6 THE EOCENE BEDS 



developed in Picardy between the Oise and the Somme, which 

 has formed the subject of a special work by M. De Mercey.* 



At Chalons-sur-Vesle,t Jonchery, Brimont, &c., a bed about 

 thirty-two feet in thickness of yellowish grey sandstone in three 

 divisions is found reposing on the chalk; whilst above come thirty- 

 two to thirty-nine feet of siliceo-calcareous sands with a rich fauna 

 at the first mentioned place, including Corbiila regidbiensis, Proto- 

 cardia Edtvardsi, Ostrea bellovacensis and Beloptera Levesquei. 

 At Jonchery also the sands are exceedingly fossiliferous. 



5. RILLY LIMESTONE. 



At Rilly-la-Montagne, near Rheims, a series of beds is found on 

 the Chalk, and their precise position in the Tertiary series has 

 long been a matter of dispute with geologists. The following is 

 a section of the large sand-pit at that place. 



Section at Rilly.X 



k. Yellow sand. 



j. Bluish clay. 



i. Lignites with Cyrena. 



h. Yellow, blue or brown clay, reposing on white mail ; the surface of 



this clay is clearly marked. 

 g. White marl, very argillaceous, sometimes yellowish, without 



calcareous concretions, worked for hydraulic lime. 

 /. Bluish clay, plastic, irregular, but with a horizontal surface. 

 e. Marl, with numerous small concretions of crystalline limestone, 



without fossils, makes a poor hydraulic lime, and at the base 



has blocks of hard yellowish crystalline limestone full of 



fossils. 

 d. Yellow sand. 

 c. Very pure white sand, without pebbles or fossils, but with angular 



fragments of hyaline quartz. 

 b. Ferruginous sand, sometimes agglutinated, with pebbles and 



impressions of Cardium. 

 a. Chalk, having its surface pierced by boring mollusca. 



The lower beds of this section, as at other exposures in the 

 vicinity, have yielded marine fossils very analogous to those 

 of Brimont, Jonchery, Chalons-sur-Vesle and Bracheux. The 

 bed e is the type of the celebrated Marl and Limestone of Rilly, 

 with the remains of land and marsh-loving mollusca such as 

 Viviparus aspersus. Physa gigantea and Helix hemisphcerica. The 

 bed / with Cyrena indicates the presence of the " Lignites," and 

 seems to us to fix clearly the horizon of the Rilly Limestone. The 

 same class of evidence is obtainable at other spots in the neigh- 

 bourhood, and, bearing in mind the relationships to and intervention 

 of the marine sands beneath them, it is difficult to see on what 

 grounds the Rilly Marl and Limestone can be placed at the base 



* De Mercey, Bull. Soc. Geol. Fr., 36. s^r., t. viii. (1880), p. 26. 



t For details of this section, see Gosselet, Bull. Sc-^t/. Carle Geol. France, Paris (No. S, 

 January, 1890), p. 7. 



X G. Dollfus, Ann. Soc. Geol. du Noyd, t. iii. (1875), p. 159 ; also Hebert, id. (1S74). 



