112 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Ft. in. 

 Corbula gallica, Lucina saxorum, Cerithium tuber- 

 culosum, C. mutahile, C. tricarinatum, Cyclostoma 



mumia, himncea longiscata, &c. : average 50 



5. Greenish-gre}^ sandy marls, full of marine shells 1 6 



6. Green marl 3 



7. Conglomerate bed — Fistularia 6 



78 



M. Graves gives no exact measurement of the Sables moyens in 

 the Oise, but he states that they may there be distinctly divided, 

 commencing at the top, into — 



1 . Alternating beds of sand and sandstone, sometimes calcareous, 



marly, and pebbly*; numerous organic remains, and oc- 

 casional subordinate thin beds of green marl and lime- 

 stones with freshwater shells f- 



2. A central thick mass of quartzose sands and sandstones, with- 



out organic remains, exceptmg pieces of wood. 

 ^. An argillaceous brownish sandy marl and sands, rich in organic 

 remains, containing, as subordinate and occasional beds at 

 the base of the series, — 1 . Green and brown marls. 2. Con- 

 glomerate of worn flints, flint-pebbles, pebbles of the Cal- 

 caire grossier, and of the sandstone of the " Sables Infe- 

 rieurs." 



In the upper beds the principal characteristic fossils are — Trochus 

 monilifer, Solarium trochiforme, Cerithium Cordieri, C. thiarella^ 

 C. Roysii, C. pleurotomoides, Modiola seminuda, Chama papyracea, 

 Avicula fragilis, Paludina nana, Cyrena deperdita, Oliva Laumon- 

 tiana, Ostrea cubitus, and the Fortunus Hericarti and Lichenopora 

 crispa; and in the lower beds — Cerithium trochiforme, C. tubercu- 

 losum. Conns scabriusculus, Valuta Branderi, V. digitalina, Ampul- 

 laria ponderosa, Chama turgidida, Venericardia cor-avium, Corbula 

 umbonella, Sanyuinolaria Lamarckii, Ostrea arenaria, and Nwnmu- 

 lites variolarius. 



A peculiar feature of the fossils of the upper division is their usually 

 small size. In some of the subordinate masses of hard grey concre- 

 tionary sandstone I have found freshwater shells (LimncBa) and flint- 

 pebbles, in some number J. It is remarkable in places for the 

 abundance of a species of Crab — the Portunus Hericarti, Desm. 



In the central beds there are found pieces of silicified wood often 

 many feet in length. The blocks of sandstone also sometimes show 

 rootlet-like traversings, as well as vegetable impressions on the broken 

 surfaces. These sandstones, generally void even of such organic re- 

 mains, are largely worked for paving-stones. 



The fossils of the lower division are often stained yellow, and the 

 shells are somewhat thicker than those of the Calcaire grossier. In 

 the conglomerate at the base of this division remains of the older 



* Op. cit. p. 452. t Ibid. p. 456. 



X At Nauteuil-le-Haudouin the top sandstones alternate with beds of fresh- 

 water limestone. — Op. cit. p. 435. 



