522 STEVENSON— THE FORMATION OF COAL BEDS. [N'ov. i, 



ditions. At the same time, it does appear strange that, if the older 

 forms preferred clear water, they are found so seldom in the Mercer 

 and Vanport limestones, formed in long estuaries, while they are 

 so abundant in the muds which are associated with the Brush Creek 

 and in those underlying the Ames. 



It would appear that the distribution and the habits of inverte- 

 brate animals forms lend no support to the belief that the Appa- 

 lachian basin, during Coal Measures time, was ever covered in whole 

 or in part by deep water. The passage of muddy-water-loving 

 pelecypods and gastropods into the more calcareous and even into 

 the limestone areas, the occurrence of such forms in shale patches, 

 lying within limestone areas with different but interlocking fauna, 

 suggest that in the areas of limestone deposit also the water was shal- 

 low, that those were merely estuaries, bordered in great part by 

 lowland areas with very sluggisTi drainage. 



Cornet,^^- in discussing the lowest Coal Measures deposits near 

 Mons in Belgium, regards the absence of gastropods, the abundance 

 of pelecypods with byssus, especially of mytiloids, aviculoids and 

 pectenoids, as evidence that the deposit was littoral. Modern condi- 

 tions on the Belgian coast strengthen his conviction. The abundance 

 of ammonoids might indicate deep water, but this cannot be decisive 

 in the presence of contrary evidence. One can easily understand 

 the presence of cephalopods in littoral deposits, but it would be diffi- 

 cult if not impossible to explain the great abundance of molluscs 

 with byssus in deposits made far off shore. He says that Barrois 

 had come to the same conclusion respecting the alum-bearing shales 

 at Marly, but E. Haug has p^laced generally among deep sea deposits 

 the shales and fine shaly sandstones with Goniatitcs and Pscudo- 

 nomya, constituting the Culm. While the life indicates littoral 

 deposition, the fine grain of the H la sediment seems to accord better 

 with a certain distance from the shore. But this objection means 

 nothing for, as actual conditions show, the coarseness or fineness of 

 shore deposits depends on features of the area, its lithology, altitude 

 and climate. The coal terrain, excepting intercalations only a few 



112 



'J. Cornet, '' Le terrain houiller sans houille (H la) et sa fauna dans 

 le bassin du couchant de Mons," Ann. Soc. Geol. de Belgique, Vol. XXXIV., 

 1906, Mem., pp. 139-152. 



