williams.] Lesley's statistics. 105 



sylvania, and 15 feet at George's Creek, in Maryland. At Pittsburg 

 it is 8 feet thick, and its outcrop 350 feet above water level. 



The Washington bed, also in the Upper Coal Measures, 150 feet 

 above the Pittsburg seam, has a thickness in places of 11 feet, its 

 average being only 3J or 4 feet. 



In the Lower Productive Measures occur the Freeport bed, having 

 an average thickness of U feet, and the Kittanning and Clarion beds. 



The Upper Barren Measures are characterized by the absence of 

 workable coal beds. They contain 17 different limestone beds. The 

 most persistent is the Upper Washington limestone, which has an aver- 

 age thickness of 30 feet. These Measures also contain a number of 

 sandstone strata, varying from 50 to 100 feet in thickness, and situated 

 in the upper part of the series. They are not as persistent as the lime- 

 stones already referred to. The thickness of this series is estimated at 

 about 1,100 feet. 



The Upper Productive Measures are also characterized by the predom- 

 inance of limestone rocks, which form nearly one-fourth of the whole se- 

 ries. There is a great development of sandstones at the top, forming 

 the cliffs along the river at Waynesburg. In this division occurs the 

 Pittsburg coal bed. 



The Pittsburg Barren Measures have an average thickness of GOO 

 feet, and include four beds of massive sandstone : The Counellsville 

 sandstone ; the Morgantown sandstone, which is oil-bearing and 150 

 feet beneath the Pittsburg seam, and 50 feet thick ; the Saltsburg sand- 

 stone; the Mahoning sandstone. 



The limestones occur mainly under the Pittsburg coal seam and 

 above the Connellsville sandstone. Two hundred and fifty feet below 

 the former is the Crinoidal limestone, and 100 feet above the Mahoning 

 sandstone is found the Black limestone. The coal of this division is of 

 no commercial value. 



In the Alleghany series the first geological survey recognized but six 

 divisions, but the second geological survey found it necessary to sub- 

 divide each of the series into three parts. A curious feature of this 

 series is that it contains cannel coal beds. 



But one persistent limestone is recognized in this group, designated 

 as the Ferriferous limestone, which has been used as a key for the loca- 

 tion of the oil-sand deposits beueath. This is followed by the Potts- 

 vine Conglomerate (No. XII), composed chiefly of three massive sand- 

 stone subdivisons, small coal seams, and fossiliferous limestones; next 

 lower is the Mauch Chunk Red shale (No. XI), containing the iron ores 

 of Uniontown and the siliceous limestone so well developed at Blairs- 

 ville and Trough Creek, Huntingdon County, Pennsylvania, and which 

 to the south develops into the great Subcarboniferous limestone. It 

 also appears in Ohio and Kentucky, and in the Mississippi Valley is 

 known as the " Archimedes limestone." 



The Mountain sandstone group (No. X), occurs about 76*0 feet below 



