274 MAN'S PLACE IN THE GEOLOGICAL EECORD. 



rences of the existing epoch. We can judge from its thick- 

 ness, and the nature of its rocks and fossils, that one sys- 

 tem took much longer time to accumulate than another, 

 "but we cannot venture, by any known method of compu- 

 tation, to say how long in years. All that we have to do 

 with is relative time ; and even in dealing with the current 

 epoch, should we assert that certain events took place more 

 than six thousand or eight thousand years ago, we are 

 simply asserting a provisional opinion, and not maintain- 

 ing a belief like that founded upon the written record of 

 human history. 



The geological record is thus relative and not absolute ; 

 and when we arrange it, as in the subjoined tabulation, 

 into Primary, Secondary, Tertiary, and Quaternary, we are 

 merely asserting a certain order of succession, and this suc- 

 cession not always clearly defined over certain areas. In- 

 deed, it is often impossible to define the boundaries of the 

 minor stages, portions having been removed by denudation, 

 others overlaid by more recent deposits, and some being 

 partially submerged beneath the waters of the ocean. Again, 

 though the thickness of one formation may seem to have 

 required a longer time for its accumulation than another of 

 smaller dimensions, yet in the one case the rate of deposi- 

 tion may have been much more rapid than in the other, 

 and the thinner may, after all, have required the longer 

 period. Still further, though organic remains are most im- 

 portant aids, yet they are often absent from certain beds, or 

 if there, these beds are not sufficiently exposed to investi- 

 gation, and our information becomes in this way fragmen- 

 tary and defective. Neither in sequence of events, nor in 

 expression of time, does Geology lay claim to exactitude. 

 Its cultivators are successfully labouring to complete the 

 one, and they are hopeful of arriving at more definite terms 

 in the other ; but this is all in the mean time, and the fol- 



