174 Frank Carney 



Pennsylvanian rocks of Ohio. Formerly the term Carbonifer- 

 ous was applied to both these rocks and the formations now in- 

 cluded in the Mississippian period. As students learned more 

 about this entire series, it became evident that the conditions 

 under which the lower members were deposited differed much 

 from later conditions. For this reason, the early part of the Car- 

 boniferous was set off into a separate period, the Mississippian, 

 and the upper part was named the Pennsylvanian. 



About ten thousand square miles of the state's surface is covered 

 by the Pennsylvanian formations. The entire thickness of this 

 series approximates 1600 feet. In the lower part, conglomerates 

 and sandstones are more common. Above these, the sandstone 

 becomes more shaly, occasionally consisting entirely of shale. 

 Throughout the whole series, limestone beds are irregularly dis- 

 tributed; they are seldom very thick, usually less than a foot. 

 Elsewhere calcareous shales and sandstone appear. Scattered 

 through the Pennsylvanian rocks, are found twelve to fifteen 

 seams of coal. Four or five of these are of slight importance, 

 being ver}^ thin, and containing so much clastic material that 

 they have no value as fuels. 



While the Pennsylvanian formations appear over so wide a sur- 

 face of the state and have a considerable vertical thickness, it 

 does not follow that the given beds themselves have a corre- 

 sponding horizontal area. These sediments were laid down in 

 shallow basins, bordering the sea, and some distance inland. 

 The arms of the sea gradually contracted, thus giving the sedi- 

 ments a shingled attitude. Sixteen hundred feet, which is the 

 estimated thickness of the several beds outcropping one above the 

 other, does not mean that difference in the altitude of the youngest 

 and oldest rocks of the series. 



Methods of mining. In the early days, the outcrops of coal 

 along the hill slopes attracted attention. These exposures wei*e 

 worked by drift mining, and since, in Ohio, the coal beds have 

 been deformed but little, these shafts did not var}^ much from the 

 horizontal. The usual dip of coal beds is from twenty-five feet to 

 thirty feet per mile. Later, vertical shafts were used. So far as 

 recorded, the first shaft of this kind was erected at Steubenville 

 in 1856.23 



-^ Geological Survey of Ohio, vol. v, (1SS4), p. 323. 



