SUCCESSION OF LIFE UPON THE GLOBE. 381 



CHAPTER XXIII. 



THE SUCCESSION OF LIFE UPON THE GLOBE. 



In conclusion, it may not be out of place if we attempt to 

 summarize, in the briefest possible manner, some of the prin- 

 cipal results which may be deduced as to the succession of 

 life upon the earth from the facts which have in the preceding 

 portion of this work been passed in review. That there was 

 a time when the earth was void of life is universally admitted, 

 though it may be that the geological record gives us no direct 

 evidence of this. That the globe of to-day is peopled with 

 innumerable forms of life whose term of existence has been, 

 for the most part, but as it were of yesterday, is likewise an 

 assertion beyond dispute. Can we in any way connect the 

 present with the remote past, and can we indicate even im- 

 perfectly the conditions and laws under which the existing 

 order was brought about? The long series of fossiliferous 

 deposits, with their almost countless organic remains, is the 

 link between what has been and what is; and if any answer 

 to the above question can be arrived at, it will be by the 

 careful and conscientious study of the facts of Palaeontology. 

 In the present state of our knowledge, it may be safely said 

 that anything like a dogmatic or positive opinion as to the 

 precise sequence of living forms upon the globe, and still 

 more as to the manner in which this sequence may have been 

 brought about, is incapable of scientific proof. There are, 

 however, certain general deductions from the known facts 

 which may be regarded as certainly established. 



In the first place, it is certain that there has been a succession 

 of life upon the earth, different specific and generic types suc- 

 ceeding one another in successive periods. It follows from 

 this, that the animals and plants with which we are familiar as 

 living, were not always upon the earth, but that they have been 

 preceded by numerous races more or less differing from them. 

 What is true of the species of animals and plants, is true also 

 of the higher zoological divisions; and it is, in the second 



