442 Life and Inamortality. 
world has been geologically explored; that only organic 
beings of certain classes, at least in any great number, can be 
preserved in a fossil condition; that many species when 
once formed never undergo any further change, but become 
extinct without leaving any modified descendants ; that domi- 
nant and widely-ranging species vary the most and the most 
frequently, and that varieties are often at first only local, it 
is not at all surprising that the discovery of intermediate 
links to any considerable extent should not have been made. 
Local varieties, as is well known, will not diffuse themselves 
into other and distant localities until they have become 
very much modified and improved, and when they have thus 
diffused themselves, and are discovered in a geological forma- 
tion, they will appear as if suddenly created there, and will 
simply be ranked as new species. Besides, formations have 
often been intermittent in their accumulation, and their dura- 
tion has probably been shorter than the average duration of 
specific forms. And as successive formations in most cases 
are separated from each other by blank intervals of time of 
considerable length, and as fossiliferous formations thick 
enough to withstand future degradation can as a general 
rule be accumulated only where much sediment is laid down 
in the subsiding bed of the ocean, it follows that during the 
alternate periods of elevation and of stationary level the 
record will generally be blank or devoid of fossil remains. 
During these latter periods there will doubtless be more 
variability in the forms of life, and during the periods of 
subsidence a greater amount of extinction. Now, as geology 
plainly declares that each land has undergone great physical 
changes, we have a right to expect that organic beings have 
varied under nature in the same manner as they have varied 
under domestication, and such have scientific study and 
research found to be the case. And if there has been any 
variability under nature, such a fact would seem unaccount- 
able unless Natural Selection, or the Survival of the Fittest, 
did not come into play. Upon the view that variations have 
