2 THE EOCENE BEDS 



It will be seen from the above that the Banc Vert proper 

 (No. 4) is underlaid and overlaid by limestones, the lower called 

 Saint-Nom in some districts, or base rock {roche-dii-bas) in 

 others, as in the Aisne quarries ; while in other quarries, as 

 Vaugirard, Bagneux, and elsewhere, it is called " liaisT The 

 upper limestone is called clicquart in many quarries, or top-rock in 

 the Aisne district {roche-du-hani), and occasionally '■'■ liais" as in 

 the St. Denis quarries.* 



Both these limestones yield some of the most excellent 

 building materials of the basin, and they are almost exactly 

 similar both lithologically and in the fossils which they contain. 



One of the most interesting facts in connexion with the Banc 

 Vert is the introduction of fresh-water beds with characteristic 

 fossils. As we have already indicated, the neighbourhood of 

 Provins has a lake-like expanse of beds, which are well developed 

 in Seine-et-Marne, and are referred to this horizon. Dissostoma 

 mumviia is a frequent fossil, both in the neighbourhood of Paris and 

 Provins, at this level ; while in the more fresh-water strata of the 

 latter district, Planorbis pseudoajmnonhis, P. Chertiert, Viviparus 

 novigentiensis, V. Orbignyi, Liinncea Michelini and Helix Edwardsi 

 are abundant. 



The fauna of the Banc Vert is rich in Vertebrata and Mollusca, 

 while in certain areas, as at Vaugirard, Senlis, and elsewhere, a 

 bed of lignite is found, filled with vegetable impressions and 

 with carbonised wood passing into a true lignite. 



In Dr. Hovelacque's notes there are recorded from Issy, 

 Marine Algae, e.g. Zostera, and Terrestrial flora, such as Nipadites, 

 Potamogeton (?), Dryandra, Flabellaria and Pinus parisiensis. 

 The Vertebrata include such interesting forms as Lophiodon paris- 

 iensis and Dichobuntis suil/us, which, together with Pachynolophus, 

 have been recorded from this horizon at Nanterre and Passy. 

 Fish remains are not uncommon, including Carcharodon disauris, 

 Pristis parisiensis and Labrax ?najor. 



The Mollusca, in addition to the fresh-water forms already 

 cited, include the characteristic Potamides lapiduni with its 

 varieties, Mesalia fasciata also of very variable character, and 

 some distinctive Cerithidae, as Ceriihium Gravesi, C. serratum, 

 Potamides angulosus, P. interruptus, P. cakitrapoides. 



^"^ Bancs francs" and '^ Roche" de Paris. — The Bancs francs, 

 with the overlying bed called Roche de Paris, are well developed 

 to the south of Paris, as at Gentilly and Arcueil,t and were 

 formerly worked for building material, but the best stone is now 

 exhausted and the quarries are unworked. The series is formed 

 by alternations of marly beds with calcareous sands, in part 

 indurated. 



The fauna is characteristic and principally Cerithidae ; such 

 species as C. de?iticulatn/n, P. angu/osHS and P. cristatus are com- 



* Stan. Meunier, Gi'ol de Paris (1875), p. 181. t See Section p. 21. 



