IS. TYRONE TOWNSHIP. F\ 367 



18. Tyrone toicnship. 



Tyrone township is bounded on the north, east, and west 

 by straight lines. Its southern boundary follows the curves 

 of the crest of the Blue mountains. (See map.) After 

 ranging in almost a straight line from the Susquehanna 

 river westward for about 20 miles, it doubles back eastward 

 for two miles to the knob of Welsh hill, thence southwest- 

 ward, five miles to the head of Kennedy 's valley, around 

 which it bends sharply and returns to Pilot Knob (Mount 

 Dempsey) overlooking Landisburg, thence southwestward 

 again two miles to the Madison township corner. 



Bower mountain. Mount Dempsey, and Welsh hill are 

 made by three great arches (anticlinals) of Medina sandstone, 

 Xo. IV. of different heights. (See cross-section Fig. 1, 

 Plate XLIII.) 



These mountains have long sloping ends towards the 

 northeast, that is, into the township, because the anticlinal 

 arches are sinking in that direction, and the soft Clinton and 

 Onondaga rocks fold over and around the lower levels of 

 these slopes. 



The whole drainage of the township is accomplished by 

 Sherman's creek and its branches iiowing east-southeast- 

 ward across the ends of the three mountains. In this fea- 

 ture of its geography, Tyrone township exemplifies the 

 drainage-system of middle Pennsylvania. 



Sherman's creek, on entering the township from the west, 

 cuts through a high ridge of the Onondaga upper lime beds 

 and gets into the lower shales. Further than this it cannot 

 go, being confronted by the Iron sandstone of Bower 

 mountain. So it turns and flows east until it can get round 

 the end of the mountain, still keeping in the soft shales. 



Receiving Muddy run from the north it strikes south 



