34 Bulletin 15 344 



5 



4 



3 



Tongrian. 2 



Friable limestone of Agen. 

 Limestone charadlerized by Asterias. 

 Clays with Ostrea lojigirostris and O. cyatJnda. 

 Freshwater limestone of Castillon and Civrac. 

 Friable sandstone of Fronsac and clays with Liin- 

 n(za and Planorbis. 



Sandstone of Fronsac. The friable sandstone of Fronsac 

 varies from a loose sandstone to sandj^ clays, greenish and more 

 or less micaceous. The formation which is typical at Fronsac 

 extends along the valley of the Dordogne and of the Dronne, and 

 is developed principally to the north of Coutras. 



Occasionally there is no trace of underlying Eocene, and the 

 sandstone then rests* direcftly upon the Cretaceous as at La Clotte. 

 At Fronsac, however, the sandstone overlies clays which contain 

 Limncea, Planorbis and Melanopsis mansiana, a species found in 

 clays above the gypsum in the Paris basin at Pantin. Hence M. 

 Vasseur has coordinated these beds. 



The sandstone of Fronsac is, in general, unfossiliferous. 

 The only fragments which can be identified are those of turtles of 

 the genus Trionyx, and of the large vertebrate Paleothej^ium 

 girondicuni, both forms indicating the lake origin of the sand- 

 stone. 



Limestone of Castillo7i a?id Civrac. The freshwater limestone 

 of Castillon and Civrac is irregularly developed. Ou the right 

 bank of the Garonne it is important only to the eastward of St. 

 Emilion, as far as Castillotl. Along the Dordogne, the limestone 

 also developes to the eastward, and, at Saint-Foy-la-Grande, 

 reaches a depth of 20 metres. 



On the left bank of the Gironde, this formation is especially 

 well developed in Medoc, near the town of Civrac. It appears 

 again, though in an argillaceous form, at Vertheuil.f Saint- 

 Sauveur, Blanquefort and other localities. 



* Poller et Vasseur, Sur les formations infratongriennes du Bassin de la 

 Gironde, Sac. Lin. de Bord. C. R. des Seances, 18 Juillet, 1888. 



t Benoist, E., Description Geologique et Paleontologique des communes 

 de Saint-Estephe et de Vertheuil, Ext'rait des ASles de la Soc. Lin. de Bor- 

 deaux, t. 39. 



