President's Address. 



315 



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- 

 lowing arrangement expresses the amount of their informa- 

 tion : — 



Cainozoic j Quaternary or Recent formations. 



(Recent Life). \ Tertiary. 



C Cretaceous or Chalk. 

 < Oolitic or Jurassic. 



Mesozoic 



(Middle Life). y Triassic or Upper New Red Sandstone. 



I Permian or Lower New Red Sandstone. 

 Carboniferous or Coal System. 

 Old Red Sandstone and Devonian. 

 Silurian. 

 Eozoic f Cambrian. 



{Dawn Life). \ Laurentian. 



In this arrangement the terms Eozoic, Palaeozoic, Mesozoic, 

 and Cainozoic, indicate the chronological stages having re- 

 ference to the ascent of life ; and Laurentian, Cambrian, 

 Silurian, &c, those having reference to the different forma- 

 tions whose depositions mark the successive physical opera- 

 tions of nature. By this arrangement the geologist simply 

 asserts that the Laurentian preceded the Cambrian, and the 

 Cambrian the Silurian, but no opinion is expressed as to 

 the amount of time required for the deposition of the Lau- 



