THEORY OP tHfc EARTH. 119 



This objection may appear strong to those who 

 believe in the indefinite possibility of change of 

 forms in organized bodies, and think that during a 

 succession of ages, and by alterations of habitudes, 

 all the species may change into each other, or one 

 of them give birth to all the rest. Yet to these 

 persons the following answer may be given from 

 their own system : If the species have changed by 

 degrees, as they assume, we ought to find traces of 

 this gradual modification. Thus, between the 

 palcEothcrium and the species of our own days, we 

 should be able to discover some intermediate 

 forms ; and yet no such discovery has ever been 

 made. Since the bowels of the earth have not pre- 

 served monuments of this strange genealogy, we 

 have a right to conclude, That the ancient and now 

 extinct species were as permanent in their forms 

 and characters as those which exist at present ; or 

 at least, That the catastrophe which destroyed 

 them did not leave sufficient time for the produc- 

 tion of the changes that are alleged to have taken 

 place. 



In order to reply to those naturalists who ac- 

 knowledge that the varieties of animals are re- 

 strained by nature within certain limits, it would 

 be necessary to examine how far these limits ex- 

 tend. This is a very curious* inquiry, and in it- 

 self exceedingly interesting under a variety of 

 relations, but has been hitherto very little attend- 

 ed to. It requires that we should define accu- 



