PRINCIPLES OF GEOLOGY. 13 



of existence. They may thus be successively compared with the analo- 

 gous beings now living, and with one another. This comparison elicits 

 most curious and interesting results. 



First, we perceive that nearly all the immense multitude of buried 

 beings belongs to species different from any that now exist ! but in this 

 difference between fossil and recent specimens, are several degrees ; some 

 species are allied, others are analogous, and the remainder so discrepant, 

 as to bear hardly any mutual resemblance. 



Now, it is an established fact, that the greater number of fossils 

 which nearly resemble living objects, belongs to the most recent of all 

 the strata, viz. those above the chalk ; and that many of the extinct 

 genera are confined to the lowest and oldest part of the series. Place 

 together, for instance, existing species of shells, and the fossils of the least 

 ancient of British strata, as those of Hordwell and the Isle of Wight, 

 the resemblance is obvious and decided ; but on a similar comparison be- 

 tween recent specimens and the fossil productions of the mountain lime- 

 stone, one of the oldest of the secondary rocks, the difference is evident 

 and remarkable. Considered in this manner, the living and fossil tribes 

 constitute one mighty series of organic productions, formed upon one 

 general plan, but called successively into existence, to suit the changing 

 conditions of the earth and the ocean. The striking contrast between 

 the imbedded fossils of different rocks, has given rise to an opinion, 

 that, whilst the strata were successively deposited, many races of organic 

 bodies became extinct, and others were created to supply their place, 

 more and still more nearly assimilated to the present productions of 

 nature. 



WE must now attend to certain phenomena, in the relative positions 

 of rocks, which demonstrate that the internal parts of our planet have 

 been shaken by often-repeated convulsions. Rocks appear generally in 

 planes, deviating but little from the horizontal, but sometimes they de- 



