34 



THE OLIGOCENE BEDS 



THE OLIGOCENE BEDS. 



Frenxh authors are not agreed as to the exact hmits of the Eocene 

 and Oh'gocene beds in the Paris basin, a divergence of opinion 

 which arises from the circumstance that the passage from the one 

 to the other series is very gradual The following may be given 

 as embodying the views of a few leading geologists on this 

 subject : — 



D nil's ions of the beds. 



Classi_ficat.'on of \ Classification of M. de 

 \MAL Cossmami and\ Laf parent* and the 

 I Lavihert * and Geol. Sumey of 



Dollfus.^ France. % 



Brie limestone . 

 Green marls 

 Supra-gvpseous marls 

 Lacustrine gypsum . 

 Marine gypsum 

 Sands of Monceaux . 

 Limestone of St. Ouen 

 Sands of Beauchamp 



Oligocene (^pars.') 



Eocene {pars.') 



Oligocene (^pai-s.) 



Eocene (^pars.') 



It is not our intention to discuss the various points at issue, 

 but we shall adopt the views of the officers of the French 

 Geological' Survey in regard to the matter both in our text and in 

 the accompanying map ; and we will now glance at the geograph- 

 ical distribution of the Oligocene as thus defined. I'he main mass 

 roughly occupies the southern half of the Paris basin ; conamenc- 

 ing at Montargis, the boundary runs northwards through Mont- 

 ereau, Villenauxe, Sezanne, Avize, Verzy ; thence westwards 

 through Ville-en-Tardenois, Meaux, Ecouen, Mantes; then turning 

 south passes by Houdan, Nogent-le-Roi, Chartres, and near 

 Bonneval. On the southern limits of the basin, the Oligocene 

 passes under the Miocene of the Loire, and thus leaves the region 

 now under consideration. Formerly, however, the Oligocene beds 

 must have had a much wider extension, for many outliers occur 

 outside the boundary just laid down, especially on the northern 

 part of the basin. A glance at the map will show this. 



* Cossmann and Lambert, Man. Soc. Gcol. Fr., 36. ser., t. iii. (1884), table facing p. 44. 



t Dollius, Biiii. Soc. Geol. Fr., 36. s6r., t. vi. (1878), pp. 269-293. 



X De Lapparent, lr.de. Geol., ed. 2, (1885) pp. 1138, iif6. 



§ Various publications, Carte Geol. de France, scale i^ q ^"^57; ,j ' &c. 



