INTRODUCTION. 9? 



other influential causes.* But, before we proceed 

 further with the orders of mammalia, it may be 

 proper to take a slight review of the organic remains 

 of this class, which attest former zoological eras, 

 apparently terminated, by mighty convulsions of the 

 earth, totally or partially, according to the evidence 

 of different epochs, and replaced by a new creation, 

 not based upon organisations different in principle 

 from the former, but almost universally distinct in 

 species, often in genera, and sometimes apparently 

 in the whole order. The widest differences appear 

 to belong to the remotest periods, and approxima- 

 tions gradually assimilating with the present zoo- 

 logy, increasing as the epochs are comparatively 

 recent. 



Thus, the first traces of mammalia occur in 

 the lower oolite series (the Oxford), where mar- 

 supial remains have been detected. Excepting some 

 doubtful cetacean, no others have been observed of 

 a later period, until the lower tertiary deposit is 

 examined. This is now commonly called the eocine 

 period, as observed in the London and Paris basins : 

 it contains many genera of now extinct forms of 

 quadrumana, cheiroptera, rodentia, and marsupialia; 

 but it is chiefly in the numerous pachydermata 

 that it abounds, while carnivora seem to have been 

 wanting, their office being supplied by huge sau- 



* In a future work, we may revert to the history of man, 

 and trace the existing races from their most ancient locations, 

 by the routes which geographical necessity must have imposed, 

 to reach their later and present habitations. 



6 



