Paleontology. 159 



leaving an impression ; that this surface should 

 afterwards have hardened sufficiently to retain the 

 impression ; that it should then have been protected 

 from the erosion of water, as well as from the dis- 

 integrating influence of the air ; and yet that it should 

 not have sunk far enough beneath the surface to have 

 come within the no less disintegrating influence of 

 subterranean heat Remembering thus, as a general 

 rule, how many conditions require to have met before 

 a fossil can have been both formed and preserved, 

 we must conclude that the geological record is pro- 

 bably as imperfect in itself as are our opportunities of 

 reading even the little that has been recorded. If we 

 speak of it as a history of the succession of life upon 

 the planet, we must allow, on the one hand, that it is 

 a history which merits the name of a " chapter of 

 accidents"; and, on the other hand, that during the 

 whole course of its compilation pages were being 

 destroyed as fast as others were being formed, while 

 even of those that remain it is only a word, a line, or 

 at most a short paragraph hen and there, that we are 

 permitted to see. With so fragmentary a record as 

 this to study, I do not think it is too much to say 

 that no conclusions can be fairly based upon it, 

 merely from the absence of testimony. Only if the 

 testimony were positively opposed to the theory of 

 descent, could any argument be fairly raised against 

 that theory on the grounds of this testimony. In 

 other words, if any of the fossils hitherto discovered 

 prove the order of succession to have been incom- 

 patible with the theory of genetic descent, then the 

 record may fairly be adduced in argument, because 

 we should then be in possession of definite information 



