DESCRIPTION OF THE FORMATIONS. F\ Gl 



gree of minuteness, but there is a general resemblance which 

 is not to be overlooked. In a palseontological sense also 

 there is both agreement and discrepancy. 



In the Lewistown massive limestone very few fossils can 

 be found in Perry county, and the only one that can be 

 looked for with any reasonable expectation of success at 

 most exposures is the little Leperditia alta, Conrad. As 

 this species has thus far not been seen in any of the higher 

 divisions, but ranges downward to a great distance, it can- 

 not be called a special characteristic of this limestone in the 

 county. 



In Xew York the Water-Lime is characterized by this 

 Leperclitia, and by several other species, among which is 

 Tentaculites ornatus, Hall, (= T. gyracanthus, Eaton ; T. 

 irregularis, Hall,) a species which in Perry county occurs 

 at a higher level (see section) with Spirifera Vanuxemi, 

 Hal],(=Ort7iis plicata Yanuxem.) 



The lime shales of Perry county correspond well in a gen- 

 eral way with the Lower Pentamerus limestone and the 

 Delthyris shaly limestone of New York, though, on de- 

 scending into minute details, the resemblance is less close. 

 This is, however, no more than should be expected con- 

 sidering the distance that separates the two places. We 

 have in both the same profusion of fossils, the calcareous 

 composition of the rocks, and, to a great extent, the same 

 species prevailing on slightly different horizons. The fol- 

 lowing partial catalogue will show the general resemblance 

 between the faunas of the two States. 



Partial list of fossils common to the lime sliales of Perry 

 county, Pennsylvania, and the Lower Pentamerus lime- 

 stone and Shaly limestone of New York : 



Discina discus, Hall. Meristella Icevis, Vanuxem. 

 Strophomeria rugosa, Dalman. " bella, Hall. 



Rensselceria mutabilis. Hall. Merjambonia avicaloidea, Hall. 



Rhynchonella nucleolata, Hall. Murchisonia minuta. Hall. 

 " formosa, Hall. 



This list might be much extended by further study and 

 collection. The total absence of the genera Platyceras and 



