CHAPTER XVIII. 
Marine formations of the Eocene period — Strata of the Paris hasin how far 
analogous to the lacustrine deposits of Central France — Geographical connexion 
of the Limagne d'Auvergne and the Paris basin — Chain of lakes in the Eocene 
period — Classification of groups in the Paris hasin — Observations of M. C. 
Prevost — Sketch of the different subdivisions of the Paris hasin — Contem- 
poraneous marine and fresh-water strata — Abundance of Cerithia in the 
Calcaire grossier- — Upper marine formation indicates a subsidence — Part of 
the Calcaire grossier destroyed when the upper marine strata originated — 
All the Parisian groups belong to one great epoch — Microscopic shells- 
Bones of quadrupeds in gypsum — In what manner entombed — Number of 
species — All extinct — Strata with and without organic remains alternating — 
Our knowledge of the physical geography, fauna, and flora of the Eocene period 
considerable — Concluding remarks. 
EOCENE FORMATIONS— PARIS BASIN. 
The geologist who has studied the lacustrine formations de- 
scribed in the last chapter cannot enter the tract usually termed 
1 the Paris Basin ' without immediately recognizing a great 
variety of rocks with which his eye has already become fami- 
liar. The green and white marls of Auvergne, Cantal, and 
Velay, again present themselves^ together with limestones and 
quartzose grits, siliceous and gypseous marls, nodules and 
layers of flint, and saccharoid gypsum ; lastly, in addition to all 
this identity of mineral character, we find an assemblage of the 
same species of fossil animals and plants. 
When we consider the geographical proximity of the two 
districts, we are the more prepared to ascribe this correspond- 
ence in the mineral composition of these groups to a combina- 
tion of similar circumstances in the same era. From the map 
(No. 56, p. 226) in the last chapter, it will be seen that the 
united waters of the Allier and Loire, after descending from 
the valleys occupied by the fresh-water formations of Central 
France, flow on till they reach the southern extremity of what 
is called the Paris basin. M. Omalius d'Halloy long ago 
Voi, III. R 
