CORRELATION 587 



Ames limestone and fauna, Harlem coal, Ewing limestone, Fitlshuryli. 

 red beds, Saltshurg sandstone (massive), coal, Albright limestone, Cam- 

 bridge [Friendsville] shale and fauna, coal, Meyersdale red beds, Buffaio 

 sandstone. Brush Greek limestone and fauna. Brush Creek coal. 



The interval from the Harlem to the Brush Creek coal is 260 feet, as 

 compared with 261 feet in a diamond-drill record near Somerset, Penn- 

 sylvania. The section between the Brush Creek coal and the Upper 

 Freeport coal is also in close agreement in the two basins, the interval 

 between them being 115 feet in the Castleman basin and 130 feet at 

 Somerset, Pennsylvania. The agreement of this section with that last 

 described is so close in lithology, in position of faunas, sequence, and 

 intervals and the distance between them (10 miles) is so small that 

 there can be little doubt of their correlation.^^ 



Georges Creek basin, Maryland. This basin lies 10 miles east of the 

 Castleman basin, from which it is separated by the Oakland anticline. 

 The section here exposed includes : 



Ames limestone and fauna, upper and lower divisions; Harlem coal, 

 Ewing limestone, Pittsburgh red shale, Saltsburg sandstone — massive; 

 coal, Albright limestone, Cambridge [Friendsville] shale and fauna, 

 coal, Meyersdale red shale, Buffalo sandstone. Brush Creek limestone 

 and fauna. Brush Creek coal. 



The average thickness is 257 feet. The interval from the Brush Creeji: 

 coal to the Upper Freeport [Davis] coal is 120 feet. 



As will be seen by a comparison of the columnar sections, the agree- 

 ment of this section with that in the Castleman basin is so complete, 

 embracing the same units and faunas in the same sequence, at essentially 

 the same intervals, that their identity is manifest. 



The Georges Creek and the Upper Potomac areas are part of the 

 same structural basin, their strata are continuous, and the sections are 

 in full agreement. We are thus brought to the same conclusion, whether 

 we approach Maryland by way of West Virginia or via western Penn- 

 sylvania. 



Persistence of critical series. — We have now described the critical 

 series of the lower Conemaugh and found that it constitutes a clearly 

 recognizable group, which may be traced throughout the area considered 

 by means of its faunas, lithology, intervals, and sequence. 



The Ames fauna is distinguished throughout the entire area, when 

 normally developed, by its profusion of Ambocoelia planoconvexa, 

 Chonetes granuUfer, typical form, and Derbya crassa. This fauna is 



-^ See columnar sections. 



