12 A Period in the History of our Planet. 



covcry, equally important to palaeontology and zoology; and not 

 the slightest doubt can exist that the discovered fossil is ac- 

 tually a bird. Only the last step is now wanting in order to 

 mount to the highest degree of vertebrated animals, and in the 

 epoch succeeding to the chalk this is done ; we meet with the 

 mammiferous animal in the strata of the tertiary formations.* 



Until Cuvier, the greatest naturalist of our times, and Alex- 

 ander Brongniart, directed their immortal labours into the field 

 of this formation, it was not properly distinguished from the 

 more recent alluvia. It was they who first, by an accurate com- 

 parison of its fossils, and especially those of the Paris basin, 

 made us circumstantially acquainted with the Fauna of this 

 formation. Their work still remains a model ; and Cuvier's 

 inquiries into fossil bones form the most exalted monument of 

 human acuteness in science. 



Some essential points bring the tertiary strata into the 

 closest connection with the circumstances to which the present 

 crust of the earth is subjected. Whilst the older formations, 

 upon whatever part of the earth they are met with, present a 

 surprising similarity in their Faunas, so that, apart from the 

 differences which the configuration of their outline must bring 

 along with it, the same remains are found in similar strata, in 

 either hemisphere indifferently ; and whilst, consequently, this 

 equality in the distribution of living creatures over the earth 

 indicates for the earliest epochs a more equal extension of tem- 

 perature, at the poles as at the equator, we find, on the other 

 hand, in the tertiary period, and perhaps even earlier, distinct 

 signs of the formation of different climates, impressing upon 

 different zones a different organic character. Yet this pecu- 

 liarity of climates is by no means so distinctly impressed upon 

 the proper tertiary formations, as in the diluvium or our pre- 

 sent epoch. The stratum still retains the same general zoolo- 

 gical character in all places where it is found, although con- 

 siderable modifications are perceived in the details. 



A second great step is the exact distinction which can bo 

 drawn in the tertiary period betwixt formations of the sea, of 



* The small mnrsupial nianimalia whicli Buckland discovered in the Jura for- 

 mation of kjtonesfield, still remain an isolated phenomenon. 



