300 ON THE ORIGIN OF SPECIES 



those of the overlying carboniferous, and underlying 

 Silurian system. But each fauna is not necessarily 

 exactly intermediate, as unequal intervals of time have 

 elapsed between consecutive formations. 



It is no real objection to the truth of the statement, 

 that the fauna of each period as a whole is nearly 

 intermediate in character between the preceding and 

 succeeding faunas, that certain genera offer exceptions 

 to the rule. For instance, mastodons and elephants, 

 when arranged by Dr. Falconer in two series, first 

 according to their mutual affinities and then according 

 to their periods of existence, do not accord in arrange- 

 ment. The species extreme in character are not the 

 oldest, or the most recent ; nor are those which are 

 intermediate in character, intermediate in age. But 

 supposing for an instant, in this and other such cases, 

 that the record of the first appearance and disappear- 

 ance of the species was perfect, we have no reason to 

 believe that forms successively produced necessarily 

 endure for corresponding lengths of time : a very 

 ancient form might occasionally last much longer than 

 a form elsewhere subsequently produced, especially in 

 the case of terrestrial productions inhabiting separated 

 districts. To compare small things with great : if the 

 principal living and extinct races of the domestic 

 pigeon were arranged as well as they could be in 

 serial affinity, this arrangement would not closely 

 accord with the order in time of their production, 

 and still less with the order of their disappearance ; 

 for the parent rock - pigeon now lives ; and many 

 varieties between the rock-pigeon and the carrier have 

 become extinct ; and carriers which are extreme in 

 the important character of length of beak originated 

 earlier than short-beaked tumblers, which are at the 

 opposite end of the series in this same respect. 



Closely connected with the statement, that the 

 organic remains from an intermediate formation are 

 in some degree intermediate in character, is the fact, 

 insisted on by all palaeontologists, that fossils from two 

 consecutive formations are far more closely related to 



