ZONE OF HARPOCERAS BIFRONS. 



127 



Gasteropoda. 



Eucyclus capitaneus, Munst. 

 Trocluis bisertns, Phil. 

 Cerithium, sp. 



Pleurotomaria subdecorata, Milnsf. 

 Rostellaria, sp, 

 Natica, sp. 



14. Zone of Harpoceras bifrons. 



Synonyms. — "A. communis-hedi,'^ part, Wright, ' Quart. Journ. Geol. Soc./ vol. xiv, 

 p. 25, 1858. " Zone of Am. communis^'' part, Wright, 'Oolitic Asteroidea,' Palaeont. 

 Soc, p. 38, 1862. " Zone a Am. bifrons," Reynes, ' Geol. et Paleont. Aveyron,' p. 65, 

 1868. " Leda-ovum-heAi," Judd, " Geol. of Rutland," ' Mem. Geol. Surv.,' p. 80, 1876. 

 "Zone of Am. communis or Alum-shale," Tate and Blake, 'Yorkshire Lias,' p. 181, 

 1876. 



This zone at Erocester Hill consists of fine sandy marls, with inconstant bands of a 

 harder sand rock, which form several layers of nodules in the bank, and many of these 

 contain fossils. I have found sometimes clusters of Harpoceras bifrons in some of these 

 masses when broken up — a fact which first taught me the true stratigraphical position of 

 Harp, bifrons. Along other escarpments of the Cotteswolds I have collected Harp, 

 bifrons in brownish marl at the southern base of Crickley Hill, and in soft grey clays 

 above the Serpcntinum-heA at Stinchcombe Hill. 



In the Saltwick profile near Whitby, and at Rock Cliff, near Staithes, on the York- 

 shire coast, we have already seen that Harp, bifrons belongs to the alum shale, and has 

 for its associates Stephan. commune, Belemnites Voltzii, Leda ovum, and Gresslya donaci- 

 formis, and that it there forms a well-marked horizon of life resting upon the Jet-rock, 

 with Harpoceras serpenlinum, and Harp, falciferum. 



On cutting the eastern portion of the Banbury and Cheltenham Direct Railway some 

 instructive sections of the Upper Lias have been exposed on nearing Bloxam, Oxfordshire. 

 Mr. Beesley^ notes, " about 300 yards before reaching the Barford-road Bridge, a small fault 

 brings down the Upper Lias about four feet against the Spitiatus-heds. For 100 yards 

 further the banks are all Marlstone of this zone ; then comes another fault, dipping to the 

 east, which throws down the Upper Lias to the base of the section, a depth of fifteen feet ; 

 the white marly limestone of the Serpen linum-heds, crowded with Harpoceras bifrons, 

 Stepltanoceras commune, Lytoceras cornucopia, Phylloceras heterophyllum, PJiyll. subcarina- 

 tum, and species of the Serpentinum group, with Belemnites llminsierensis and B. reyularis 

 and Nautili, now forming the floor of the line, and over it blue or green shale fifteen feet 

 thick. The faults pass obliquely across the line from north-west to south-east." 



1 "Geology of the Banbury and Cheltenliam Railway," ' Proc. Geol. Assoc.,' vol. v, 1877. 



