518 STEVENSON— THE FORMATION OF COAL BEDS, [-^'ov- i. 



shales, but they are of the same species as in the overlying limestone 

 and of equal size. 



The lists, as has been said, are local ; they do not suffice for 

 comparison of faunas at the several horizons ; but that is unimpor- 

 tant here. Each locality has been examined with such care as to 

 give a just conception of the manner in which the several groups of 

 organisms occur. It should be kept in mind that fossiliferous beds 

 are not only fewer in number within the Appalachian Pennsylvanian 

 than in the region west from Cincinnatia, but also very much less 

 prolific in species and less commonly so prodigal in individuals. 

 These features suggest to the paleontologist that marine conditions 

 in the Appalachian basin were abnormal. 



The coelenterates give no information respecting the conditions. 

 Only two species of coral have been found and one of them has no 

 preference for limestone over shale, individuals being equally abun- 

 dant in both. One of the crinoids has a similar distribution. 



Few species of bryozoans have been reported but these abound 

 at several horizons. They are found in pure and impure limestones 

 as well as in shales containing very little calcareous matter. They 

 are characteristic of somewhat sandy shales in the Waverly of north- 

 ern Ohio. Ulrich^^"' says that bryozoans of recent time flourish best 

 in water depositing slightly argillaceous limestone — relatively quiet 

 water — and at depths little beyond the zone of violent wave action. 

 The habits of these animals seem to justify the conclusion that the 

 limestones and other beds in which they abound, the Mercer, Van- 

 port and Cambridge, were deposited in comparatively shallow water, 

 probably less than lOO feet deep ; and this conclusion is strengthened 

 by the fact that in some localities the area of those limestones was 

 so restricted that violent wave action would be hardly possible. 



The brachiopods, at first glance, are less definite. According to 

 Schuchert,"^ among recent species of inarticulated brachiopods 24 

 live between high tide and 90 feet ; 7 between 90 and 600 feet, and 

 only one at great depths. Lingula and Discina are unknown below 

 90 feet but Crania and Discinisca occur at greater depth. The inar- 

 ticulated forms have changed comparatively little in character since 



""E. O. Ulrich, Bull. Geol. Soc. Amer., Vol. 22, 191 1, p. 252. 

 C. Schuchert, Bull. Geol. Soc. Amer., Vol. 22, 191 1, pp. 258-275. 



Ill 



