642 CLASSIFICATION OF MIOCENE 



writings on the fossils of the Mayence Basin, has lately pointed out 

 several connecting links between the beds commonly called Lower 

 Miocene and the overlying formations coeval with the faluns of Tou- 

 raine. M. Raulin, also, in a paper just printed on the faluns of the Gi- 

 ronde,* has given the names of Middle and Lower Miocene to the 

 equivalents of the Fontainebleau and Limburg beds, or to Professor 

 Beyrich's " Oligocene" strata, the faluns of Touraine being classed as 

 " Upper Miocene." 



M. Hebert published, in 1855, a map descriptive of the areas of two 

 tertiary seas, which succeeded each other in the Paris Basin, — the first 

 that of the Calcaire grossier, and the second, that of the Fontainebleau 

 Sands, — showing how marked is the want of coincidence between them • 

 a fact which implies the occurrence of great geographical changes in 

 the interval of time between the two eras compared. In the explana- 

 tion of his map he gives his reasons for regarding the zone of Cerithium 

 plicatum, or that of the Fontainebleau Sands, as the most convenient 

 line of demarcation between Lower and Middle tertiary, or between 

 Eocene and Miocene.f M. Lartet, also a distinguished French osteolo- 

 gist, whose writings on fossil mammalia are so well known, has favored 

 me with his valuable counsel on this controverted subject ; observing, 

 that although the fossil testacea of the Fontainebleau Sands show a 

 preponderance of affinities towards an Eocene fauna, and small connec- 

 tion with the faluns of Touraine, yet, on the other hand, the freshwater 

 "Calcaire de la Beauce," immediately overlying the Fontainebleau 

 Sands, and other lacustrine formations in Auvergne and Central France, 

 as well as the Mayence Basin, cannot be included in the same Eocene 

 system without doing violence to paleontological principles. The group- 

 ing of the fossil mammalia, he remarks, becomes less natural by such an 

 arrangement; for not only many genera, but even some species, are 

 found on both sides of the arbitrary line of demarcation thus drawn 

 between Eocene and Miocene. The genera Dorcatherium, Cainotherium, 

 Anchitherium, and Titanomys, for example, and Rhinoceros incisivus 

 and others, are made common to Eocene and Miocene. 



Professor Forbes, in his posthumous memoir on a tertiary formation 

 of fiuvio-marine origin in the Isle of "Wight, J has observed, that there 

 are certain bands of well-marked fossils so widely extended as to indi- 

 cate definite horizons ; and of these perhaps the most constant is " the 

 zone of Cerithium plicatum" well-marked among the Tertiaries of 

 France, Belgium, and Germany, and equally so in the Isle of Wight. 

 Referring then to the connection between this zone and the underlying 

 formations, he continues : " There is evidently no break in this part of 

 the series of Tertiary depositions, and it would be harsh and forced to 

 place one portion in the Eocene, and another in the Miocene, as has 

 been done by continental geologists. In the Isle of Wight we have 



° Actes de l'Academie de Bordeaux, 1855. 



f Bulletin, 1855, torn. xii. p. 760. 



% Mem. Geol. Survey, London, 1856, p. 99. 



