310 



OUR COMMON BRITISH FOSSILS. 



ance, being crowded with fossil, corals, shells, etc. ; 

 and not unfrequently we see a white, vertebrate- 

 looking organism cut through — this will doubtless 

 be an Orthoceras. 



In the Carboniferous limestone this family attains 

 its maximum development, for no fewer than one 

 hundred and sixty-nine species have been described 



from this and associated de- 

 posits, up to and including 

 the Millstone Grit. In this 

 list we find fifty-nine species 

 of Goniatites, forty-eight of 

 Orthoceras^ thirty-six of 

 NatitiluSy and seventeen of 

 Discites (which is usually re- 

 garded as a sub-genus of 

 Nautilus), Some of the in- 

 dividuals attain a gigantic 

 size. I have found fossil 

 Nautili in Derbyshire and the Isle of Man which 

 required a strong man easily to lift them. And, 

 especially in the Irish Carboniferous limestone, speci- 

 mens of Orthoceras are met with as thick as a man's 

 thigh. 



Perhaps the commonest of the Carboniferous 

 limestone Goniatites is G. sphcericus. It abounds at 

 Castleton, in the Peak of Derbyshire — at places in 

 swarms. Higher up the series, in the Yoredale shales 

 at Todmorden and Hebden Bridge, there are thin 



Fig. 308.— Beaked Ammonite. 



