Uniformity in Geological Change 



tion for reasons above alluded to, but are likewise 

 distinguishable from each other by their organic 

 remains. The general inference drawn from the 

 study and comparison of the various groups, ar- 

 ranged in chronological order, is this: that at suc- 

 cessive periods distinct tribes of animals and plants 

 have inhabited the land and waters, and that the 

 organic types of the newer formations are more 

 analogous to species now existing than those of 

 more ancient rocks. If we then turn to the present 

 state of the animate creation, and enquire whether 

 it has now become fixed and stationary, we dis- 

 cover that, on the contrary, it is in a state of 

 continual flux that there are many causes in 

 action which tend to the extinction of species, 

 and which are conclusive against the doctrine 

 of their unlimited durability. 



There are also causes which give rise to new 

 varieties and races in plants and animals, and 

 new forms are continually supplanting others 

 which had endured for ages. But natural history 

 has been successfully cultivated for so short a 

 period, that a few examples only of local, and 

 perhaps but one or two of absolute, extirpation 

 of species can as yet be proved, and these only 

 where the interference of man has been conspicu- 

 ous. It is evident that man is not the only ex- 

 terminating agent; and that, independently of 

 his intervention, the annihilation of species is 

 promoted by the multiplication and gradual 

 diffusion of every animal or plant. It will also 

 appear that every alteration in the physical 

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