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 j 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 are in the museums of 
Paris. Feres.— Ursus cultridens, Viverra Valdarnensis, Canis 
lupus, and another of the size of the common fox. Hyaena 
radiata, H. fossilis. Pelis (a new species of the size of the 
panther). Rodentia. — Histrix, nearly allied to dorsalis, Castor. 
Pachydermata. — Elephas Italicus, Mastodon angustidens, M. 
Taperoides, Tapir Equus , Sus scrofa, Rhinoceros 
leptorhinus, Hippopotamus major, fossilis. Ruminantia,— 
