UPPER LIAS. 



85 



1 2. The Zone of Ammonites spinatds. 



St/iionyms. — Upper portion of the "Marlstone" of Englishauthors. "Marnes aPlicatoles," 

 Marcou, 'Jura Salinois/ p. 51. " Amaltlieenthone (pars, sup.)," Quenst. " Die Schicliten 

 des Ammoniies spinatus," Oppel, ' Juraformation,' p. 138. " Spinatus-bed," Wright, 

 ' Quart. Journ. Geol. Soc./ vol. xiv, p. 25. 



This zone is so closely united with the Marlstone that it appears to form its upper 

 portion, lithologically it is a light-coloured friable bed, containing many large fossiliferous 

 nodules. Ammonites sjnnaUis, Brug., Beleimiites hrevifonnis, Ziet., Lima Ilermanni, Voltz., 

 Terehratula punctata. Sow., and Spirifcr rodratm, Schloth., are the prevailing forms. — 



In Down Cliff the spinatus bed lies immediately in contact wdth the indurated marl of 

 the Upper Lias containing Ammonites serpentinus, Reinecke, and other Upper Lias forms 

 (see p. 77). 



THE UPPER LIAS. 



I include all the marly, argillaceous, and arenaceous deposits found between the Marl- 

 stone and Inferior Oolite in the Upper Lias, and group these beds into two stages, each 

 of which contains a special fauna. 



The lower zone is, in general, an argillaceous formation, with occasional and inconstant 

 bands of calcareous nodules ; the fossils of this division are nearly all specifically distinct 

 from those of the Marlstone on which it rests. The Ammonites of the group Capricorni 

 are all absent from these beds ; and in their stead have appeared great numbers of the groups 

 Falciferi and Planulati. In England one of the most prevailing species of the latter is 

 the Ammonites commimis, Sow,, from which I have derived the name of the stage. 



The upper zone in England is essentially an arenaceous formation, and although it 

 possesses some species in common with the zones of Ammonites communis below, and 

 Ammonites Murehisonce of the Inferior Oolite above, it nevertheless contains a fauna 

 sufficiently numerous in special forms to justify its separation from the Am. communis 

 stage. Most of the Ammonites of the upper zone belong to the group Falciferi ; a few, 

 however, are common to both, those of the group Lineati found herein are special to this 

 zone, one of the most characteristic of which is the Ammonites Jurensls, Ziet. 



