652 HISTORICAL GEOLOGY. 



Barton coal-bed 1' 



Shale 100', Crinoidal limestone 4', shale 30' 134' 



Coal-bed 2' 



Shale and sandstone 35', black limestone 4', shale 60' 99' 



Coal-bed l'-2' 



Shale 30'-50', with Mahoning sandstone (divided sometimes into 

 Upper, Middle, and Lower), with thin layers of shale and lime- 

 stone, and sometimes a thin coal-bed, in all .195^' in Ligonier 

 Valley, varying to 75' and less elsewhere 75'-195^' 



4. Lower Productive Coal-measures^ or Alleghany Eiver Series, W. Fa. 



Freeport Upper coal, E 2'-4' 



Fire clay 2'-6', shale with ore, Freeport Upper limestone, shales, 



sandstone 25'-40' 



Freeport Lower coal, D 2'-7' 



Fire clay l|'-4', Freeport Lower limestone 42'-50' 



Kittanning Upper coal, C^ li'-5' 



Fire clay 2'-4', Johnstown cement-bed, shales 2'-8' 



Coal 0'-2' 



Fire clay 0'-2', shales and slate 30'-40' 



Kittanning Middle coal, C 1 i'-^' 



Fire clay, shales, sandstone 35'-40' 



Kittanning Lower coal, B 3'-7' 



Fire clay 4'-8', sandy shales ~| sometimes r 50'-60' 



Clarion coal, A > Clarion \ l'-2' 



Fire clay 2'-10', shales > sandstone <-20'-30' 



Brookville coal, A 0'-4' 



Fire clay, brick clay O'-IO' 



POTTSVILLE CONGLOMERATE. 



These sections show many alternations of sandstone, limestone, and shale, 

 with the several coal-beds, but without giving the many minor changes. 



Sections from the Anthracite region afford the same alternation of coal- 

 beds with beds of sandstone (or conglomerate) and shale, but without even 

 thin layers of limestone. But the coal-beds and the various rocks reach a 

 much greater thickness, all being on a grander scale in this central part of 

 the Appalachian area. The " Mammoth " coal-bed (numbered E by the 

 Geological Survey) attains a maximum thickness of 50 feet ; and then, above 

 200 to 300 feet of sandstone (or conglomerate) and shale containing two or 

 three thin coal seams, comes the Red Ash Bed (F), 16 to 24 feet; and above 

 another such interval, a third great bed (G), 15 to 16 feet; and so on. But 

 these thicknesses are not constant, the minimum in each of these beds in 

 other localities (mining shafts) being half the above or less. 



The thickness diminishes not only westward, but rapidly also northward. 

 At Carbondale, it is, for the whole Coal-measures, only 300 feet, and for the 

 included coal-beds less than 20 feet. Near Wilkesbarre, the thickness is 

 about 867 feet, with 85 feet of coal-beds, or about one foot of coal to 10 of 

 rock. In the western Middle Anthracite field, the total at Hammond is 1512 

 feet, with 83 of coal-beds. Near Pottsville, in the southern field, the total 



