Chap. XIV. 
EECAPITULATION. 
463 
links between them, but only between each and some 
extinct and supplanted form. Even on a wide area, 
which has during a long period remained continuous, 
and of which the climate and other conditions of life 
change insensibly in going from a district occupied by 
one species into another district occupied by a closely 
allied species, we have no just right to expect often to 
find intermediate varieties in the intermediate zone. 
For we have reason to believe that only a few species 
are undergoing change at any one period; and all 
changes are slowly effected. I have also shown that the 
intermediate varieties which will at first probably exist 
in the intermediate zones, will be liable to be sup¬ 
planted by the allied forms on either hand; and tlie 
latter, from existing in greater numbers, will generally 
be modified and improved at a quicker rate than the 
intermediate varieties, which exist in lesser numbers; 
so that the intermediate varieties will, in the long run, 
be supplanted and exterminated. 
On this doctrine of the extermination of an infinitude 
of connecting links, between the living and extinct in- 
habitauts of the world, and at each successive period 
between the extinct and still older species, why is not 
every geological formation charged with such links? 
Why does not every collection of fossil remains afford 
plain evidence of the gradation and mutation of the 
forms of life? We meet with no such evidence, and this 
is the most obvious and forcible of the many objections 
which may be urged against my theory. Why, again, 
do whole groups of allied species appear, though cer¬ 
tainly they often falsely appear, to have come in sud¬ 
denly on the several geological stages ? Why do we not 
find great piles of strata beneath the Silurian system, 
stored with the remains of the progenitors of the Silurian 
groups of fossils? For certainly on my theory such 
