18 GEOLOGY OF OHIO. 



are much finer and more impervious than in Pennsylvania, and are with- 

 out the layers of sandstone and conglomerate which, on Oil Creek, serve 

 as reservoirs for the oil, and also that the rocks of Pennsylvania are more 

 disturbed than those of Ohio. This latter statement is denied by Prof. 

 Lesley in his note to the report of Mr. F. A. Randall, On the Geology of the 

 Vicinity of Warren, where he says : "The district of greatest oil produc- 

 tion of Pennsylvania is precisely the district where there has never been 

 any disturbance whatever. =i= * * In fact, had not "Western Pennsyl- 

 vania been lifted from the ocean bed into the air at the end of the coal 

 era in a steady and gentle manner,' without disturbance, the oil production 

 would never have been a historical event." Such a statement, coming 

 from such a source, is not a little surprising, for every geologist knows 

 that the great disturbance which formed the folds of the Alleghany 

 Mountains was felt throughout Western Pennsylvania, and we have con. 

 clusively proved that its influence extended even into Ohio. The series 

 of basins which the Coal Measures exhibit in and immediately east of 

 the oil region, are indisputable records of just such disturbance of their 

 original horizontality as are indicated in the remarks referred to. That 

 these disturbances were slight compared with those that affected the cen- 

 tral portion of the Allegheny belt is evident ; that they were suflScient 

 to fracture and loosen rigid sandstones will hardly be denied by any one 

 who knows any thing of the structure of the country under consideration 

 and the condition in which the " oil sands " that underlie it are found. 



The experience of all the well-borers has shown that these are cracked 

 and fissured in every_ direction, and their capacity as reservoirs is thereby 

 greatly increased. As they were once unbroken sheets of sand and gravel 

 their present shattered condition must have resulted from mechanical 

 violence. That no disturbance could occur in the oil region without 

 breaking up the strata and permitting the oil to escape, is a gratuitous 

 and groundless assumption, for it is well known that a disturbance which 

 would fracture and open the rigid sandstones, might leave the plastic 

 clay shales still impervious. 



CARBONIFEROUS SYSTEM. 



THE EEIE SHALE. 



As stated in th^ description of this formation contained in our first 

 volume — the name Erie shale was applied to the great mass of argilla- 

 ceous shale which forms the shore of Lake Brie from the Pennsylvania 

 line to Avon Point. This was shown by the investigations made in the 

 first year of the existence of the Geological Survey to be the western ex- 



