Chapter II. 



The geological structure of Perry county. 



Viewed as a whole the geological structure of Perry 

 county is the simplest possible : — about 30,000 * feet of Pal- 

 aeozoic measures, thrown into two great troughs separated 

 by one great arch. 



The northern trough extends the whole length of the 

 county, passing out south-westward into Franklin county. 



The southern trough extends half its length, passing out 

 south-westward into Cumberland county. 



The centre line of the northern trough crosses the Sus- 

 quehanna river a mile north of Mt. Patrick ; the Juniata 

 river two miles north of Newport ; and passes through the 

 villages of Juniata, Markelsville, Roseburg, Sandy Hill, 

 New Germantown, and Fairview in Toboyne township. 



The center line of the southern trough crosses the Sus- 

 quehanna river 1^ miles below Duncannon ; and passes half 

 a mile north of Shermansdale and through Oakgrove in 

 Spring township. 



The northern trough extended eastioard becomes the 

 Wiconisco anthracite coal basin of Dauphin and the Potts- 

 ville basin of Schuylkill county. 



The southern trough extended eastward becomes the 

 Dauphin county coal basin, which unites with the Wico- 

 nisco basin at Trevorton, in Schuylkill county. 



Both troughs are very deep (equally deep) at the Susque- 

 hanna river; and shoal up westward ; but not at the same 

 rate. For, while the bottoms of the troughs are exactly 

 on a level with each other at the Susquehanna and also at 

 the distance of 8 miles west of it, that of the southern 

 trough rises in the next 12 miles as much as that of the 



♦That is, counting on ly the formations which appear at the surface in Perry 

 count v. 



(31 F2.) 



