i8 Darwin, and after Darwin. 



possible for any one to believe with our forefathers 

 that the earth's surface has always existed as it now 

 exists. For the science of geology has proved to 

 demonstration that seas and lands are perpetually 

 undergoing gradual changes of relative positions — 

 continents and oceans supplanting each other in the 

 course of ages, mountain-chains being slowly uplifted, 

 again as slowly denuded, and so forth. Moreover, 

 and as a closer analogy, within the limits of animate 

 nature we know it is the universal law that every 

 individual life undergoes a process of gradual develop- 

 ment ; and that breeds, races, or strains, may be 

 brought into existence by the intentional use of 

 natural processes — the results bearing an unmistake- 

 able resemblance to what we know as natural species. 

 Again, even in the case of natural species themselves, 

 there are two considerations which present enormous 

 force from an antecedent point of view. The first 

 is that organic forms are only then recognised as 

 species when intermediate forms are absent. If the 

 intermediate forms are actually living, or admit of 

 being found in the fossil state, naturalists forthwith 

 regard the whole series as varieties, and name all 

 the members of it as belonging to the same species. 

 Consequently it becomes obvious that naturalists, in 

 their work of naming species, may only have been 

 marking out the cases where intermediate or con- 

 necting forms have been lost to observation. For 

 example, here we have a diagram representing a very 

 unusually complete series of fossil shells, which 

 within the last few years has been unearthed from 

 the Tertiary lake basins of Slavonia. Before the 

 series was completed, some six or eight of the then 



