830 FLORAL ZONES OF THE POTTSVILLE FORMATION. 



Pennsylvania — and tho terranes extending from coal A to at least as 

 far as coal C in the Northern Anthracite iield, were laid down prior 

 to the deposition of the roof shales of the Twin coal. 



The examination of the plants from the above-mentioned basal beds 

 of the Allegheny series shows that they constitnte a typical Coal Meas- 

 ures flora, with but a small proportion of Potts ville forms, though the}' 

 lack so high a development of the Pecopteroid group, as well as several 

 other more advanced types which appear in the Kittanning and Buck 

 Mountain coals. The same is true of the flora of coal C in the North- 

 ern Anthracite field. In fact, like the flora of coal A at Tamaqua, or 

 like that indicated in the coal 72 feet below the Twin bed in the Potts- 

 ville Gap, and that of the lower horizons of the measures in the North- 

 ern Anthracite field, the floras of the basal beds of the Allegheny series, 

 which are above the lithologic Pottsville in the bituminous basins, are 

 clearly referable, on paleontologic grounds, to the Lower Coal Meas- 

 ures. In short, the comparative paleontology of the terranes shows 

 {<() that, as related to the Coal ]Measures of other regions of the Appa- 

 lachian province, or other basins of the world, the flora of the roof 

 of the Twin coal, which has been made the dividing line between the 

 Pottsville formation and the Lower Coal Measures in the Southern 

 Anthracite field, is of a pure and well-advanced Coal Measures type; 

 and (/>•) that its horizon is distincth' above beds, generally of no great 

 thickness in the northern basins, containing floras characteristic of not 

 so high a level, but nevertheless having a composition which is distinct 

 from that of the floras of the Pottsville formation and which is too 

 thoroughly identical with the plant life of the Lower Coal Measures to 

 permit of any other reference. 



From the foregoing it appears: First, that the conventional upper 

 limit of the Pottsville formation, in the Southern Anthracite field, is 

 higher than the paleontologic upper limit. Second, that its horizon is 

 also considerablv above that of the same boundary as drawn., not only 

 in the ])ituminous basins, but also in the Northera Anthracite fields. 

 Third, that the paleontologic limit appears, so far as evidence has been 

 ol)tained, to lie below, though perhaps very near to, the coal at 72 

 feet below the Twin coal in the type section, and probably above 

 the plant beds 210 feet below the Twin coal. In other words, it also 

 appears that in the type section the paleontologic upper limit of the 

 Pottsville formation lies close within the upper outskirts of the great 

 plexus of conglomerates in which the formation culminates. Thus, the 

 paleontologic limit falls within and near the natural or lithologic limit. 



It hardly need be repeated that the A coal at Tamaqua should, 

 according to the evidence of the fossil plants, ])c included in the Lo win- 

 Coal Measures, as should, also, the thin bed next below the Twin 

 coal in the type section. It is not impossible that one or the other of 

 these lower coals is the representative of the Scott Steel coal occurring 



