172 GEOLOGICAL DISTRIBUTION. 



is here a geological break. Only there where the continuity of the 

 geological system is complete, or where the imperfection of the 

 record is reduced to insignificance, can we hope to meet with an 

 organic chain who§e continuity is likewise complete. No such 

 complete record, or anything approaching it, has as yet been dis- 

 covered, nor is it at all likely that one will ever be discovered. But 

 the gaps in the record that occur in one locality or country may 

 be wanting in another, those present here be absent in the third, 

 and so on ; hence, by a series of comparisons made between several 

 localities, we can in a measure realise a comparatively perfect 

 record, or at any rate one in which the breaks have been materially 

 narrowed, and with it also a comparatively perfect organic chain. 

 Except possibly in one or two regions of the earth's surface. New 

 Zealand and California, nothing that may be said absolutely to 

 link together the Cretaceous and Tertiary deposits, at least those 

 of the marine series, has as yet come to light; the faunas are 

 largely distinct, and their distinctness is the index of the inter- 

 val that separates the outgoing of the one and the incoming of the 

 other. 



The Tertiary fauna presents to us a clearly modern aspect, and 

 one that characterises all the animal groups represented, from the 

 lowest to the highest. And the farther we advance in this period 

 the more modern becomes the general faunal facies, so that in the 

 Pliocene, or uppermost division, not only are the genera largely 

 identical with existing ones, but (if we exclude the vertebrates) 

 also the species, notably among the mollusks. It may be stated 

 in a general way that all the more comprehensive of the animal 

 groups now existing are represented in the Tertiary deposits, and 

 the majority of these date from the Eocene, or earliest division. We 

 have no longer representatives of those wonderful reptilian orders, the 

 Ichthyosauria, Dinosauria, Pythonomorpha, and Pterosauria, which 

 characterised the greater portion of the Mesozoic era, and continued 

 to its termination; nor do we find any vestiges of the scarcely less 

 wonderful birds of the odontornithic group,* or of the type rep- 

 resented by Archaeopteryx. Both reptiles and birds belong to 



* An exception may, perhaps, "be made in favour of the Odontopteryx, de- 

 scribed by Professor Owen, which has the substance of both jaws developed into 

 well-pronounced seiTations (or false teeth), an exaggeration of the character 

 exhibited by ducks and geese, to which the bird appears to have been related. 



