Carboniferous Limestone Fossils. 129 



also thrown into a series of undulating anticlinal and 

 synclinal curves, great denudations occurred, and the 

 result was that the individual coal-fields now lie in 

 basins often separated from each other by intervening 

 tracts of Millstone Grit and Carboniferous Limestone. 

 Sometimes portions of these basins are concealed by 

 unconformable overlying Permian and New Red strata. 

 Thus, the Northumberland and Durham coal-field is pro- 

 bably a basin, partly out at sea, and the southern edge 

 of which is overlaid by Magnesian Limestone. The 

 Yorkshire and Derbyshire coal-field is in my belief 

 another basin, the eastern half of which must crop up 

 against the Magnesian Limestone, deep under ground, 

 and miles to the east of where it first dips beneath 

 that limestone. The Lancashire and North Wales coal- 

 fields also form parts of another great basin, in places 

 probably 6,000 feet or more beneath the New Red Marl 

 of Cheshire. These statements will be more easily un- 

 derstood by referring to figs. 63, p. 325, and 115, p. 601. 

 In the purely marine strata of the Carboniferous 

 series, of which the Carboniferous Limestone forms the 

 most important part, we find that more than 30 genera 

 and about 100 species of Corals have been named. 

 Among the most common are species of the genera 

 Cyathophyllum, Clisiophyllum, Syringopora, Litho- 

 strotion, and Zaphrentis. Crinoidea are numerous, 

 the most common of which belong to the genera Actin- 

 ocrinus, G'yathocrinus, Platycrinus, Woodocrinus, 

 and Poteriocrinus ; 3 species of Echiniclse also occur. 

 Trilobites are scarce in the Carboniferous rocks, the 

 most characteristic genera being Griffith/idea and Phil- 

 lipsia. Among other Crustacea there are Estheria, 

 Eurypterus, Prestwichia, Belinurus, and Limulus. 

 Polyzoa are common. Brachiopoda are also exceedingly 



