G. F. Harris — Geology of the Gironde. 25 



English Upper Eocene mollusca are being identified, I fancy very 

 few would give more than the most superficial glance at works on 

 fossils called (under the old nomenclature) Miocene, and yet on the 

 transference of portions of these latter to the Lower Oligocene, we 

 are presented with a fauna of the same age as our Headon beds. 

 I was very much struck with the close resemblance of several 

 species of the Oligocene mollusca in the Bordelais with those of the 

 Oligocene beds of the Isle of Wight, and I believe many of them 

 are specifically identical, whilst others certainly ought not to rank 

 higher than " varieties," though the mollusca referred to are now 

 regarded as entirely distinct species. On the present occasion, 

 however, I do not propose to go further into this matter. 



The Oligocene beds of the Gironde are divided into two etages, 

 the Tongrien and the Aquitanien. 



The Tongrien is subdivided into four parts : 



1. Lower mollasse of Agenais. 3. Lacustrine limestone of Castillon. 



2. Asterias limestone. 4. Mollasse of the Fronsadais. 



No. 4 is, generally, a greenish sandy clay without fossils. At 

 Fronsac certain beds under this have been called (i infra-mollas- 

 siqnes" by MM. Fallot et Croizier. 1 It is difficult to give the 

 precise age of these and of several other beds found on about the 

 same horizon in certain parts of the Department ; but according to 

 the views of the former observer, they constitute a passage between 

 the Eocene and Oligocene. 



No. 3 is not very persistent in character. In the typical locality 

 it is a white limestone with flints, containing fresh-water mollusca, 

 which seem to indicate that it is approximately of the age of the 

 " Calcaire cle Brie" of the Paris basin. 



No. 2 is also known as the Botirg or Saint-Macaire limestone, 

 and is the most typically developed Tongrien bed in the district. 

 The lower part, well developed near Libourne, contains Ostrea 

 cyathula and 0. longirostris. The upper or true Asterias limestone 

 forms the hills between Roque-de-Tau and Bourg, the high ground 

 bordering the Dordogne, and, generally, the south-eastern and 

 central portion of the Department, and in certain places from 

 Pauillac to Vendais, between the western bank of the Garonne 

 and the sea. Characteristic fossils are Trochus labarum, Nalica 

 (Ampullina) crassatina, Pectunculus angusticostatus, Delphinula 

 scobina and Lucina Delbosi. The general facies, M. Fallot says, 3 

 is that of the " Sables de Fontainebleau " of the Paris basin. 



No. 1 is a green or yellow clay with calcareous concretions ; in 

 some localities the beds are more or less sandy, but interesting on 

 account of the occurrence in them of Authracotherium, Rhinoceros, 

 and other mammals. 



The higher subdivision of the Oligocene — the Aquitanien— is 

 generally split up into three assises : — 



1. Upper. — Grey limestone of Agenais. 



2. Middle. — Bazas sandstone, and middle mollasse of Agenais. 



3. Lower. — White limestone of Agenais. 



The Aquitanien beds crop out principally in the south-east of the 



1 Actes Soc. Lin. de Bordeaux, tome xl. p. 55. 



2 " Esquisse Geol. du Dept. de la Gironde," 1889, p. 10. 



