18 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 
