32 Bulletin 15 342 



however, in 1868,* recog'nised the true position of this limestone 

 as of the same age as the sands of Fontainebleau. In 1872,! he 

 obtained further evidence from a study of the fauna in more de- 

 tail. This revealed the presence of Natica crassatina, N. augus- 

 tata, Turbo Parkinsani, Cerithium plicatum, C. trochleare and Cy- 

 therea incrassata, which proved beyond question the corredlness 

 of his earlier conclusion. Vasseur,J after a comparative study ^ 

 in 1881, confirmed the views of Tournouer. 



The limestone of Rennes is especially characfterized by Fora- 

 minifera of the genus Archiaci7ta. Other fossils are rare and are 

 found only as casts. 



Freshwater limestone and clays. The upper layers of the 

 limestone are brackish and freshwater deposits, with a fauna com- 

 prising species of Potainides, associated with Planorbis and Limncza. 

 These layers are overlaid by clays of freshwater origin containing: 

 Potamides Lamarcki, Cyclostoma antiquurn and Palude&trina Dic- 

 buissoni. 



The freshwater limestone and clays of Rennes represent the 

 Beauce limestone of the Paris basin. 



Relatio7i of the Rennes fauna to that of Bordeaux. The 

 marine fauna of Rennes has been found to be more closely related 

 to that of Bordeaux than to that of the neighboring Parisian 

 basin. It has also very few species in common with the Belgian 

 Oligocene. But the presence in the Rennes basin of Natica an- 

 gustata. Turbo Parkinsoni, I^izvicardiuni aquitaniaim and other 

 species which are common in the Gironde valley, and total 

 strangers in the basins of northern Kurope, has suggested the 

 connecftion of the Rennes basin, by way of Nantes, with that of 

 Bordeaux. 



Oligoceiie in southwestern France. The Oligocene in south- 

 western France outcrops in the valleys of the Gironde and the 

 Adour. 



^ Bjill. Soc. Giol. de France, 2emeser., t. XXV, p. 367, 186S. 

 ^Ibid., t. XXIX, p. 4S1, 1S72. 



X Recherches geoL sur les terrains tertiaires de la France occidentale,, 

 Paris, 1 88 1. 



