30 THE EOCENE BEDS 



vuniiniia, Planorbis goniobasis and Hyd7-obia pitsilla, occur. To 

 the north of Paris the stone is occasionally quarried for road-metal. 



In the environs of Rheims the formation is composed of marl?, 

 clays, and more or less siliceous limestones, passing frequently 

 into the mculiere with Linmcea longiscata and Z. acuminata. 

 M. de Lapparent says* that the same beds at Germaine, near 

 Epernay, contain lenticular pieces of hard clay. Towards the 

 south we find on this level ihe fibrous limestone of Provins which 

 passes into the marble of Givray. 



At Paris the St. Guen limestone is very variable in character. 

 M. Michelot has shevvnf from a section in the Avenue de I'lmper- 

 atrice that, although it was only twenty-four feet in thickness, it con- 

 tained no less than thirty-six distinct beds. A good exposure along 

 the Boulevard Malesherbes has been described by M. Goubert ;+ 

 here the beds were chiefly marls and difticult to correlate with 

 those on the same horizon even in the immediate vicinity. Other 

 noteworthy developments of the St. Ouen beds have been 

 chronicled by MM. G. Dollfus and Vasseur in their celebrated 

 work§ on the geological section along the Mery-sur-Oise railway, 

 between Valmondois and Bessancourt (Seine et Oise) ; by 

 MM. Carez and Vasseur|| at La Frette-sous-Cormeilles ; and 

 M. de BouryTI at Magny. 



13.— GYPSUM BEDS AND MARLS. 

 The alternating beds of gypsum and marls which have such an 

 enormous extension in the Parisian area, although normally found 

 above the St. Ouen limestone or the local sands of Monceaux, 

 sometimes repose directly on the Sables Moyens. The total 

 thickness of the formation varies from i8o feet at Sannois and 162 

 feet at the classical section of Montmartre, to 100 feet at Mont- 

 morency and 50 feet on the plateau of Carnelle. 



Where the succession is unbroken the sections usually pre- 

 sent the following : — 



Sub-divisions of the Gypsum beds and mat-Is. 



10. White marls of Pantin with Limncea strigosa, remains 



of birds, &c. ........ 



9. Blue marls with pyrites ...... 



8. First mass of evpsum with Palcrollierium . . . ■ t • ^ r 



,, ,, , ^■'•r, a- . ! Limestone of 



7. Yellow marls with timts . . . . . • ' (^1 • . 



6. Second mass o{ ^y^^'iVi\Vi. \^\\.\\ Ceritliium VA'xxXs . .\ ' I » J* 



5. Marls with Liicina ....... 



4. Tliird mass of gypsum ...... 



3. Yellow marls with Pholadomya liidensis 



2. Fourth mass of gypsum ...... 



I. Green sands of Monceaux and Argenteuil with 



Mytiliis Biocliei ....... 



* De Lapparent, Tr. de GeoL, 2 ed. (1S85), p. 1137. 



t Michelot, Bull. Soc. Geo/. Fr., 2c. sen, t. .\ii. (1855), p. 1314 



t Goubert, BzeU. Soc. Geol. Fr., 2e. s^r., t. xviii. (1S60), p. So.' 



§ Dollfus and Vasseur, id. 3e. s6r., t. vi. (1878), p. 243. 



II Carez and Vasseur, i i. 3e. sen, t. iv. (1876), p. 472. 



^ De Boury, id. 36. si5r., t. xii. (1834), p. 673. 



