MONONGAHELA FORMATION 229 



as the Sewickley coal, in being traced westward from its type locality 

 by the Pennsylvania geologists, has been found to split into two seams, 

 it is considered probable that the same has taken place to the eastward. 

 This seam is therefore referred to the Lower Sewickley. 



Upper Sewickley or Tyson coal (50). — A seam of coal of great persistence 

 and considerable economic importance is found at an interval of about 

 45 feet above the Lower Sewickley, and from 105 to 120 feet above the 

 Pittsburg coal. This seam has long been known in the Georges Creek 

 region as the Tyson or " Gas " coal. As is stated above, this seam falls 

 within the position of the Sewickley coal, and probably corresponds to 

 the upper split of the Sewickley in western Pennsylvania and eastern 

 Ohio. 



Sewickley sandstone (51). — Separated from the underlying Upper Sewick- 

 ley coal by a variable thickness of shale is a sandstone whose greatest 

 observed thickness in Maryland is about 15 feet. Dr I. C. White, in 

 Bulletin No. 65 of the United States Geological Survey, calls attention 

 to the fact that either a limestone or a sandstone, one only, however, 

 to the exclusion of the other, occurs in the interval between the Sewick- 

 ley and the Uniontown coals. Where sandstone occurs in this interval 

 it is called the Sewickley sandstone. The limestone, on the other hand, 

 has been differentiated into the Uniontown and " Great " limestones. 

 Throughout Maryland the limestone is apparently entirely absent. This 

 occurrence therefore confirms the generalization which Doctor White 

 based on his observations in Pennsylvania, West Virginia, and Ohio, 

 namely, that either the limestone or the sandstone, but never both, are 

 found in the interval between the Sewickley and Uniontown coals. 



Uniontown coal (52). — A thin coal is found in the pumping shaft section 

 near Frostburg, about 60 feet above the Upper Sewickley coal and close 

 to the top of the Sewickley sandstone. It corresponds in position and 

 character to the Uniontown coal of Pennsylvania. 



Uniontown sandstone (53). — A short distance above the Uniontown coal, 

 in the Pumping Shaft section, there is a thin sandstone which is proba- 

 bly a poor representation of the Uniontown sandstone. 



Waynesburg limestone (54). — A limestone occurs a short distance above 

 the Uniontown sandstone and from 20 to 30 feet below the top of the 

 formation which corresponds in its stratigraphic position to the Waynes- 

 burg limestone of Pennsylvania and West Virginia. 



Waynesburg coal (55). — There is a very persistent coal seam, of con- 

 siderable economic importance, that may occur anywhere in the interval 

 up to 20 feet above the top of the Waynesburg limestone. From its 

 position, 230 to 250 feet above the base of the Monongahela formation, 



