140 GRADUAL MODIFICATION OF ANIMAL FORMS xi 



Why should they not yield to us the knowledge we are all 

 so eager to acquire ? 



If species are and ever have been immutable, shall we not 

 find the same hard and fast lines surrounding each as we do 

 now ? Shall we not find long series of similar forms following 

 without change on an abrupt commencement? If the other 

 alternative be correct, ought we not to find specimens of all 

 the various stages through which the wonderful variety we 

 meet with now has been brought about ? Every gap which 

 now so widely separates group from group ought to be filled 

 up, and the various phases of modification should follow 

 through the successive eras of geological time. 



Now, there can be no hesitation in saying that the evidence 

 of palaeontology, in the present state of the science, does not 

 reveal the last-described condition of things. Notwithstanding 

 the vast increase of our knowledge in recent years, very many 

 large groups of animals stand completely isolated, and the 

 more nearly allied forms are mostly separated from each other 

 by tolerably definite intervals. 



Is, then, the question decisively answered against evolution 

 or derivation by palaeontology ? 



"We must pause before we can join in the assertion that it 

 is. The subject is far more complex than it may seem at 

 first. 



Before going further, a proper estimate must be arrived at 

 of the nature and value of our evidence, and in doing this we 

 must give full weight to the considerations derived from the 

 " imperfection of the geological record " so strikingly elucidated 

 in Mr. Darwin's chapter on the subject. 



To those who have not fully considered this question, it is 

 difficult to conceive how immense is the interval between our 

 excessively fragmentary knowledge of extinct animals, and 

 that perfect palseontological record which would imply evidence, 

 first, of every form of life that has ever existed, and, secondly, 

 of the period at which it existed. 



If there were time, I might dwell long upon this part of 

 the subject, but I must leave you to imagine (1) What the 

 chances are against the fossilisation of any animal that dies. 

 (2) What the chances of the stratum in which some fossil 



