ZONE OF HARPOCERAS BIFRONS. 



133 



First Stage 



Upper -<| 



LlA,S 



In the Yonne M. Cotteau^ calls this series " Lias superieur masse argilo- 

 bitumineuse" The following section, made at Vassy, from the summit of the hill to 

 the plain which surrounds the town of Avallon, exhibits the sequence and relation of 

 the Upper, Middle, and Lower Lias as developed in Yonne and described by M. Moreau, 

 " Reunion extraordinaire a Avallon (Yonne) Soc. Geol. de France," 1845 •? 



Alternations of calcareous and marly beds with Harpoceras bifrons, Brug., H.falciferum, 

 Sow., Lytoceras cornucopice, Sow., Turbo ornatus, Sow., Posidonomya Bronni, Voltz,, 

 Nucula Hamtneri, Defr., Thecocyathus mactra, Edw. 



Argillaceous schist and beds of argillaceous limestone from 0*01 m. to 002m. thick 

 alternate throughout this bed; the lower bed, of 0'40m. to 080 m., is worked 

 especially for the manufacture of the Ciment de Vassy. Veins of the carbonate of 

 lime traverse all the mass of the hill, parallel with each other, and directed 

 E. 40° N., like the soulevement of the Cote-d'Or, inclining to the W., where they 

 rise towards the ancient mass of Morvan. The fossils in these beds are common to 

 No. 1 and 2. 



Harpoceras serpentinum, Rein., Phyll. heterophyllum. Sow., Stephanoceras annulatum, 

 Stephan. commune, Stephan. Desplacei, d'Orb., Aptychus, Posidonomya Bronni, 

 Voltz., and the skull and jaws oi Ichthyosaurus. 



Beds of limestone with Gryphcea cymbium, separated by thin beds of calcariferous clay. 

 Belemnites are very abundant, with Amaltheus margaritatus, Mont., Lytoceras 

 Jimbriatum, Sow., Pecten eequivalvis, Sow., Terebratula quadrifida. Sow., T. ringens, 

 Sow., Rhyn. tetraedra. Sow., Rhijn. variabilis, Schloth., Spiriferina Walcotti. 



Argillaceous marls, without fossils, with Septaria. 



Limestone very argillaceous, with Belemnites clavatus, Blain., Bel. umbilicatus, Blain., 

 Bel. Bruguierianus, d'Orb., Terebratula nuDiismalis, Lam., Rhyn. rimosa, Spiriferina 

 Walcotti, Sow., Aegoceras Davoei, Sow., Aeg. Henleyi, Sow., Aeg. hyhrida, d'Orb. 



Limestones with Gryphcea arcuata. Lam., divisible into two beds. 



a. Upper bed with Gryphcea arcuata. Lam., Arietites Bucklandi, Sow. = bisidcatus, 

 Brug., Rhyn. variabilis, Schloth. 



b. Lower bed with Gryphaia arcuata, Lam., Gryph. Maccullochii, Sow., Arietites 

 bisidcatus, Arietites Coneybeari, Sow., Spiriferina Walcotti, and Pentacrinus 

 basaltiformis, Mill. 



r3. 



SecondStage: 

 Middle ■{ 

 Lias | 4. 

 5. 



L 



Third stage 

 Lower -{ 

 Lias 



L 



In the Cote d'Or a similar condition of the Posidonomi/a-heds prevails at Flavigny, 

 where M. Collenot says' an exposure by erosion shows — First, the zone with Harp, 

 serpentinum resting upon schists containing Gryphcea cymbium, and consisting of their 

 paper-like shales without bitumen. Here are found, also, Stephanoceras Holandrei, 

 Phylloceras heierophyUiim, rarely Harpoceras bifrons. Second zone with Harpoceras 

 complanatum. The rock is less bituminous and more aluminous than the preceding, and 

 the fossils are large and widely distributed throughout the beds. The third zone is 

 characterised by Pecten pumilus and Turbo subduplicatus, which is limited to this one 



^ ' Etudes sur les Echinides Foss. de Depart, de I'Yonne,' p. 32, 1849. 

 2 ' Bulletin de la Soc. Geol. de France,' 2e serie, tom. ii, p. 664, 1843. 

 2 ' Description Geologique de I'Auxois,' p. 288, 1873. 



