DESCRIPTION OF THE FORMATIONS. F 2 . 79 



The northern outcrop conies in from Dauphin county just 

 below Liverpool, runs in a straight line to the Juniata, 

 where it returns eastward, as the southern limb of the syn- 

 cline, to Mt. Patrick. Ledges of rock mark its passage of 

 the Susquehanna at both places. This formation will be 

 described in detail in the reports on Liverpool, Greenwood, 

 Howe, and Buffalo townships. 



The southern or Allen's cove will be described in the re- 

 port on Penn township. 



No. XL Mauch Chunk red shale. 



Inside the two coves lie two triangular patches of the 

 Mauch Chunk red shale, the latest of the geological forma- 

 tion now remaining in the county, but as mentioned else- 

 where, not the latest that once existed there. Great parts 

 even of this have been swept away, only about 1500 feet re- 

 maining. Some of its beds are hard, and form low rounded 

 elevations not deserving the name of hills. But for the 

 most part they are soft and easily eroded. 



The red shale in the southern cove is cut by the various 

 dykes described in the report on Penn township. 



The lower part of this red shale is very calcareous in some 

 places, sufficiently so at Mt. Patrick to render hard the 

 water in the wells. But there are no limestone bands, still 

 less any indications of that sheet of lower carboniferous 

 limestone which becomes so conspicuous a feature in the 

 geology of the Southern and Western States, and corres- 

 ponds to the mountain limestone of Europe. 



The Volcanic rocks of Perry county. 



This title may appear strange at first sight, but it has 

 long been known that in the southeast of the county occur 

 some rocks of very peculiar nature, totally different from 

 any others. They cut across the line of the bedded rocks 

 quite regardless of their direction. They are very heavy, 

 intensely tough, and highly charged with iron. They are 

 in effect what the geologist calls ,; trap- rocks, v what the 

 miner call^ " elvans." They are composed of material that 

 has been fused, and forced in a fused condition into and 



