3 io 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 

 Nautilus, and seventeen of 

 Discites (which is usually re- 

 garded as a sub-genus of 

 Nautilus). Some of the in- 

 dividuals attain a gigantic 



Fig. 308. Beaked Ammonite. 



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 



