ITS CHARACTERISTICS. 153 



tenanted the plain and roamed the forest, and of the ptero- 

 saurs that winged the air, not a living trace remains. They 

 are utterly extinguished, and their place is now filled by 

 the crocodiles, lizards, turtles, and serpents of existing na- 

 ture. The birds so scantily preserved (though largely indi- 

 cated) in mesozoic strata, and the mammals represented 

 only by a few insignificant marsupials, now assume the 

 chief importance in the great vital scheme ; and last, and 

 highest of all, man himself enters on the stage of being as 

 the crowning form of the current epoch. 



To facilitate comparison, it is usual to subdivide the 

 Cainozoic into eocene, miocene, pliocene, and pleistocene 

 that is, into its earliest, less recent, more recent, and most 

 recent life-stages j but enough for our review to treat it in 

 two great sections the first, when land and sea had a 

 somewhat different distribution from the present ; and the 

 second, when they had assumed, within the limits of an 

 appreciable mutation, their existing arrangement. Adopt- 

 ing the familiar phraseology that designates the palae- 

 ozoic as primarily and the mesozoic as secondary, we may 

 regard the first section as tertiary, and the second as post- 

 tertiary ever bearing in mind that such distinctions are 

 mere provisional aids to facilitate the comprehension of 

 geological progression. It has been customary, no doubt, 

 for certain geologists, generalising from limited tracts in 

 Europe, to draw a bold line of demarcation between the 

 chalk and tertiary so bold that not a single species was 

 regarded as passing from the one epoch to the other. This, 

 like many of the early conclusions of the science, is alto- 

 gether erroneous ; and now, even in Europe, to say nothing 

 of America, abundant passage -beds have been detected, 

 showing in this instance, as in every other, that abrupt 

 transitions are at the most merely local and limited pheno- 



