306 LOWER EOCENE FORMATIONS OF FRANCE. [Ch. XYI. 



used for pottery, and called "argile plastique." Fossil oysters (Ostrea 

 bellovacind) abound in some places, and in others there is a mixture of 

 fluviatile shells, such as Cyrena cuneiformis (fig. 262, p. 296), Melania 

 inquinata (fig. 263), and others, frequently met with in beds occupying 

 the same position in the valley of the Thames. Layers of lignite also 

 accompany the inferior clays and sands. 



Immediately upon the chalk at the bottom of all the tertiary strata 

 in France there generally is a conglomerate or breccia of rolled and 

 angular chalk-flints, cemented by cilicious sand. These beds appear 

 to be of littoral origin, and imply the previous emergence of the chalk, 

 and its waste by denudation. In the year 1855, the tibia and femur of 

 a large bird equalling at least the ostrich in size were found at Meudon, 

 near Paris,, at the base of the Plastic clay. This bird, to which the 

 name of Gastomis Parisiensis has been assigned, appears, from the 

 Memoirs of MM. Hebert, Lartet, and Owen, to belong to an extinct 

 genus. Professor Owen refers it to the class of wading land birds 

 rather than to an aquatic species.* 



That a formation so much explored for economical purposes as the 

 Argile Plastique around Paris, and the clays and sands of correspond- 

 ing age near London, should never have afforded any vestige of a 

 feathered biped previously to the year 1855, shows what diligent 

 search and what skill in osteological interpretation are acquired before 

 the existence of birds of remote ages can be proved by more decisive 

 evidence than their footprints. 



Sables de Bracheux (C. 3, p. 298). — The marine sands called the 

 Sables de Bracheux (a place near Beauvais), are considered by M. 

 Hebert to be older than the Lignites and Plastic clay, and to concide 

 in age with the Thanet Sands of England. At La Fere, in the De- 

 partment of the Aisne, in. a deposit of this age, a fossil skull has been 

 found of a quadruped called by Blainville Arctocyon primwvus, and 

 supposed by him to be related both to the bear and to the Kinkajou 

 (fCercoleptes). This creature appears to be the oldest known tertiary 

 mammifer. 



JVummulitic formation of .Europe, Asia, <£c. — When I visited Bel- 

 gium and French Flanders in 1851, with a view of comparing the ter- 

 tiary strata of those countries with, the English series, I found that 

 all the beds between the Lower Miocene or Limburg formations and 

 the Lower Eocene or London clay proper, might be conveniently divided 

 into three sections, distinguished, among other pakeontological char- 

 acters, by three different species of nummulities, jV. variolaria in upper 

 beds, N. laevigata in the middle, and JV. planulata in the lower. Af- 

 ter I had adopted this classification, I found, what I had overlooked or 

 forgotten, that the superposition of these three species in the order 

 here assigned to them had been previously recognized in the .North 

 of France, in 1842, by Viscount d'Archiac. The same author, in 



* Quart. Geol. Journ., vol. xii. p. 204, 1856. 



