52 THE LIAS AMMONITES. 



In France this zone is so closely connected with other Lower Lias beds resting upon it, 

 that it has not been accurately defined and separated from them. Its specific Ammonite 

 forms have, however, been collected in difi'erent Departments. Thus, Arietites obtusus, 

 Arietites stellaris, Aegoceras Birchii, Aeg. planicosta, have been collected near Avallon, 

 Yonne ; and at Semur, Cote d'Or ; also at Couzon, near Lyons ; and at Nancy, Meurthe. 

 The same species were likewise collected, according to M. Dumortier,' from St. Fortunat, 

 St. Cyr, Rhone ; St. Christophe, Saone-et-Loire ; St. Rambart, Ain ; affording evidence 

 of the existence of this zone of life through a considerable area of the Sinemurian Lias. 



M. Marcou, in the Jura of Salins,^ described under the name " Marnes de Balingen 

 ou a Gryphsea cymbium " three stages resting upon the Tuberculatus-beds ; these 

 were — 1st, beds with Arietites obtusus ; 2nd, beds with Amaltheus oxynotus ; and 

 3rd, beds ^^'x^h Arietites raricostatus ; and these resembled the formation near Balingen, 

 so that in the Jura the Obtusus-zone is developed, as it is likewise in other localities in 

 Switzerland. 



6. The Zone of Amaltheus oxynotus. 



Synonyms. — " Oxynoten-Schichte," Fraas, ' Wiirttemb. naturw. Jahreshefte,' p. 206, 

 1847. "Die Schichten des Ammonites oxynotus,* Oppel, 'Die Juraformation,' p. 54, 

 1856. " Oxynotenlager," Quenstedt, 'Der Jura,' p. 293,1858. " Oxynotus-bed," 

 Wright, 'Quart, Journ. Geol. Soc.,' vol. xiv, p. 25, 1858. "Zone of Ammonites 

 oxynotus," Wright, 'Quart. Journ. Geol. Soc.,' vol. xvi, p. 406, 1860. "La Zone de 

 "V Ammonites oxynotus,'' 'DnmorWev, 'Etudes Paleont.,' t. ii, p. 238,1867. "Zone 

 oi Ammonites oxynotus," Tate and Blake, ' Yorkshire Lias,' p. 7, 1876. 



Gloucestershire. — This zone consists of beds of dark clays, which often contain much 

 ferrous sulphide and ferric oxide, and the fossils found in these clays are either highly 

 pyritic or charged with the peroxide of iron. This zone was exposed in cutting 

 the Bristol-and-Birmingham, and Great-Western Railways ; at Lansdown, near Chelten- 

 ham ; and in excavating the new docks at Gloucester ; I have collected its characteristic 

 fossils at Swindon and at some localities in the Valley of the Severn. 



Dorsetshire. — Amaltheus Lymensis, the representative species, in the ^o\xi\\,oi Amaltheus 

 oxynotus in the Midland Counties — is found in a thin bed of dark, pyritic marl between 

 Charmouth and Lyme Regis, near Black Venn. It is here collected with other species, 

 which properly belong to a higher bed ; the talus of the upper marl, from the decay of the 

 bank, making it difficult to separate the beds. 



Yorkshire. — The Oxynotus-zone, is well seen in Robin Hood's Bay, and the following 

 detailed section by MM. Tate and Blake,' including likewise the Obtusus-zone and 



^ ' iEtudes Paleont. Depots Jurassiques du Bassin du Rh6ne,' tome ii, p. 103, 1867. 



2 'Jura Salinois,' Mem. Soc. Geol. de France, 1846. 



3 'Yorkshire Lias,' p. 73, 1876. 



