ZONE OF HARPOCERAS BIFRONS. 133 



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

 hitutnineuse." 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:^ 



f 1. Alternations of calcareous and marly beds with Harpoceras hifrons, Brug., H.falciferum, 

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

 Nucula Hammeri, Defr., Thecocyathus mactra, Edw. 

 2. Argillaceous schist and beds of argillaceous limestone from O'Ol ra. to 002 ra. thick 

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

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



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



Lias 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 serpentimm, Rein., Phyll. heterophyllum, Sow., Stephanoceras annulatum, 

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

 Voltz., and the skull and jaws of Ichthyosaurus. 

 ^3. Beds of limestone with Gryphcea cymhium, separated by thin beds of calcariferous clay. 

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

 I fimhriatum, Sow., Pecten aquivalvis, Sow., Terebratula (piadrifida, Sow., T. ringens, 



SecondStage: g^^ Rhyn. tetraedra. Sow., Rhyn. variabilis, Schloth., Spiriferina Walcotti. 



li^IDDLlj "s 



Lias I '^' Argillaceous marls, without fossils, with Septaria. 



I' 5. Limestone very argillaceous, with Belemnites clavatus, Blain., Bel. mnbilicatus, Blain., 

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

 L Walcotti, Sow., Aegoceras Bavoei, Sow., Aeg. Henleyi, Sow., Aeg. hybrida, d'Orb. 



fe. Limestones with Gryphaa arcuata. Lam., divisible into two beds. 



I a. Upper bed with Gryphcea arcuata, Lam., Arietites Bttcklandi, Sow. = bisulcatus, 

 Third stage: I Bmg., Rhyn. variabilis, &chloth. 



T^fJ^ I *• I'O^e'' I'ed with Gryphcea arcuata, Lam., Gryph. Maccullochii, Sow., Arietites 

 I bisulcatus, Arietites Coneybeari, Sow., Spiriferina Walcotti, and Pentacrinus 



1 basaltiformis. Mill. 



Lias 



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

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

 serpentinmi resting upon schists containing GryplicRa cymhium, and consisting of their 

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

 Pliylloceras lieterophylhm, rarely Harpoceras bifrons. Second zone with Harpoceras 

 complanatim. 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 



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



2 ' Bulletin de la Soc. G^ol. de France,' 2e serie, torn, ii, p. 664, 1843. 

 * 'Description Geologique de I'Auxoie,' p. 288, 1873. 



