CORRELATION 585 



Ames limestone and fauna, Harlem coal, Eiving limestone, Pittshurg'n 

 red beds, Saltshurg sandstone, [Maynadiei-] coal, Albright limestone, 

 Cambridge red beds, [Thomasj coal, Buffalo sandstone, Brush Creek 

 limestone and fauna. Brush Creeh coal. 



The average interval from the Harlem to the Brush Creek coal, as 

 shown by diamond drill-holes, is 218 feet, which is in close agreement 

 with the thickness of 222 feet in the Upper Yonghiogheny basin. Tlie 

 underlying beds, between the Brush Creek and the Upper Freeport lime- 

 stone, are also in agreement in the two basins, including [ Corinth j 

 sandstone, Thornton clay, Mahoning red beds, [Gallitzin] coal, Mahon- 

 ing sandstone, [Piedmont] coal. Upper Freeport [Davis] coal, and thcj 

 Upper Freeport limestone, which are found in both basins. The inter- 

 val from the Brush Creek to the Upper Freeport [Davis] coal is 110 

 feet in the Upper Yonghiogheny basin and 120 feet in the Upper 

 Potomac. 



The Davis coal is thus seen to occupy the position of the Upper Free- 

 port coal. The Piedmont coal above it is perhaps a split from the latter 

 seam. 



The section described is in harmony, in all important members as 

 well as in intervals, with that exposed in the Upper Yonghiogheny 

 basin, as seen by comparing the columnar sections of the two basins 

 (shown in plate of columnar sections). The chief difference observed 

 is the presence of the Cambridge red shale in the Upper Potomac basin 

 and its absence in the Upper Yonghiogheny basin. The identity of the 

 sections, in all important respects, is manifest. 



Sections of critical series of Lower Conemaugh from Fittsburgli to 

 Maryland via western Pennsylvania. — ^We have described the sections 

 between Pittsburgh and Maryland via West Virginia anc^ found the 

 critical series to extend from Ohio to Maryland via West Virginia. We 

 will next consider the sections from Pittsburgh to Maryland via western 

 Pennsylvania. 



Freeport, Pennsylvania. The section of the Lower Conemaugh and 

 Upper Allegheny at Freeport, Pennsylvania, is of particular interest, as 

 this is the typical locality of the upper members of the Allegheny forma- 

 tion and hence determines the boundary between the Conemaugh and 

 Allegheny formations. The following section was observed at this 

 place : ^^ 



Ames limestone and fauna, Pittsburgh red beds, Saltsburg sandsionr. 



^® Section by Swartz and Bassler. See chart of colnmnar sections for measurements 

 of intervals. 



