A ON THE LAW WHICH HAS REGULATED 



inhabiting it, is but the last stage of a long and 

 uninterrupted series of changes which it has under- 

 gone, and consequently, that to endeavour to explain 

 and account for its present condition without any 

 reference to those changes (as has frequently been 

 done) must lead to very imperfect and erroneous 

 conclusions. 



The facts proved by geology are briefly these : 

 That during an immense, but unknown period, the 

 surface of the earth has undergone successive 

 changes; land has sunk beneath the ocean, while 

 fresh land has risen up from it; mountain chains 

 have been elevated ; islands have been formed into 

 continents, and continents submerged till they have 

 become islands ; and these changes have taken place, 

 not once merely, but perhaps hundreds, perhaps 

 thousands of times : That all these operations have 

 been more or less continuous, but unequal in their 

 progress, and during the whole series the organic 

 life of the earth has undergone a corresponding 

 alteration. This alteration also has been gradual, 

 but complete ; after a certain interval not a single- 

 species existing which had lived at the commence- 

 ment of the period. This complete renewal of the 

 forms of life also appears to have occurred several 

 times : That from the last of the geological epochs 

 to the present or historical epoch, the change of 

 organic life has been gradual : the first appearance 

 of animals now existing can in many cases be traced, 

 their numbers gradually increasing in the more re- 



