232 MIOCENE OF BORDEAUX. [Ch. XIV. 



there is a remarkable continuity in the succession of strata, the upper- 

 most being somewhat newer than the faluns of Touraine and the low- 

 est somewhat older than the Fontainebleau sandstone already alluded 

 to. In the highest group, that of Salles, in which Voluta Lamberti 

 and Cardita Jouanneti occur, there are many fossils common to the 

 Pliocene or Subapennine strata. Next below these are the faluns 

 proper of Bordeaux, which include the faluns of Saucats and Leognan 

 and those of Dax in the adjoining basin of the Adour. These forma- 

 tions, which contain among other shells Pecten Burdigalensis and 

 Ancillaria glandiformis, coincide in age with the faluns of Touraine ; 

 but so many of the species are peculiar to the south as to imply that 

 there was a separation by a considerable tract of land between the 

 basins of the Loire and Gironde. 



Strata which may be referred to the Lower Miocene come next in 

 the descending order, comprising those of Merignac and Bazas, the 

 first blackish and the latter of marine origin. In this fiuvio-marine 

 series, Cerithium plicatum (fig. 173, p. 240), C. margaritaceum, C. 

 Brongniarti, &c, and in the marine beds Pyrula Lainei occur. The 

 greater part of this series is considered by M. Tournouer to correspond 

 in age with the freshwater limestone of La Beauce in the basins of the 

 Loire and Seine. 



Still lower is the Asterias limestone, which with its overlying marls 

 is about 300 feet in thickness, in which Cerithium plicatum and C. 

 margaritaceum are again met with, together with JVatica crassatina 

 and other shells characteristic of the Etampes and Fontainebleau sands 

 before mentioned. In these lower strata are many species common to 

 the Parisian Eocene system, to the Calcaire Grossier for example, and 

 even beds still lower. There are also several species of nummulites in 

 the Asterias limestone, and their presence marks a difference in the 

 character of the Lower Miocene of the South of Europe, as con- 

 trasted with that of the North. These and other indications of a 

 passage from an older to a newer group, is just what we might expect 

 in proportion as our series of monuments begins to be more and 

 more complete. According to M. Tournouer, the Lower Miocene 

 shells identifiable with Eocene species are always varieties of the 

 same — an important fact as bearing on theories of the origin of 

 species* Below the whole of these formations lies a true Eocene lime- 

 stone called the Calcaire de Blaye, of the age of the Calcaire Grossier 

 of the Paris basin. In order to explain the succession of beds in the 

 basin of the Gironde, several oscillations of level are necessary. 

 The same wide area was alternately converted into sea and land and 

 into brackish-water lagoons, and finally into freshwater ponds and 

 lakes. 



Upper Miocene strata of Gers. — Among the freshwater strata last 

 alluded to near the base of the Pyrenees, are many of Upper Miocene 

 age, from which bones of the Dinotherium giganteum and entire skel- 

 etons of the Mastodon angustidens have been obtained by M. Lartet. 







