SIR CHARLES LYELL 211 



coasts, the growth of new deltas, the increase of coral reefs, volcanic 

 eruptions, and other changes. 



Uniformity of change considered, secondly, in reference to the liv- 

 ing creation. — Secondly, ifi regard to the vicissitudes of the living 

 creation, all are agreed that the successive groups of sedimentary strata 

 found in the earth's new crust are not only dissimilar in mineral com- 

 position 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, arranged 

 in chronological order, is this : that at successive 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 inquire whether it has 

 now become fixed and stationary, we discover 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 success- 

 fully 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 conspicuous. It will nevertheless appear evident, from the 

 facts and arguments detailed in the chapters which treat of the geo- 

 graphical distribution of species in the next volume, that man is not 

 the only exterminating agent ; and that, independently of his inter- 

 vention, 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 geography and climate of the 

 globe cannot fail to have the same tendency. If we proceed still 

 farther, and inquire whether new species are substituted from time to 

 time for those which die out, we find that the successive introduction 

 of new forms appears to have been a constant part of the economy of 

 the terrestrial system, and if we have no direct proof of the fact it is 

 because the changes take place so slowly as not to come within the 

 period of exact scientific observation. To enable the reader to appre- 



