GEOGRAPHICAL REVOLUTIONS. 347 



whatever elevations and subsidences these countries may 

 have undergone, they have not been connected either with 

 Asia, Africa, or South America during the whole 

 Tertiary period. 



In conclusion, I would especially remark that the 

 various changes in the outlines and mutual relations 

 of our continents, which I have now endeavoured to 

 establish, must not be supposed to have been all strictly 

 contemporaneous. Some may have been a little earlier 

 or a little later than others ; some changes may have 

 been slower, others more rapid ; some may have had but 

 a short duration, while others may have persisted through 

 considerable geological periods. But, notwithstanding 

 this uncertainty as to details, the great features of the 

 geographical revolutions which I have indicated, appear 

 to be established by a mass of concurring evidence ; and 

 the lesson they teach us is, that although almost the 

 whole of what is now dry land has undoubtedly once 

 lain deep beneath the waters of the ocean, yet such 

 changes on a great scale are excessively slow and gradual ; 

 so that, when compared with the highest estimates of 

 the antiquity of the human race, or even with that of 

 most of the higher animals, our existing continents and 

 oceans may be looked upon as permanent features of 

 the earth's surface. 



