MAMMALIA OF PLIOCENE PERIODS. 93 
the tropical character of many other animals, 
even of the latest tertiary strata, in favour of the 
opinion, that the climate of Europe maintained 
a high, though probably a gradually decreasing 
temperature, even to the latest period of the 
tertiary formations. 
We have many sources of evidence whereby 
the history of the Pliocene periods is illustrated : 
First, we have the remains of terrestrial animals, 
drifted into estuaries or seas, and preserved 
together with marine shells ; such are the Sub- 
apennine marine formations, containing the re- 
mains of Elephant, Rhinoceros, &c. and the 
Crag of Norfolk.* 
Secondly, we have similar remains of terres- 
trial quadrupeds, mixed, with fresh- water shells, 
in strata formed during the same epoch, at the 
bottom of fresh-water lakes and ponds ; such as 
those which occur in the Val D'Arno, and in the 
small lacustrine deposit at North Cliff, near 
Market Weighton, in Yorkshire. (See Phil. 
Mag. 1829, vol. vi. p. 225.) 
Thirdly, we have remains of the same animals 
* In the museum at Milan, I have seen a large part of the 
skeleton of a Rhinoceros, from the Sub-apennine formation, 
having oyster shells attached to many of its bones, in such a 
manner as to show that the skeleton must have remained undis- 
turbed for a considerable time at the bottom of the sea. Cuvier 
also states that in the museum at Turin there is the head of an 
elephant, to which shells of the same kind similarly attached, 
and fitted to the form of the bones. 
