337 The Oligocene of the Southern United StatEvS 27 



10. White clays. Limncea strigosa. 



9. Blue clays. 



Clays above 8. Gypsum (ist bed). Vertebrate fauna. PalcB- 

 the gypsum. other mm. 



7. Yellow clays. 



6. G3'psum (2nd bed). Only Eocene species. 



5. Marls. Lucina inoniata. 



4. Gypsum (3rd bed). A few Oligocene species. 



3. Yellow clays. Pholadomya liidensis. 



Gypsum. 2. Gypsum (4th bed). Fauna resembling Eo- 

 cene. 



I. Green sands of Argenteuil. 



Base of the Oligocene series. The basal beds of the Oligocene 

 in the Paris basin are not definitel}' determined. This is due to 

 the lack of unconformity, the scarcity of well preserved fossils in 

 the gypsum beds and the contradicftory evidence given by the 

 species which occur. Thus the fourth bed contains species closely 

 resembling those from the Eocene (sables moyens). The third bed 

 has mostly Eocene species, but contains also a few new, Oligocene 

 types. The second bed is nearly unfossiliferous, but what species 

 there are, are Eocene. The first bed is characflerized by verte- 

 brate remains, especially those of PalcEotherium. Eapparent con- 

 siders that the Oligocene series begins with the blue clays which 

 rest on the first gypsum bed. Cossman and Lambert include the 

 gypsum in the Oligocene. Others claim that the green clays 

 characterized b}' Cyrena are the true base of the series. 



Clays above the gypsum. The clays above the gypsum are 

 lake deposits. The principal species are Planorbis pianulatiis, 

 LimncEa strigosa and Nystia plicata. These clays are well devel- 

 oped at Pantin, near Paris, and extend east to Chateau-Thierry. 



The green clays. The green clays, four or five metres thick, 

 overlie the white clays and contain a brackish and marine fauna. 

 These beds at the base are very foliaceous, yellowish and charac- 

 terized by Cyrena convexa. Above, the clays become bluish, and, 

 in some localities, are rich in Cerithiiim plicatum, C. trochleare and 

 Psammobia plana. The highest layers are green, and often con- 



