OF THE PARIS BASIN. 23 



crystals, in places, of carbonate of lime, rhombohedral or 

 scalenohedral, but the latter rarely. Fossils are not recorded 

 from this level. 



Beds above the Marls of Nanterre. — Above the Marls of 

 Nanterre, M. G. Dollfus, in his paper on the Mery Railway,* has 

 established the existence of a thick mass of beds, exceeding 

 thirty feet in thickness, including at least forty separate beds, 

 which are divisible into four fossiliferous and four unfossiliferous 

 horizons ; and he has shown that these immediately underlie the 

 lowest beds of the Sables Moyens. The fauna is also more allied 

 to that of the Sables Moyens, since Potamides pleurotomoides, P. 

 Botiellii and Cerithiu/n defiticiilatum occur among other fairly 

 characteristic forms. 



11. SABLES MOYENS 



(sables DE liEAUCHAMP.) 



Immediately upon the Caillasses of the Calcaire Grossier is 

 a mass of sands, sandstones and marls, varying fiom thirty-two feet 

 to forty-nine feet in thickness and of considerable extent in the 

 Paris basin. Towards the east they extend nearly to Epernay, 

 they touch Verneuil (Marne), sweep round under Brie, pass 

 close to Paris (where they are in a rudimentary state), border 

 the Seine, extend to the Vexin, and are represented in the north- 

 west of the basin by several outliers.f 



Although not possessing the same commercial value as the 

 Calcaire Grossier, and, partly for that reason, not having been so 

 minutely sub-divided, the palaeontological and geological interest 

 attaching to the Sables Moyens is very considerable. The fauna 

 is rich and varied, and affords many points of resemblance with 

 those of beds of similar age, though not of similar lithological 

 composition, on the English side of the Channel. 



The beds constituting this formation are divided into three 

 stages, or horizons, as follows : — 



Upper . . . Horizon of Mortefoiitaine. 

 Middle ... ,, Beauchamp. 



Lower ... ,, Auvers. 



Or, taking the types from the districts where each horizon is best 

 developed, M. G. Dollfus % classes the levels as — 



Morfontian . . . (Upper) . . Type at Mortefontaine. 

 Ermenonvillian . . (Middle) . . Type at Ermenonville. 

 Auversian . . . (Lower) . . Type at Auvers (Oise). 



In any case a triple division is admitted, and the three horizons 

 are thus described by M. Goubert.§ 



* Dollfus, Bull. Soc. Giol. /->., 36. s^r., vol. vi. (187S), p. 275. 

 t. G. Qo\\{\i%,'Mem. Soc. Geol. de Normandie, Havre (1880), p. 593. 

 I Dollfus, IsA'm. Soc. Geol. de Normandie, H.-ivre (1880), p. 592. 

 § Goubert, h, ull. Soc. Geo!. Fr., 2". ser , t. xvii. (1S60), p. 141. 



