Number of Animals in Geological Times. 359 



occurs at the present day ? So that it can be fairly said, that at 

 all periods fishes have presented as great a variety of forms, and 

 as numerous species, as under corresponding circumstances at 

 the present day. 



The class of Reptiles will allow similar conclusions ; for though 

 the giants of the class have chiefly been studied, do they not in- 

 dicate an abundance, and a variety of these animals during the 

 upper secondary formations as great as in any tropical region ? 

 and have we not sufficient indications among the tertiaries to be 

 justified in expecting that they also will turn out to be more 

 numerous than they are now known to be ? 



The class of Birds seems to form an exception in this view. 

 But there seems to be particular reason why the bones of birds 

 should be more liable to destruction and decomposition than 

 those of other Vertebrata. And whoever has traced the discoveries 

 made recently among the fossils of this class, will certainly not 

 insist upon a supposed scarcity of birds in former periods, but 

 rather be inclined to admit that the limited number now known 

 is to be ascribed to the deficiency of our knowledge rather than 

 to a want of these animals in earlier formations, indications of 

 their presence having been ascertained for several tertiary forma- 

 tions, for cretaceous deposits, and even for deposits belonging 

 to periods older than the chalk. 



Fossil Mammalia are comparatively too well known to call for 

 many remarks after what has been said above. Let us only 

 remember that the number of fossil species found in Brazil alone 

 equals the whole number of Mammalia known to live at present 

 in that country ; that the fossil Mammalia of New Holland com- 

 pare already favourably with the living species of that continent ; 

 and that the locality of Montmartre alone has yielded as many 

 large Mammalia as occur all over Europe, and the Mauvaises 

 Terres in Nebraska as many as may be found in North America 

 now. So that, if we grant simply that among Vertebrata the 

 diversity has been increasing with the successive introduction of 

 their different classes, the number and diversity of these differ- 

 ent classes at each period have been as great as they are at 

 present. 



These facts are of the utmost importance with reference to the 

 great question of the order of succession and gradation of animals 

 in the .different geological periods. They cut away for ever one 

 of the arguments upon which the assertors of the development 

 theory have insisted most emphatically. Before it could be 

 granted that the great variety of types which occur at any later 

 period has arisen from a successive differentiation of a few still 

 earlier types, it should be shown that in reality in former periods 

 the types are fewer and less diversified ; and we have now shown 



