OF THE PARIS BASIN. 39 



Falun (Yellow earthy sand with Trochus ; falun with ft. in. 



of < AJeretrix mcrassata, Potamides pl!catiis,ik,c. 5 - 



Jeurre. I Yellowish marly sand with Amp. crassa/ina . o 8 



Molasse of | e J ^ -.l /l ^ ,/ r ^i . ^ 



p. 1 , 1 'Sandstone with Uslreacyathula (base not seen} i o 



M. Tournouer has given* an interesting account of the 

 general nature of the fossils found ; whilst the following species 

 may be cited as truly characteristic of the horizon of the falun 

 of Jeurre — Gastrochcena Raulini, Syndesmya Satidbergeri, Mere- 

 trix stampinensis, Lima Klipsteini, Conns symmetriciis and Dcs- 

 hayesia paristensis. 



The lower members of the P^tampes Oligocenes are also met 

 with at Versailles and Neuilly-en-Vexin, where the fauna has been 

 compared with that of the falun of Jeurre : whilst M. Tournouer 

 places the beds of St. Christophe-en-Halatte on this horizon. 



5. SANDS OF MORIGNY. 



The typical section of this horizon occurs in a copse, the posi- 

 tion of which is explained on p. 56. All that was visible at the 

 time of our visit consisted of a few feet of grey or white sand, full 

 of fossils of but few species. The most abundant of these were, 

 Potaniides trochkaris, P. plicatm;, var. Galeotti (occurring in 

 thousands, all very small), and Bayania se/nidecitssafa. The 

 specimens of Potamides trochkaris are very remarkable, the outer 

 shell being worn away, and only the columella left with the spiral 

 divisions winding round it, so that the species resembles a screw 

 having a very exaggerated, close thread ; this is entirely characteris- 

 tic. Other fossils are Axincea obovata, Typhis cuniculosus, Lampusia 

 flandrica., and, rarely, VolutilitJtes Rathieri and Axincea angusti- 

 costata. The Morigny sands are developed (as will have been 

 noticed) in the sand-pit at Jeurre {supra) ; and are also found at 

 St. Phalier, and Faubourg St. Michel, Etampes. 



Sands of Fontenav. 



The faluns of Jeurre, and sands of Morigny of the Etampes 

 district are represented in the environs of Paris by a deposit known 

 as the " Sands of Fontenay," from the village of Fontenay-aux- 

 Roses, where they are typically developed. They are essentially 

 yellow sands, practically unfossiliferous, of considerable thickness, 

 and have a wide horizontal extension round the French metro- 

 polis, forming the foundations of almost all the new forts. Other 

 sections worthy of note are at Chatillon and Romainville. 



Sands and Sandstones of Fontainebleau. 



Succeeding the sands of Fontenay, we have the sands and sand- 

 stones of Fontainebleau. M. Ch. d'Orbigny showed the difference 



* Tournouer, Bull. Soc. Gcol. Fr., 36. s^r., t. vi. (1878), p. 672. 



