18. TYRONE TOWNSHIP. F\ 371 



has been eroded along the outcrop of the soft lower green 

 shales. This trench-like valley drains out through a gap 

 in the lower rampart-like ridges of the two sandstones. The 

 same structure prevails along the whole line, but is nowhere 

 else so conspicuous. 



The outer wall, or sandstone ridge, is, as described above, 

 double crested ; the one crest formed by the Iron sandstone, 

 the other by the Ore sandstone. 



The upper green shales, which lie between the two sand- 

 stones, are usually less than 200 feet thick, and are protected 

 from the weather by the covering of slabs of the almost in- 

 destructible Iron sandstone. 



Xo trace, so far as I have observed, exists of the ore beds 

 which in some other places, as at Millerstown, lie under the 

 Ore sandstone and in the upper shale. 



The Sandvein ore bed, on top of the Ore sandstone, is 

 present and makes a fair display, especially in Kennedy's 

 valley, where on the land of Mr. Egolf, numerous fragments 

 may be seen containing characteristic Clinton fossils. 



The Onondaga group, ( V.) 



The shales of this group crop out over the greater 

 part of Tyrone township and yield the colored soil which it 

 usually exhibits. They are everywhere on edge, so that 

 their thickness is exposed in many places. It is not easy 

 to obtain measurements on account of the difficulty of de- 

 termining the exact limits of the beds. Near Landisburg, 

 however, exposures occur sufficiently clear for the purpose. 

 On the whole, Tyrone township affords one of the most in- 

 structive fields for studying the Onondaga group that I 

 have found in the count\ r . 



The Bloomsburg red shale is well exposed to the south 

 of the town on the road to Bridgeport, and measurements 

 give its thickness there at about 700 feet — the same as else- 

 where. This part of the group is uniform in mass over the 

 county. 



The variegated shale, as nearly as it was possible to de- 

 termine the fact, is here of nearlv the same thickness as in 



