CHAP. XI.] AFFINITIES OF EXTIXCT SPECIES. 287 



between the successive formations. Subject to these allowances, 

 the fauna of each geological period undoubtedly is intermediate 

 in character, between the preceding and succeeding faunas. I 

 need give only one instance, namely, the manner in which the 

 fossils of the Devonian system, when this system was first dis- 

 covered, were at once recognised by palaeontologists as intermediate 

 in character between those of the overlying carboniferous, and 

 underlying Silurian systems. 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, the species of masto- 

 dons and elephants, when arranged 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 intermediate 

 in character, intermediate in age. But supposing for an instant, 

 in this and other such cases, that the record of the first appear- 

 ance 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 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 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 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 each other, than are the fossils from two remote 

 formations. Pictet gives as a well-known instance, the general 

 resemblance of the organic remains from the several stages of the 

 Chalk formation, though the species are distinct in each stage. 

 This fact alone, from its generality, seems to have shaken Pro- 



