222 CLARK AND MARTIN THE COAL MEASURES OF MARYLAND 



Middle Kittanning coal (18). — Another seam of equal persistence is 

 found at a distance of from a few inches to 30 feet above the top of the 

 Lower Kittanning coal. Over broad areas it is so close to the Lower 

 Kittanning that the two form practically one seam. The upper of these 

 closely associated seams is probably the equivalent of the Middle 

 Kittanning coal of Pennsylvania. 



The Lower and Upper Kittanning coals are called in the upper Poto- 

 mac basin the Davis coal, and locally in the lower Georges Creek basin 

 and in the vicinity of Piedmont, West Virginia, by the name of the " Six- 

 foot." 



Upper Kittanning coal (19). — Separated from the Middle Kittanning 

 coal by from 30 to 60 feet of shale and sandstone is a seam of coal from 

 1 to 3i feet in thickness. This is in the position of the Upper Kittan- 

 ning coal. 



Lower Freeport sandstone (20). — A short distance above the Upper Kit- 

 tanning coal is a massive sandstone of variable thickness, which corre- 

 sponds in position to the Lower Freeport sandstone. 



Lower Freeport limestone (21). — A limestone 16 feet in thickness was 

 encountered at a distance of 28 feet above the Upper Kittanning coal in 

 one of the bore-holes at Henry. This is the horizon of the Lower Free- 

 port limestone of Pennsylvania. This limestone has not been seen 

 elsewhere in Maryland. 



Lower Freeport coal (22). — A seam of coal of variable thickness some- 

 times appears at a distance of from 35 to 60 feet below the top of the 

 Allegheny formation. It corresponds in position to the Lower Freeport 

 coal of Pennsylvania. 



Upper Freeport sandstone (23). — A short distance above the Lower 

 Freeport coal is a very massive, sometimes conglomeritic, sandstone. 

 This is the Upper Freeport sandstone of Pennsylvania. 



Upper Freeport limestone and Bolivar fire-clay (24). — Immediately above 

 the Upper Freeport sandstone, or the horizon of that sandstone, there 

 sometimes appears a thin limestone which corresponds in position with 

 the Upper Freeport limestone. At several places a flint fire-clay has 

 been observed at this horizon, and in such cases the limestone is absent. 

 A similar relationship has been reported from. Pennsylvania, where the 

 Bolivar fire-clay is regarded as " replacing " the Lower Freeport lime- 

 stone. 



Upper Freeport coal (25). — At the top of the Allegheny formation is a 

 very persistent seam of coal, which, in its relationships to the overlying 

 and underlying strata, corresponds to the Upper Freeport coal of Penn- 

 sylvania. This seam has been called the " Four-foot " in the Georges 

 Creek valley and the " Three-foot " in the Potomac valley. In the Pied- 



