SUCCESSION OF LIFE UPON THE GLOBE. 367 
CHAPTER 22XHE 
THE SUCCESSION OF LIFE*UPON THE GLOBE. 
In conclusion, it may not be out of place if we attempt to 
summarise, 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 Palseontology. 
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 
place, quite certain that there has been a similar saccession in 
the order of appearance of the primary groups (‘ sub-king- 
doms,” “classes,” &c.) of animals and vegetables. These 
great groups did not all come into existence at once, but they 
made their appearance successively. It is true that we can- 
not be said to be certainly acquainted with the first absolute 
