CORRELATION 



581 



Coal. 



Meyersdale red beds. 



Buffalo sandstone. 



. ^ (Upper division. 



Brush Creek limestone and faunajj^^^^^ ^.,,.^.^„ 



Brush Creek coal. 

 Bottom. 



Thickness. — The interval between the Harlem and the Brush Creek 

 coal varies from 145 feet in Ohio to 260 feet in Pennsylvania and 

 Maryland. 



Underlying beds. — Another persistent series of beds is found below 

 the Brush Creek coal, which may be recognized by its relation to the 

 overlying strata throughout a large area in the northern Appalachian^;. 

 It includes the following members, which follow immediately beneath 

 the Brush Creek coal: 



Top. 



Irondale limestone. 



Sandstone. 



Thornton fireclay, upper bench. 



Mahoning red beds. 



Coal (local). 



Thornton fireclay, lower bench. 



Mahoning sandstone (massive). 



Coal (local). 



Upper Freeport coal — top of Allegheny formation. 



Upper Freeport limestone. 

 Bottom. 



The relations of these beds will be discussed later. 



Sections of critical series of the Lower Conemaugh from Ohio to 

 Pittsburgh, Pennsylvanm. — These beds furnish a series of datum planes 

 to which the other strata of the Coal Measures may be referred. We 

 will now proceed to trace them in a series of sections from Ohio to Mary- 

 land, beginning on the west in Meigs Count}^, Ohio, and passing thence 

 eastward to the Georges Creek basin of Maryland. In this manner a 

 basis will be laid for the correlation of the middle Coal Measures of the 

 area under consideration. For convenience of description the sections 

 will be grouped in three sets, comprising (1) sections from Ohio to 

 Pittsburgh, (2) those between Pittsburgh and Maryland via West Vir- 

 ginia, (3) those between Pittsburgh and Maryland via western Penn- 

 sylvania. 



Meigs County, Ohio. This area is near the southwestern extremity of 



