16 Proceedings of the Royal Physical Society. 



Carboniferous Limestone group of the niidland counties of 

 England was laid down. The fauna was on the whole 

 estuarine, though occasional fresh-water and land animals 

 are met with. Marine forms resembling those in the 

 Carboniferous Limestone occur in thin bands on several 

 horizons throughout the group. These organisms, especially 

 the brachiopods, though in places met with in large numbers, 

 are confined to one or two species in each band, while the 

 individuals are stunted and dwarfed as if they had lived in 

 an uncongenial habitat. In the border territory, however, 

 the marine fossils in some of these beds are as well developed 

 and the species are as varied as those of the Carboniferous 

 Limestone of central Scotland. This resemblance need not 

 be wondered at, since the alternation of conditions must have 

 been precisely the same. 



In the different areas there is a strong similarity between 

 the marine and estuarine forms of the invertebrata, the 

 species being nearly identical. But the higher Crustacea 

 and the fishes, especially the ganoids, though closely allied, 

 yet differ specifically — a distinction which may be accounted 

 for on the supposition that they lived in different estuaries 

 on opposite sides of the Silurian barrier. In the western 

 area there are few marine forms present, the fossils being 

 chiefly ostracods, but when marine organisms occur they 

 resemble those in the other areas. 



The flora met with in the Cement-stone group, the Car- 

 boniferous Limestone, and in the Millstone Grit is identical 

 with the Culm flora of the Continent. The plants, however, 

 are not of much service in determining the existence of these 

 barriers in Lower Carboniferous time, because they would 

 readily migrate from the one side of the land barrier to the 

 other, and would not therefore undergo much modification. 



The doctrine of colonies so obviously taught by the Car- 

 boniferous Limestone formation of Scotland deserves a pass- 

 ing reference. The members of this series, which probably 

 represent part of the Yoredale rocks of England, show that 

 by the time of their deposition the barriers had shrunk in 

 size, if, indeed, they had not altogether disappeared. In 

 marked contrast with the underlying Cement-stone group, 



