228 J. J. STEVENSON CARBONIFEROUS OF APPALACHIAN BASIN 



in all 1,194 feet to the Pottsville. The fossils were obtained from the 

 Mill Creek limestone, which is about 700 feet above the Baltimore coal 

 bed; the other limestones, so far as known, are non-fossiliferous.* The 

 collections were examined by Professor Angelo Heilprin, who gave a list 

 of about twenty species. Comparison of these forms with those obtained 

 in southwestern Pennsylvania and the adjacent portion of West Virginia 

 leads to no positive conclusion respecting the place of the limestone. 

 Three forms, Eumicrotis hawni. Monopteria gibbosa, and Chonetes mille- 

 punctata, have not been reported from any other locality in the Appa- 

 lachian basin. The other forms are widely distributed, most of them 

 having been found below the Mahoning interval. Somewhat similar 

 grouping of forms occurs in a black shale near Dundee, which Mr Hill 

 places about 250 feet above the Mill Creek limestone. As far as the 

 testimony of these fossils is concerned, the Mill creek is as likely to be 

 Allegheny as Conemaugh ; but the coal-making period seemed to have 

 ceased in great measure after the Hillman bed, so that here one finds 

 conditions characterizing the Conemaugh in the bituminous areas. 



It seems altogether probable that the higher beds of the Northern 

 fields are wholly unrepresented in the Southern field. In an earlier part 

 of this work it was seen that the Pottsville diminishes northwestwardly, 

 so that the vast pile of the Southern is represented by a very short col- 

 umn in the Northern field. In the higher measures one finds that the in- 

 terval, Buck Mountain to Tracy, diminishes almost to one-half in passing 

 from the neighborhood of Pottsville into the western Middle. If the 

 change continue in this upper portion as in the Pottsville, the great 

 column of the Southern field should be represented by less than the lower 

 half of the column in the Northern field; so that one might regard the 

 rocks above the Hillman coal bed as without equivalent in the Southern 

 field. 



* Annual Report for 1885, pp. 449 et seq. 



