseleveling, it seems altogether 

 probable that the present divide, which was formerly an old channel of 

 the captured stream, marks the general level of the peneplain. Accord- 

 ing to that criterion, its altitude is about 1,400 feet above scale vel. 



North of this point there is little available evidence to show the extent 

 and altitude of the Harrisburg peneplain. Judging, however, from its 

 development in southwestern Pennsylvania and eastern Ohio, it seems 

 probable that it is present in the Girard and Erie quadrangles, in the 

 northwestern part of the State. The uplands in this region are composed 

 of not very resistant rocks, and it seems highly probable that they w^ere 

 reduced during this cycle of erosion. The altitude of these tops is about 

 1,300 feet. 



Thus it appears that the plateau surface developed on the Chemung 

 rocks of northern Pennsylvania and southern New York resembles the 

 Harisburg peneplain in that they are both peneplains of rather extensive 

 development, involving most of the region except that occupied by the 

 most resistant rocks; also the origin of both seemingly post-dates the 

 Jura-Cretaceous cycle of reduction, and they are both manifestly older 

 than the Somerville peneplain, which is developed only on the softest 



* George B. Richardson : Geologic Atlas of the United States, Indiana folio, in press. 



