276 
ELEMENTS OF GEOLOGY. 
other localities of the Sables inferieurs ” of Archiac, I agree 
with Mr. Prestwich, that the latter are probably newer than 
the London clay, and perhaps older than the Bracklesham 
beds of England. The London clay seems to be unrepre¬ 
sented in the Paris basin, unless partially so, by these sands."^ 
LOWER EOCENE FORMATIONS OF FRANCE. 
Argile Plastique (C. 2, p. 252).—At the base of the tertiary 
system in France are extensive deposits of sands, with occa¬ 
sional beds of clay used for pottery, and called “ argile plas¬ 
tique.” Fossil oysters {Ostrea bellovacina) abound in some 
places, and in others there is a mixture of fluviatile shells, 
such as Gyrena cuneiformis (Fig. 216, p. Melania in- 
quinata (Fig. 217), and others, frequently met with in beds 
occupying the same position in the London Basin. Layers 
of lignite also accompany the inferior clays and sands. 
Immediately upon the chalk at the bottom of all the ter¬ 
tiary strata in France there generally is a conglomerate or 
breccia of rolled and angular chalk-flints, cemented by sili¬ 
ceous 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 Gastornis 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.f 
That a formation so much explored for economical pur¬ 
poses as the Argile plastique around Paris, and the clays 
and sands of corresponding age near London, should never 
have aflbrded any vestige of a feathered biped previously to 
the year 1855, shows what diligent search and what skill in 
osteological interpretation are required before the existence 
of birds of remote ages can be established. 
Sables de Bracheux (C. 3, p. 252).-—The marine sands call¬ 
ed the Sables de Bracheux (a place near Beauvais), are con¬ 
sidered by M. Hebert to be older than the Lignites and 
Plastic clay, and to coincide in age with the Thanet Sands 
of England. At La Fere, in the Department of Aisne, in a 
deposit of this age, a fossil skull has been found of a quad¬ 
ruped called by Blainville Arctocyon primcevus^ and sup- 
* D’Archiac, Bulletin, tom. x.; and Prestwich, Quart. Geol. Journ., 1847, 
p. 377. 
t Quart. Geol. Journ., vol. xii., p. 204. 1856. 
