NORTH STAFFORDSHIRE COAL FOSSILS. 191 



large scales, probably of Ctenodi, and numerous specimens 

 of Discina, a true marine fossil. The second bed is the 

 shale which occurs above a thin coal called the Bay coal, 

 which was passed through a few years ago in sinking a 

 shaft to the Ash coal. This bed contains many species of 

 fossils of a marine type, some of which are found in the 

 Carboniferous Limestone, while others are restricted to the 

 coal-measures. They include two species of Lingula, one of 

 Discina, together with Productus, Spirifer, Goniatites, and 

 a species of Pala3oniscus, which is also found in the shale 

 of the Stinking coal. 



The alternation of marine with beds of fresh-water origin 

 leads us to enquire how these changes were produced. The 

 solution of this problem is difficult. Nevertheless, it is one 

 of great interest, inasmuch as a true solution of the question 

 would help us to understand much that at present is 

 enshrouded in mystery respecting the origin of coal. At 

 present we are acquainted with at least four beds repre- 

 senting as many changes which took place during the 

 deposition of these coal-measures. Not only was this coal- 

 field subjected to these alternations, but similar changes 

 were in operation during the formation of other coalfields. 

 Mr. Prestwich, in his valuable paper on " The Geology of 

 Coalbrook Dale,"* records the alternation of marine with 

 beds of fresh-water origin in the coal-measures of that 

 district. He accounts for their presence by supposing that 

 they were produced by the oscillation of the land, whereby it 

 was at one time submerged and covered with a stratum of 

 silt containing marine exuvias, and at another raised and 

 converted into a marshy tract, overspread with a thick 

 luxuriant vegetation, and harbouring in its shallow waters 

 numerous fresh-water shells to be again submerged and 



* Trans. Geol. Soc., 2nd Series, vol. v. 



