116 THE LIAS AMMONITES. 



The Cephalopoda Bed — Upper Lias. 

 Zones of Harpoceeas opalinum and LyxocEKAS jueense. 



Ft. in. 



D. A coarse, dark-brown, calcareo-siliceous rock, full of small, dark, flattened grains of 



hydrate of iron. It contains an immense quantity of fossils, but Ammonites and 

 Beletnnites are the dominant forms ; some of the bivalve shells are well preserved ; 

 the matrix adheres to their surfaces with such tenacity that they can seldom be 

 cleaned without injury. The Ammonites and Nautili, for the most part, want the 

 shell. Harpoceras opalinum and Rhynclionella cynocephala lie in the upper part 

 of the bed, and Lytoceras jurense, Harpoceras insigne, Harp, variabile, Harp, 

 striatulum, Belemnites, Nautili, and other Mollusca in the middle part ; the lower 

 part is not so fossiliferous ; this bed measures 4 6 



Zone op Haepoceeas bifeons. 



E. A hard, coarsCj brown mudstone, with hard irregular nodules of a calcareo-siliceous 



sandstone, highly micaceous and ferruginous, and passing downwards into the 



sands 9 



p. Fine, brown and yellowish, micaceous sands, passing into greyish coloured micaceous 

 sands, with inconstant and concretionary bands of highly calcareous sandstone ; 

 nodules of various sizes occur in these bands, which are sometimes fossiliferous, 

 containing chiefly Harpoceras bi/rons in nodules with Belemnites' 150? 



Zone op Haepoceeas seepentinum. 

 G. Blue clay and shale, marked by the outburst of springs and by pools of water on the 



terrace formed by the Upper Lias Clay 80 



Middle Lias. 

 Zone op Amalthecs maegaeitatus. 

 H. Marlstone ; a hard calcareous sandstone, resting on brown and grey sands, with 



bands and nodules of ferruginous sandstone 150 



Zone op Aegoceeas Henleyi. 

 I. The shales of the Middle and Lower Lias, sloping down into the valley. 



13.-^ The Zone of Harpoceras serpentinum. 



Synonyms. — " Alum shale," Young and Bird, ' Geol. of York.,' p. 133, 1832. " Upper 

 Lias," part, of English authors. " Posidonien-Schiefer," Romer, ' Oolit. Geb.,' p. 5, 1 836. 

 " Lias-Schiefer," von Buch, 'Jura Deutsch.,' " Berl. Akadem," 1837. "Posidonien- 

 Schiefer," Quenst., ' Flotzgebirge,' p. 538, 1843. "9'= Stage, Toarcien (pars infer.)," 

 d'Orbigny, ' Cours. Element, de Paleontol.,' p. 463, 1852. "Die Schichten der 

 Posidonomya Bronni," pars, Oppel, ' Juraformation,' p. 197, 1856. " Communis- 

 bed," Wright, ' Quart. Journ. Geol. Soc.,' vol xiv, p. 25, 1858. "Communis Zone," 

 Rev. Dr. Smithe, ' Cots. Club Trans.,' Aug., 1861. ' Serpentinus-bed,' Judd, ' Geology 



1 The zone oi Stephanoceras commune, named in p. 3, may be advantageously divided into the zones of 

 Harpoceras serpentinum, and Harpoceras bi/rons. 



