18. TYRONE TOWNSHIP. F 2 . 369 



over the Onondaga shales in the synclinal valley of Laurel 

 creek (coming from the west between Bower and Blue 

 mountain) to Mount Dempsey, where it cuts across the end 

 of the soft Clinton upper shales and turns east again. 



Receiving Montour run from the north, near Landisburg, 

 it again turns southward and curves across the synclinal of 

 Kennedy valley to the end of the Welsh hill, where it leaves 

 Tuscarora township and enters Spring. 



Receiving then McCabe's run from the west it gets round 

 the end of the mountain in the soft Onondaga lower shales, 

 and strikes for the last time southward to cross Green val- 

 ley, but after cutting through No. YI and VII and the Mar- 

 cellus soft rocks of No. VIII, it meets the hard Hamilton 

 sandstone, abandons its southeast course and keeps away 

 north eastward through Spring, Carroll, and Penn townships 

 to the Susquehanna river at Duncannon. 



[As Sherman's creek, in a small way, behaves in Tuscarora 

 and Spring townships, so, in a larger way, the Juniata and 

 Susquehanna rivers behave in crossing the middle belt of 

 the State. They avoid the greater anticlinal arches by pass- 

 ing around their dying ends ; and, as Sherman's creek gets 

 round the ends of Bower, Dempsey, and Welsh mountains 

 of Xo. IV by keeping in the softer rocks of Xo. V, yet is 

 sometimes obliged to cut gaps through the smaller lime- 

 stone and sandstone ridges of V, VI, VII, and VIII ; so 

 the Juniata and Susquehanna rivers while avoiding one hard 

 formation are obliged sometimes to cut gaps through 

 another. — J. P. L.] 



That this cutting process has not always been going on at 

 the present level of the country is evident without argument. 

 Sherman's creek and its branches, like the Juniata and Sus- 

 quehanna and all their branches, have flowed in past times 

 at various higher levels. 



I noticed round gravel lying on a hillside in Kennedy's 

 valley 60 to 80 feet above the present bed of McCabe's run. 



The Medina sandstone, No. IV. 



One long sinuous outcrop of this hard and massive for- 

 24 F\ 



