60 
TERTIARY MAMMIFEROUS REMAINS. 
[Ch. V. 
In the Miocene mammalia we find a few of the generic forms 
most frequent in the Eocene strata associated with some of 
those now existing, and in the Pliocene we find an intermixture 
of extinct and recent species of quadrupeds. There is, there- 
fore, a considerable degree of accordance between the results 
deducible from an examination of the fossil testacea, and those 
derived from the mammiferous fossils. But although the latter 
are more important in respect to the unequivocal evidence 
afforded by them of the extinction of species, yet, for reasons 
before explained, they are of comparatively small value in the 
general classification of strata in Geology. 
It will appear evident, from what we have said in the last 
volume respecting the fossilization of terrestrial, species, that 
the imbedding of their remains depends on rare casualties, and 
that they are, for the most part, preserved in detached allu- 
vions covering the emerged land, or in osseous breccias and 
stalagmites formed in caverns and fissures, or in isolated lacus- 
trine formations. These fissures and caves may sometimes 
remain open during successive geological periods, and the allu- 
vions, spread over the surface, may be disturbed, again and 
again, until the mammalia of successive epochs are mingled 
and confounded together. Hence we must be careful, when 
we endeavour to refer the remains of mammalia to certain ter- 
tiary periods, that we ascertain, not only their association with 
testacea of which the date is known, but, also, that the remains 
were intermixed in such a manner as to leave no doubt of the 
former coexistence of the species. 
In the next page will be found a Synoptical Table of the 
Recent and Tertiary formations alluded to in this chapter. 
N.B. By aid of this table, the reader will be able to refer 
almost all the localities of the Pliocene formations enumerated 
in the Tables of M. Deshayes (Appendix I.) to the newer or 
older division of the Pliocene period established in the fore- 
going chapter. 
