GEOLOGICAL scale AND STRUCTURE. 41 



of deep wells, and consequently the facts will be scanty and cannot be 

 worked out minutely, or with absolute certainty. 



The movements to which the Cincinnati axis is due, were in reality 

 profound and long continued, and their influence on the geology of this 

 portion of the Mississippi, were far-reaching. All the dips of the strata 

 in the southwestern quarter of the state stand in close connection with 

 the formation, and growth of the Cincinnati axis. These dips are mainly 

 southeasterly in direction and are satisfactorily accounted for by the uniform 

 growth of the Cincinnati axis while the strata were in progress of formation. 

 So far as known the Cincinnati anticline is nowhere, in southern Ohio or in 

 the states of Kentucky and Tennessee, distinctly .associated with the ac- 

 cumulation of petroleum ; but in central and northern Ohio and also in 

 Indiana, its influence in this connection has lately been found to be im- 

 portant and of vast economic interest. A slight modification may be re- 

 quired as to the date of the origin of this great feature in the latter areas. 

 The Indiana gas field, which is probably the largest continuous gas field 

 thus far discovered in the world, is wholly conditioned by and dependent 

 on the broad up-lift which is the immediate and direct extension of the 

 Cincinnati axis. It is certain, however, that the movements of the strata 

 in the territory last named, by which petroliferous accumulation was pro- 

 vided for, occurred at a much later' date than that assigned for the original 

 emergence of the Cincinnati axis at the southward. Upper Silurian and 

 Devonian strata are distinctly involved in the low arch in which the gas 

 and oil are gathered. The same thing is true of the broken structure on 

 which the oil production of Hancock and Wood counties in northern 

 Ohio, depends. This district can be referred to the Cincinnati arch 

 only by a very liberal interpretation of this great structural feature of the 

 state. The details of this structure are traced out at some length in 

 Geology of Ohio, Volume VI, chapter III. 



The Appalachian Folds of Eastern Ohio. 



The rock flexures of eastern Ohio are invested with much more 

 general interest than the facts pertaining to the far more ancient and ob- 

 scure Cincinnati uplift. The cause of this greater interest is found in 

 the economic importance of the former in connection with oil and gas. 

 The anticlines of eastern Ohio are unmistakably part and parcel of the 

 great series to which the Allegheny mountains of Pennsylvania and Vir- 

 ginia belong. These folds are exceedingly well developed in central 

 Pennsylvania. The whole system of Paleozoic rocks ' is there bent into 

 enormous arches in which two or three miles of length are compressed 

 into a single mile. Nowhere in the world is there any more striking and 

 beautiful exposure of rock arches than here. The number of distinct 

 folds is considerable ; but as the series is followed to the westward the 



