292 STRATIGRAPHICAL GEOLOGY 



i 



Estheria swarming in some localities. Several species of Xipho- 

 sura allied to the modern Limulus (king-crab) have been described 

 by Dr. Woodward, and referred to the genera Prestwichia and 

 Belinurus. There were also a few Eurypterids, this being their 

 last appearance in England. 



c. Fishes. Fish remains, of Crossopterygian and Elasmobranch 

 genera, are everywhere abundant, but it is difficult to separate 

 entirely the freshwater forms from the marine, because some (like 

 the Mollusca) seem to have been equally at home in salt and brackish 

 water ; some of them, like the modern salmon, may have lived in 

 the sea at certain seasons, and in the estuaries and rivers during 

 other parts of the year. The following genera are, however, most 

 frequently associated with the Coal-measure plants : Ccelacanthus, 

 Cheirodus, Gtenacanthus, Ctenoptychius, Gyracanthus, Megalichthys, 

 Platysomus, Pleuracanthus, Rhizodus, Rhizodopsis, and Strepsodus. 



d. Amphibia. Thirteen genera of Labyrinthodonts are 

 recorded from British Carboniferous rocks, Anthracosaurus, 

 Loxomma, Ophiderpeton, Urocordylus, etc., mostly from the Jarrow 

 coalfield in Leinster, Ireland. Others (Archegosaurus) occur in 

 Prussia and (Baphetes, Dendrerpeton) in Nova Scotia. Footprints 

 have also been observed in the Forest of Dean coalfield and in the 

 limestone series of Dalkeith, Scotland. The larger of these 

 Amphibians are believed to have measured 7 or 8 feet in length, 

 but others were very small ; they were probably fluviatile creatures 

 preying on the fish and Crustacea which swarmed in the swamps 

 and lagoons of the period. 



3. The Marine Fauna 



The Millstone grits are probably marine deposits, for land 

 plants are not common in them, and the intercalated shales some- 

 times contain marine species of Mollusca as well as fish remains. 

 The Lower Coal-measures were swamp deposits formed along the 

 fringe of sinking land areas, parts of which were from time to time 

 invaded by the sea. Hence marine fossils are found in them at 

 certain horizons. The species which have been found in these 

 beds in Britain and also at two horizons in the Middle Coal- 

 measures of Staffordshire are tabulated on p. 293. The first two 

 columns show how many of the species range up from the higher 

 parts of the Avonian Series. 



C. WESTPHALIAN SERIES IN BRITAIN 



Just as the Lower Carboniferous Series is in most places brought 

 to the surface along tracts of anticlinal flexure, so the Upper Series 



