22 F\ REPORT OF PROGRESS. E. W. CLAYPOLE. 



(or the hard-rock outcrops must always have stood higher 

 than the soft-rock outcrops. And thus we can easily 

 imagine both the mountains and the valleys of the surface 

 of Perry county in past times standing at an elevation sev- 

 eral thousand feet higher above sea level than now ; and 

 not of Perry county only, but of all Pennsylvania, and in 

 line of all the Appalachian belt of the United States. 



The Susquehanna river has therefore a rock bed its whole 

 length past Perry county, the edges of the strata (upturned 

 sometimes towards the north, sometimes towards the south) 

 crossing it from bank to bank, and producing riffles in many 

 places, behind which lie shallow sheets of river pebbles and 

 river sand, brought down from the northern counties, and 

 from the State of New York, — pebbles moved forward by 

 the spring and fall freshets and replaced by others, — peb- 

 bles gradually being ground into mud, and to be finally 

 spread upon the bottom of Chesapeake bay and the Atlantic 

 ocean. The Duncan's island flat is an inland delta of such 

 deposits. 



In long-continued droughts the river bed is left uncovered 

 in a thousand places, and the bordering strata can be traced 

 across it, or even used for fording. After heavy general 

 rains, or after the melting of the winter snows, a sea of 

 water descends the broad channel, filling it to the top of its 

 banks ; and debacles of floating ice threaten the safety of 

 the railroad and canal which accompany its course. Mil- 

 lions of tons of rounded stones and sand are poured into it 

 by all its affluents, keeping up its supply of grinding ma- 

 terial for lowering its own bed, and furnishing the amplest 

 evidence that could be desired of the continuous destruc- 

 tion of the whole country and the continuous lowering of 

 the general surface through all ages.'" 



The JunigAa river is the principal branch of the Susque- 

 hanna in central Pennsylvania, as it drains the face of the 

 Allegheny mountain for a length of 50 miles, and also por- 



*Too muofa lias not here been said on this subject to prepare the reader for 

 the Important geological consequences of tuis process of river erosion, a good 

 understanding of which is absolutely necessary, if the descriptive geology of 

 this or any other county of Pennsylvania is to be adequately comprehended. 



