ZONE OF AEGOCERAS HENLEYI. 87 



10. The Zone of Aegoceras Henleyi. 



Synonyms. — "Upper Marls " (pars med.), De la Beche, ' Geol. Trans.,' 2nd ser., vol ii, 

 p. 23, pi. iii, 1823. "Der mittlere schwarze Jura," Quenstedt, pars, ' Flotzgebirge 

 Wiirtt.,' p. 172, 1843. " Die Schichten des Amm. Davoei'' Oppel, ' Juraformation,' 

 p. 126, 1856. "Schiste d'Ethe," Dewalque, 'Lias de Luxembourg,' p. 55, 1857. 

 " Lias Gamma" (pars Davoeikalk), Quenstedt, "Der Jura Uebersichstafel,'' p. 293, 1858. 

 " i)«!yffi2-bed," Wright, 'Quart. Journ. Geol. Soc.,' vol. xiv, p. 25, 1858. "Zone of 

 Am. Caprkornus'^ Wright, ' Oolitic Asteroidea.' Pal. Soc., vol. for 1861, p. 79, 1863. 

 " Zone de la Belemnites davatus" pars Dumortier, ' Etudes Paleontologiques sur les 

 Depots Jurassiques du Bassin du Rhone,' 3me partie, Lias Moyen, p. 16, 1869. "Die 

 Schichten des Ammonites Davcei" Brauns, 'Der untere Jura,' p. 124, 1871. "Zone 

 of Ammonites Capricornus " Tate and Blake, ' Yorkshire Lias,' p. 89, 1876. 



This zone is very vi^ell developed in England ; and wherever the Middle Lias is 

 complete it is found beneath the rock-bed forming the " Marlstone " of British Geologists. 

 The beds consist of laminated clays, sometimes containing micaceous particles, or they are 

 largely charged with ferric oxide, whilst in other localities the zone is represented by 

 irregular beds of brown micaceous sandstone. The inconstant stony bands found in the 

 clay contain sometimes an assemblage of fossils, and in a few of the beds several interesting 

 forms of Asteriadce and Oplmiridce have been found. At Mickelton,^ Worcestershire, 

 where the shales of this zone were perforated for a railway tunnel, a considerable number of 

 fossils in fine preservation were obtained; the shales, partly arenaceous and partly micaceous, 

 formed thin slabs of fine bluish sandstone, on which many of the Pentacrinites, Brittle-stars, 

 and Starfishes, lay in high relief. There were also large slabs of ironstone, many inches 

 in thickness, composed almost entirely of shells, with many immature specimens of 

 Aeyoceras Henleyi. All the specimens of Ur aster Gaveyi, Forb., Tropidaster pectinatus, 

 Forb., Ophioderma Gaveyi, with Cidaris Edwardsii, Wrt., and Pentacriniis robmfus, 

 Wrt., were found adherent to the under side of a thick slab of ironstone which lay twenty 

 feet below the surface. The Cidaris, and its spines attached to the tubercles of the 

 plates and the ossicles, and species of Urasier, Tropidasier, and Ophioderma were as well 

 preserved for anatomical description as if tiiey had been prepared by a taxidermatist for 

 the purpose. 



Beds of laminated shales and ferruginous clays, the equivalent in age of those at 

 Mickelton, were exposed in making excavations at Hewlett's Hill for the reservoirs of 

 the Cheltenham water- works ; many of the ironstone bands were full of fossils in various 

 stages of decay, from the decomposition of the calcareous matter of the shell. Another 

 exposure on the same contour line was made at Witcombe, and several of the Ammonites 



> "On the Railway Cuttings at Mickelton Tunnel, &c,," by G. E. Gavey, F.G.S., 'Quart. Journ. 

 Geol. Soc.,' vol. i.x, p. 29, 1853. 



