AFFINITIES OF EXTINCT SPECIES 383 



as unequal intervals of time have elapsed between consecM- 

 tive 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 in- 

 stance, the species of mastodons and elephants, when ar- 

 ranged by Dr. Falconer in two series, — in the first place 

 according to their mutual affinities, and in the second place 

 according to their periods of existence, — do not accord in 

 arrangement. The species extreme in character are not the 

 oldest or the most recent; nor are those which are interme- 

 diate in character, intermediate in age. But supposing for 

 an instant, in this and other such cases, that the record of 

 the first appearance and disappearance of the species was 

 complete, which is far from the case, we have no reason to 

 believe that forms successively produced necessarily endure 

 for corresponding lengths of time. A very ancient form 

 may occasionally have lasted much longer than a form else- 

 where subsequently produced, especially in the case of terres- 

 trial productions inhabiting separated districts. To compare 

 small things with great; if the principal living and extinct 

 races of the domestic pigeon were arranged in serial affinity, 

 this arrangement would not closely accord with the order in 

 time of their production, and even less with the order of 

 their disappearance; for the parent, rock-pigeon still 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 back originated earlier than 

 short-beaked tumblers, which are at the opposite end of the 

 series in this respect. 



Closely connected with the statement, that the organic re- 

 mains 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 each other, than are the fos- 

 sils from two remote formations. Pictet gives as a well- 

 known instance, the general resemblance of the organic re- 

 mains from the several stages of the Chalk formation, 

 though the species arc distinct in each stage. This fact 



