and South Central Pennsylvania. 421 



middle beds are made up of alternations of crystalline, 

 highly fossiliferons limestone and black shaly limestone. 

 There is usually no sharp distinction between the Coburn 

 limestone and the superjacent Eeedsville shale, the beds 

 toward the top of the former becoming increasingly 

 shaly and finally merging into the latter formation. The 

 upper beds of the Coburn, which are particularly char- 

 acterized by Plectambonites and Cryptolithus tessellatus, 

 become increasingly shaly toward the southeast. At 

 Coburn the typical crystalline and highly fossiliferous 

 beds are thinner than at Bellefonte and the upper beds 

 of this formation are made up of very shaly limestone 

 which is characterized by an abundance of Cryptolithus 

 tessellatus. The crystalline beds of the Coburn therefore 

 appear to thicken to the west but on the contrary become 

 increasingly shaly as they approach the old upland of 

 Appalachia to the east. 



Correlation with the Middle Ordovician Formations op 

 Eastern North America. 



It was pointed out in the first part of this paper that 

 the central Pennsylvanian province occupied, geographi- 

 cally, a somewhat intermediate position between the New 

 York, Mohawkian, or Middle Ordovician terranes on the 

 northeast and those of similar age at Chambersburg, 

 Pennsylvania. The presence in the Carlim of Bathyu- 

 rus (cf. B. extans), Columnaria (cf. C. halli), Maclurites 

 logani, and other characteristic fossils previously listed, 

 shows this formation to lie above the Beekmantown and 

 below the Trenton. Since the term Black River has now 

 become very indefinite when applied outside of New 

 York State, and since the formations subjacent to the 

 Trenton throughout the central and southern Appala- 

 chians are found to vary both f aunally and lithologically, 

 I have followed Ulrich in the use of the term Stones 

 River for the pre-Trenton group which lies above the 

 Beekmantown. Although the Salona contains one genus, 

 Brongiartiella, which has not been found anywhere else 

 in the Trenton of North America, the rest of its fauna is 

 upper Middle Ordovician in aspect. The Coburn, on the 

 other hand, contains a long list of typical Trenton fossils. 



