DIFFERENT PROVINCES OF NORTH AMERICA IN LATE PALEOZOIC TIME 67 



"'THE CONEMACGH SERIES. 



'"As now limited, it includes all of the strata from the floor of the Pittsburgh 

 coal down to the top of the Upper Freeport bed, the whole having an average 

 thickness of 600 feet, though it varies from 400 on the western margin of the 

 Appalachian field in Ohio to 800 feet near Charleston, West Virginia. 



'"The series as thus limited above and below, consists of two widely different 

 members, lithologically considered, the upper composed largely of soft, red, and 

 marly shale, the lower of massive, pebbly sandstones. The difference in the 

 rock type is so marked, and especially in the character of the topography made 

 by each, that the First Geological Survey of Pennsylvania and Virginia placed 

 them in two different series, the massive sandstones, at the base of the Conemaugh, 

 being classed with the underlying Allegheny. That assignment, based primarily 

 upon difference of rock type, was more philosophical than the present limitations, 

 but the fact that no definite boundary (a sandstone always being subject to 

 sudden and rapid change in both thickness and character) could be assigned to 

 either the lower limits of the upper one, or the upper limits of the lower one, led 

 Professors Stevenson, Lesley, and other Pennsylvania geologists to extend the 

 limits of the "Lower Barren Measures" of Rogers down to the horizon of the 

 Upper Freeport Coal, a well-marked and widely persistent stratum. This 

 arrangement gives definiteness to classification, a great desideratum, but it has 

 the fault of bringing together rocks of very different type, and hence, while 

 apparently preferable to the old and indefinite dividing-line between the two 

 series, is yet not altogether satisfactory. Hence, it is possible that a future and 

 more detailed study of the series in West Virginia may reveal some more desirable 

 dividing-plane between the Conemaugh series and the underlying Allegheny than 

 the present one (Upper Freeport Coal) , which will retain all of the desirable features 

 of the Rogers classification and at the same time relieve it of indefiniteness. 



'"Viewed from the standpoint of change in physical conditions, the proper 

 place for such a dividing-plane between the Conemaugh series and the Allegheny 

 beds would be the first general appearance of red rocks, near the horizon of the 

 Bakerstown coal about 100 feet under the Ames or crinoidal limestone horizon. 

 That a great physical change took place soon after the deposition of the Mahoning 

 sandstone rocks, the present basal members of the Conemaugh series, must be 

 conceded, since no red beds whatever are found from the base of the Pottsville 

 up to the top of the Allegheny, and none worth considering until after the epoch 

 of the Upper Mahoning sandstone. 



"'The sudden appearance or disappearance of red sediments after their 

 absence from a great thickness of strata is always accompanied by a great change 

 in life forms, and the present one is no exception. In fact, the invasion of red 

 sediments succeeding the Mahoning Sandstone epoch of the Conemaugh may 

 well be considered as the "beginning of the end" of the true Coal Measures, 

 both from a lithological as well as a biological standpoint, and hence it is possible 

 that the best classification aside from the conveniences of the geologist, would 

 leave the Mahoning sandstone in the Coal Measures and place the rest of the 

 Conemaugh, as well as the Monongahela series above, in the Permo-Carboniferous. 

 This reference is also confirmed by the character of the fauna and flora, both of 

 which contain many forms that characterize the Permo-Carboniferous beds of 

 Kansas and the West, as may be seen in the lists published on a subsequent page 

 under the detailed description of the principal Conemaugh strata, 



"'As already stated, the two types of rock (hard and soft) included in this 



