ITKANOl]. 
213 
division witli estuarine shells, such as Potamides, Melanopsis, 
and Gongeria. The total thickness of the Plaisancian may reach 
as much as 200 or 250 metres. 
In the neighbourhood of Montpellier, where I had an oppor¬ 
tunity of examining the beds, the lower portion of this group 
consists of sands with thick banks of Oysters {Ostrea cucullata), 
and numerous bones of land and marine mammals. The 
abundance of bones of Sireuia iHalitherium Serresii) is very 
striking. Overlying the marine sands are sandy marls with 
brackish-water shells, as is usually the case in the south of 
France.* 
On examining the Plaisancian fauna of the south of France, 
one is at once struck by the great difference of the mollusca from 
the nortli European assemblage, though the strata are apparently 
of the same age. To attempt any comparison between them is 
useless, the conditions and climate under which they respectively 
lived were so different. It is interesting, however, to notice 
that the temperature of the Mediterranean during the Plaisancian 
period seems to have been nearly as much above that of the 
existing Mediterranean, as the temperature of the Coralline Crag 
sea was above that of the seas that now wash the English coasts. 
The isotherms were probably as far apart then as now, but each 
was considerably south of its present position. 
The Plaisancian deposits of Montpellier have yielded a con¬ 
siderable number of land mammals, of which Dr. Viguier has 
supplied a list of 15 species. The corres})onding strata in the 
north of Europe, unfortunately have furnished very few of which 
the true horizon can be fixed. We have only the derivative 
fossils at the base of the Red Crag for purposes of comparison. 
A mastodon, a tapir, and a rhinoceros are probably common to 
Montpellier and Suffolk, the other mammals seem to be different. 
Here again no exact correlation is possible at present. 
As we travel eastward, both the Plaisancian and the Astian 
become thoroughly marine, changing to strata of the Sub-Apen- 
nine type as we enter Italy. It is not, however, till the eastern 
side of the Gulf of Genoa is reached that the Pliocene strata 
expand into the-wide thick sheet, lying between the Apennines 
and the sea, which led to the adoption of the term Sub-Apen- 
nine ” for the whole group. 
Sub-Apennine strata cover enormous areas in Italy and Sicily, 
rising into low hills on each side of the Apennine chain. They 
have been little affected by the disturbance associated with the 
formation of these mountains. The Pliocene deposits sometimes 
rest conformably on, and pass down into, the Miocene; more 
commonly they abut against the disturbed rocks of the 
Apennines. 
In Piedmont Tertiary rocks are largely developed, and as the 
relations of the deposits have recently been carefully worked out 
* Viguier, Pliocene de Montpellier. Comptes Eendus, vol. cvi., p. 14,263. (1888.) 
Bull. Soc. Geol. France^ ser. 3, vol. xvii., p. 379. (1889.) 
