78 General Part. 



They belong, however, witliout exception, to different genera and 

 species, often, also, to families and orders not occurring in this age, 

 and, moreover, large divisions, forming the most conspicuous part of the 

 present fauna, did not then exist. So, for instance, the Vertebrata, 

 from the oldest formation to the Devonian, are represented only by 

 Fish, whilst Amphibia, Reptiles, Birds and Mammals are entirely 

 wanting. From what has been said above it will be seen that these 

 observations must be interpreted with great caution, for the absence 

 of certain animals from a given formation does not necessarily mean 

 that they did not live in that period. This much, however, can 

 be said : had the group been largely represented in that early time, 

 some remains at least would probably have been found. The nearer 

 the period in which the formation was laid down to the present day, 

 the more closely does the fauna resemble that now existing. 



This agrees with what must be expected on the theory of 

 descent. An opinion is expressed by the opponents of this 

 theory that, were it correct, the contents of the strata should fur- 

 nish a far more complete phylogeny : and they say further that 

 there is, even in the oldest fossiliferous formation, the Cambrian, a 

 small fauna, which, though poor, is still far more specialised than 

 the original fauna could be, according to this hypothesis. The 

 first objection is already disposed of by the foregoing remarks, 

 from which it is evident that our knowledge of primaeval times must 

 necessarily be extremely incomplete ; and as for the second 

 objection, it must be pointed out that the oldest known animals 

 are not necessarily the earliest to have existed ; it is quite possible that 

 they had a long line of unknown ancestors. Geology can show below 

 this formation others still older, which probably were also formed 

 under water, but were so modified (metamorphosed) in course of time 

 that it would not be extraordinary if the then existing fauna, which 

 may have consisted chiefly of soft forms, had left no trace.* 



When the appearance, in course of time, of individual groups is 

 observed, a similar impression of the small number of facts against 

 the doctrine of descent, is gained. This is, for example, the case with 

 the classes of the Vertebrata : if a Vertebrate pedigree based on a 

 consideration of the structure of the different Vertebrate groups is 

 designed, Amphioxus being excluded, the following arrangement 

 results. The Pisces are the most primitive and from them arose 

 the Amphibia, from the Amphibia again, the Reptilia, and from 

 these, on one side, Aves, on the other, Mammalia. The story 

 from the earth's strata corresponds closely with this. Fish are the 

 only Vertebrates of the Silurian and Devonian. The earliest Amphibia 

 are found in the Carboniferous. In the great formation following, 



* From the nature of some of these old strata it can with certainty be asserted 

 that organisms must have assisted in their formation ; this is especially indicated by 

 the presence of chalk, graphite, and anthracite. 



