60 TERTIARY MAMMIFEROUS REMAINS. [Qh. 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. 



