280 CAMPBELL — NORTH PENNSYLVANIA AND SOL^TH NEW YORK 



In a recent description of the topography of the slate belts of Lehigh 

 county, Dale* recognizes the upper peneplain, but he makes no effort 

 to determine its extent or its date of origin. 



It seems to the writer, therefore, that there is undoubted evidence of 

 the existence of a peneplahi other than the Somerville or Schooley, and 

 also that the newl}^ recognized peneplain lies about 300 feet above the 

 Somerville plain, and consequently is a much older feature. 



SCHUYLKILL VALLEY 



In passing to the southwest these two features are easily recognized 

 along the Schuylkill river in the vicinity of Reading. The limestone 

 be]^ is narrow at this point, and consequently^ the lower plain is not 

 extensively developed, but it is present at an altitude of about 300 feet 

 above sealevel. The Hudson shale has an extensive geographic devel- 

 opment northwest of Reading, and fortunately there is an excellent con- 

 tour map from which to study the character and altitude of the surface. 

 On the Wernersville quadrangle the country l3ang north of the narrow 

 valley contains scarcely any level land. It is made up entirely of small 

 hills, which, as a rule, stand at an altitude of about 500 feet above sea- 

 level. Where harder rocks occur, the hills stand up as monadnocks 

 above this common level to altitudes as high as 800 feet, but these are 

 clearly above the general hilltop level. The line of demarkation between 

 the monadnocks and the surface of the peneplain is well shown west of 

 Bernville, where a small ridge rises abruptl}^ from a platform at about 

 the 500-foot contour. When it is considered that the rocks of this belt 

 are considerably disturbed, and that they consist of a heterogeneous 

 mass of shales, it is impossible to account for the regularity of the hill- 

 tops on any other hypothesis than that of baseleveling. 



SUSQUEHANNA VALLEY 



West of the Wernersville quadrangle the valley has not been mapped 

 with sufficient care to bring out the details of the surface features, but 

 in the Lebanon quadrangle the surface of the shale belt appears to range 

 from 500 to 600 feet above sealevel. The Somerville plain is not repre- 

 sented in this region, either on account of the hardness of the limestone 

 or of the distance from the major drainage lines ; but it is well devel- 

 oped on the southern belt of limestone in the vicinity of Lancaster at an 

 altitude of about 350 feet. Similar features show in the Hummellstown 

 quadrangle, the Somerville plain being slightly developed along Swatara 

 creek. The surface of the shale belt on the north side of the valley 



*Slatington folio, U. S. Geol. Survey. In press. 



