part 4] 



JURASSIC CHEOKOLO&T : LIAS. 



279 



folding, thus causing numerous local non-sequences. In the neigh- 

 bourhood of Radstock the sauzeanum zone, in which occurs the 

 large numbei" of ^jpiriferina lualcotU for which that place is noted, 

 may be found resting indifferently on any earlier zone down to 

 langportensis (White Lias, see Table X below). 



In the Kejmsham area, which lies in the middle of the district 

 under consideration, the Lias occupies a shallow syncline, and the 

 beds have not been denuded to the same extent as those on the 

 south and north. Chiefly in this area the faunal sequence of 

 the Sinemurian deposits has been determined. 



The Hettangian deposits, as a whole, are best displayed in an 

 area of which Bristol is the centre. 



In the following table it Avill be observed that the White Lias 

 is included with the Hettangian. In common with the late 

 Dr. A. Vaughan and the late Edward Wilson, I have always held 

 the view that, for palseontological reasons, the line dividing Lias 

 from Rhsetic (Hettangian from Rhsetian) should be drawn at the 

 base of the White Lias. Mr. Buckman, it may be remarked, has 

 exj^ressed the Yiew that the Hettangian should be regarded as the 

 final phase of the Trias — on the grounds of the biological characters 

 of Ammonites, the decadent characters of Psiloceras and allies, 

 and the new departure (anagenetic characters) of the Arietidse of 

 the Sinemurian. 1 



Table X. — Zones of the Lower Lias (Lower Part). 



Ages 



Zonal terms. 



Name of Index fossil. 



. f 



turneri. 



Arietites turneri (J. de C. Sowerby). 



< 



sauzeanum. 



Agassiceras sauzeanum (D'Orbigny). 



S 



scipionianum. 



Mtomoceras scipionianum (D'Orbigny). 





gmuendense. 



Coroniceras gmuendense (Oppel). 



hucklandi. 



Coroniceras hucMandi (J. Sowerby). 



^ 



rotiforme. 



Coroniceras rotiforme (J. Sowerby). 



m I 



conyheari. 



Vermiceras conyheari (J. Sowerby). 





angulata. 



Schlotheimia angulata (Schlotheim). 





liasicus. 



Alsatites liasicus (D'Orbigny). 



t, 



[megastoma. 



Wxhneroceras megastoma (Waehner)].^ 



M 



5 . 



johnstoni. 



Caloceras johnstoni (J. de C. Sowerby). 



planorhis. 



Psiloceras planorhis (J. de C. Sowerby). 



t 



Ostrea. 



Ostrea liassica Strickland, and its 







mutations. 



w 



tatei. 



Pleuromya faiet Richardson & Tutcher.^ 





langportensis (White Lias). 



Volsella langportensis, Richardson & 



I 





Tutcher.3 



^ Not found in the district, but a Waehneroceras fauna occupies this posi- 

 tion elsewhere. See p. 280. 



2 Proc. Yorkshire Geol. Soc. vol. xix (1916) p. 52 & pi. viii, &g. 3. 

 '^ Ibid. p. 54 & pi. ix, fig. 11. 



Jurassic Time ' Q. J. G. S. vol. liv (1898) pp. 444-4 '3 



