CHAPTER XVIII. 



Marine formations of the Eocene period Strata of the Paris basin 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 basin Observations of M. C. 

 Prevost Sketch of the different subdivisions of the Paris basin 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 

 ' 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 



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