220 MIOCENE PERIOD. [Ch. XVI. 



manner as we now find small lakes scattered over our con- 

 tinents and islands wherein deposits are forming, quite de- 

 tached from all contemporary marine strata. To determine 

 the age of such groups with reference to the great chronolo- 

 gical series established for the marine strata, must often be a 

 matter of difficulty, since we cannot always enjoy an oppor- 

 tunity of studying a locality where the fresh- water species are 

 intermixed with marine shells, or where they occur in beds 

 alternating with marine strata. 



The deposit of the Upper Val d'Arno before alluded to, 

 (p. 161) was evidently formed in an ancient lake ; but although 

 the fossil testaceous and mammiferous remains preserved 

 therein are very numerous, it is scarcely possible, at present, 

 to decide with certainty the precise era to which they belong. 

 I collected six species of lacustrine shells, in an excellent 

 state of preservation, from this basin belonging to the genera 

 Anodon, Paludina and Neritina; but M. Deshayes was unable 

 to identify them with any recent or fossil species known 

 to him. If the beds belonged to the older Pliocene forma- 

 tions we might expect that several of the fossils would agree 

 specifically with living testacea ; and we are therefore disposed 

 to believe that they belong to an older epoch. If we consider 

 the terrestrial mammalia of the same beds, we immediately 

 perceive that they cannot be assimilated to the Eocene type, 

 as exhibited in the Paris basin, or in Auvergne and Velay : 

 but some of them agree with Miocene species. Mr. Pentland 

 has obligingly sent me the following list of the fossil mammifers 

 of the Upper Val d'Arno which arc in the museums of 



Paris. Fvra. Ursus cultridens, Viverra Yaldarnensis, Canis 



lupus, and another of the size of the common fox. Hyaena 

 radiata, II. fossilis. Felis (a new species of the size of the 

 panther). Hodentia. Histrix, nearly allied to dorsalis, Castor. 

 Pacfiijdannatn. Elephas Italicus, Mastodon angustidens, M. 



Taperoides, Tapir , Equus , Sus scrofa, llhinoceros 



leptorhinus, Hippopotamus major, fossilis. Ruminantia. 



