CORRELATION 589 



port have been connected by numerous intermediate sections by many 

 independent investigators. 



The strata of the Georges Creek basin are also continuous with those 

 of the Upper Potomac basin. The distance from the latter basin to the 

 Upper Youghiogheny basin is 8 miles; from the Upper Youghiogheny 

 basin to the Preston County section 15 miles; from the Preston County 

 section to Morgantown 18 miles. The section at Morgantown is again 

 connected with the typical areas in Pennsylvania by sections studied 

 by many independent workers. 



The facts adduced show that the correlation of the series is manifest. 

 Two conclusions follow: 



1. There is a persistent eastward thickening of the Conemaugh, the 

 formation being 350 feet thick in southeastern Ohio, 600 feet at Pitts- 

 burgh, and 900 feet in the Georges Creek Valley of Maryland. The 

 failure to recognize this eastward thickening has led, in the past, to the 

 assig-nment of the same thickness to the Conemaugh formation in Mary- 

 land as at Pittsburgh, with the consequence that a considerable part 

 of the Conemaugh formation has been assigned to the Allegheny forma- 

 tion by former workers in Marjdand. 



2. The Davis coal of Maryland and adjacent parts of West Virginia 

 is in the position of the Upper Freeport coal. 



CORRELATION OF FORMATIONS 



In general. — We have now traced a series of strata through the CoaJ 

 Measures of the northern Appalachian basin which serves as a datum 

 plane to which the other beds may be referred. We thus have a key 

 to the correlation of the middle Coal Measures of the northern Appala- 

 chian basin. The correlation of the Monongahela will be briefly sug- 

 gested, after which the relations of the underlying formations will be 

 considered more fully. 



Monongahela formation. — The upper limit of the Monongahela forma- 

 tion of Maryland has been placed, in the past, at the top of a thick coal 

 situated 250 feet above the Pittsburgh seam, which has been called the 

 Waynesburg coal. The latter coal is preserved in but a small area and 

 its true relations need further investigation. The base of the Monon- 

 gahela formation is clearly marked by the thick Pittsburgh coal, which 

 is recognizable throughout most of the area by its character and strati - 

 graphic relations. It furnishes an important datum plane for correla- 

 tion in the northern Appalachian basin. 



