ZONE OF LYTOCERAS JURENSE. 



137 



The following typical section of the Upper Lias, " V etage Toarcien,'' was made by 

 Professor Alcide d'Orbigny at Thouars, Deux-Sevres/ where the daily working of the 

 beds exposes beautiful natural profiles. The relation of the Jurense and Serpentinum 

 zones are here likewise well seen in situ. 



Section or the " Toarcian " at Thouars, Deux-S^ivres. 



No. 



1 



2 

 3 



4 

 5 

 6 



7 

 8 



9 

 10 



Petrology. 



Thick- 

 ness. 



Organic Remains. 



Thick bed of very white argillaceous 

 limestone, containing flint 



Limestone and argillaceous clay 



Alternate beds of bluish clay and lime- 

 stones, passing at the upper part into 

 a ferruginous clay 



Blue clay 



Grey granular limestone 



Compact limestone 



1 

 1 



1 



? 

 ? 

 ? 



7 

 ? 



? 



Belemnites tripartitus. 



Lytoceras jurense. 



Harpoceras insiffne, Harpoceras radians, Belem- 

 nites irregularis. 



Harpoceras variahile, Belemnites tripartitus. 

 Harpoceras Thouarsene. 

 Non-fossiliferous. 

 Harpoceras serpentinum. 



Thin beds of ferruarinous clav 



Thick bed of sandy limestone, raised 

 for building-material 



Bed of foliated saccharoid limestone ... 



Thick bed of yellow limestone, with 

 some grains of quartz, the lowest bed 

 of I'etage Toarcien 







15. The Zone of Lytoceras Jurense. 



Synonyms. — " Sands of the Inferior Oolite," Smith, De la Eeche, Conybeare, and other 

 English authors. " Jurensismergel.," Quenst., ' Flozgeb. Wiirtemberg,' p. 599, 1843. 

 " 9* etage Toarcien (pars sup,)," d'Orbigny, 'Cours element, de Paleontologie,' p. 469, 

 1852 (sect, at Thouars U to/). " Zone des Amm. iorulosus und Zone des Avun. Jurensis," 

 Oppel, ' Juraformation,' p. 296, 1856. "Cephalopoda-bed and Upper-Lias Sands," 

 Wright, 'Quart. Jour. Geol. Soc.,' vol. xii, p. 292, 1856. " Marnes d'Aresche, et 

 Marnes de Pinperdu, Jura franc-comtois," Marcou, ' Les Roches du Jura,' p. 119, 1857. 

 " Ammonite Sands," Hull, ' Mem. of the Geol. Surv., Country around Cheltenham,' p. 

 25, 1857. " Cynocephala stage," Lycett, ' Cotteswold Hills/ p. 16, 1857, " Jurensis 

 bed," Wright, ' Quart. Jour. Geol. Soc.,' vol. xiv, p. 25, 1857. " Lias Zeta," Quenstedt, 

 ' Der Jura Uebersichtafel,' p. 293, 1858. " Zone of ^w. /«r<^;w2>," Wright, ' Oolitic 

 Asteroida, Pal. Soc' Vol. 1862. "Midford Sands," Phillips, ' Geol. of Oxford and the 

 Valley of the Thames,' p. 118, 1871. 



This younger member of the great Lias formation is well developed in the counties 



^ ' Cours .Element. Paleoutologie,' torn, ii, p. 4G9. 



18 



