COAL FIELDS. 271 



Carboniferous System. 



Upper Barren Measures. 

 Upper Coal Measures. 

 Lower Barren Measures. 

 Lower Coal Measures. 

 Serai Conglomerate. 



It is the lowest of these divisions, for the establishment of which 

 we find no suitable justification in the facts as they occur in Ohio, con- 

 sidered by themselves alone. With us, this part of the scale would cer- 

 tainly be merged in the next higher division, viz., the Lower Coal Meas- 

 ures, if we were to consult our own geology solely. It has, in fact, al- 

 ways been so treated, in the discussion of our series in the state reports. 

 But this treatment isolates our coal field and breaks up a scientific ar- 

 rangement that has a wide spread application and ought to be abandoned. 



These several divisions will be considered separately. 



SECTION I. 



The Coal Seams of the Conglomerate Coal Measures. 



( Serai Conglomerate, Pottsville Conglomerate, No. XII.) 



This series was originally described as an enormous mass of con- 

 glomerate, mainly white, interbedded with gray sandstones, with a maxi- 

 mum thickness of eleven hundred feet in the Pottsville coal field of 

 eastern Pennsylvania. It was noted at an early date however, that sev- 

 eral coal seams were found, included in the conglomerate. As the formation 

 is followed westward, across Pennsylvania, as has been fully demonstrated 

 by the Second Geological Survey, it is reduced in volume and its con- 

 glomeritic features are less pronounced and sometimes wholly lost, and 

 certain intercalated elements acquire greater development and impor- 

 tance. When the series was at last traced into Ohio in Trumbull and 

 Mahoning counties, the pebble rock, though present in a thin stratum 

 was no longer its most striking feature, but it was found to consist of 

 coal seams, fire clays, limestones, iron ores, shales and ordinary sand- 

 stones. In other words, it had become a considerable and integral part 

 of our productive coal measures. The conglomerates are, however, still 

 recognizable, and while we should never have thought of making them 

 the normal and characteristic elements of the section, we are still able to 

 recognize all the divisions of the Pennsylvania system within our limits. 

 There are three main divisions of the Serai Conglomerate, in western 

 Pennsylvania, viz., the Homewood sandstone, the Conoquenessing sand- 

 stones, upper and lower, and the Sharon conglomerate. The Sharon 

 conglomerate is fairly well developed in northeastern Ohio. The Cono- 

 quenessing sandstones are also in some localities, well represented. They 

 are known by us as the Massillon sandstone, while the Homewood sand- 

 stone is much reduced in thickness, supports no quarries and has conse- 



