ORIGIN OF THE ANIMATED TRIBES. 



79 



rocks, which is precisely what might be expected, since 

 lime is necessary for the formation of the shells of the 

 mollusks and articulata, and the hard substance of the 

 crinoidea and corals; next in the carboniferous series; 

 next in the tertiary ; next in the new red sandstone ; next 

 in slates ; and lastly, least of all, in the primary rocks.* 

 This may have been the case without regard to the origi- 

 nation of new species, but more probably it was other- 

 wise ; or why, for instance, should the polypiferous zoo- 

 phyta be found almost exclusively in the limestones? 

 There are, indeed, abundant appearances as if, through- 

 out all the changes of the surface, the various kinds of 

 organic life invariably pressed in, immediately on the 

 specially suitable conditions arising, so that no place 

 which could support any form of organic being, might be 

 left for any length of time unoccupied. Nor is it less re- 

 markable how various species are withdrawn from the 

 earth, when the proper conditions for their particular 

 existence are changed. The trilobite, of which fifty spe- 

 cies existed during the earlier formations, was extirpated 

 before the secondary had commenced, and appeared no 

 more. The ammonite does not appear above the chalk. 

 The species, and even genera of all the early radiata and 

 mollusks were exchanged for others long ago. Not one 

 species of any creature which flourished before the ter- 

 tiary (Ehrenberg's infusoria excepted) now exists; and 

 of the mammalia which arose during that series, many 

 forms are altogether gone, while of others we have now 

 only kindred species. Thus to find not only frequent 

 additions to the previously existing forms, but frequent 

 withdrawals of forms which had apparently become inap- 

 propriate — a constant shifting as well as advance — is a 

 fact calculated very forcibly to arrest attention. 



A candid consideration of all these circumstances can 

 scarcely fail to introduce into our minds a somewhat dif- 

 ferent idei of organic creation from what has hitherto 

 been genr rally entertained. That God created animated 

 beings a? well as the terraqueous theatre of their being, 

 is a fact i > powerfully evidenced, and so universally re- 

 ceived, tl at I at once take it for granted. But in the par- 

 ticulars of this so highly supported idea, we surely here 

 see cause for some re-consideration. It may now T be in- 



* See paper by Professor Edward Forbes, read to the British 

 Association, 1839. 



