138 Frank Carney 



Stratigraphy of oil and gas 105 



Ordovician, Silurian, Devonian 



Mississippian, Pennsjdvanian 



Occurrence in rock 

 Origin of oil and gas 16< 



The inorganic theory 



The organic theorj^ 

 Production of oil and gas 169 



Natural gas 



Petroleum 



Clay 170 



Properties of clay 

 Kinds of clay in Ohio 

 Rank of state 



Coal 173 



Pennsylvanian rocks of Ohio 



Methods of mining 



Centers of coal mining 



Geography of Ohio in the Pennsylvanian period 



The origin of coal 



Kinds of coal 



Rank of state in coal production 



INTRODUCTION 



Agriculture alone can give a commonwealth a high position. 

 But the crop-producing capacity of a soil is in no wise diminished 

 by the fact that mineral wealth may underlie the area. Agri- 

 cultural states, having mineral wealth, are thereby the richer. 

 Earl}^ in its history, Ohio took a foremost position in the pro- 

 duction of minerals. WHiile its rank in reference to particular 

 minerals has shown great change, it still outranks other states 

 in some valuable products. The earliest explorations in Ohio 

 appear not to have had for an object the discovery of minerals. 

 The first settlers came into the state to establish farm homes, 

 and the early exploitation of its minerals was made to satisfy 

 local demands that could not very well be met otherwise. The 

 iron ores were worked at first to supply the needs of households 

 and farms. For this reason the iron mines in Ohio were of great 

 importance during its early decades. 



