28 Bulletin 15 330 



tain concretions of sulphate of strontium. Cyrena convexa some- 

 times occurs. These layers of the green clays are used for the 

 manufacfture of tiles. In their southward extension towards 

 E^tampes, the green clays become unfossiliferous. 



Brie limestone. The green clays are followed by the Brie 

 limestone, a freshwater formation containing, though rarely, 

 Linmcea cornea, Planorbis cormc, Nystia Dtichasteli and fruits of 

 Chara. The limestone forms most of the plateau of the Brie 

 which lies to the east of Paris. Near Argenteuil, at Sannois 

 and Orgemont, this freshwater limestone is replaced by marine 

 marls with Cerithium plicatu7n and Cytherea incrassuta. 



Sands of Fontainebleaii. The sands of Fontainebleau, with 

 a rich marine fauna, overlie the Brie limestone. The sands are 

 best developed in the vicinity of Ktampes. They have recently 

 been described* in much detail by M. Cossmann and M. Lambert. 



Oyster-shell marls. A sudden change from the freshwater 

 horizon of the Brie to marine conditions is indicated by the 

 oyster-shell marls, a littoral deposit at the base of the Fontaine- 

 bleau sands. These marl bedsf extend from Paris to Lonjumeau. 

 From that town southward to E^trechy, the deposit becomes 

 arenaceous and forms a friable sandstone. At the outskirts of 

 Paris, near Villejuif, the oyster-shell marls contain quantities of 

 Ostrea cyathula; but the larger species, O. longirostris, becomes 

 more common to the southward. In addition to these charadler- 

 istic species of Ostrea, Cytherea incrassata, Natica crassatina and 

 Cerithium plicatum are common in the marls. 



* Cossmann et lyambert, Etude Palepntologique et Stratigraphique sur 

 le Terrain Oligocene Marin aux Environs d'Etampes; Memoires de la Soci^te 

 Geologique de Fraiice, 3eme serie, tome III, ire partie, 1884. 



Cossmann, Description de deux especes nouvelles du tongrien des envi- 

 rons d'Etampes, /owr. de Conchyliolqgie, vol. XXVII, 1879, p. 436, pi. 13. 



Lambert, Sables Oligocenes d'Etampes, Bull. Sac. Giol. de Fr., 2enie 

 serie, t. IX, pp. 496-499. See also Ibid., 3eme serie, t. X, p. 501. 



tHebert, Ed., Notice sur les fossiles tertiaires du Limbourg et sur ceux 

 de la couche a Ostrea cyathula du bassin de Paris, Bull, de la Soc. Geo I. de 

 Fr., 2eme serie, t. VI, p. 459, 1849. 



Dollfus, Coupe geologique de Chemin de Fer de Mery-sur-Oise, Bitll. 

 Soc. Gcol. de Fr., 3eme ser., t. VI, pp. 266, -299. 



