Chap. XIV. RECAPITULATION. 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 the 

 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- 

 habitants 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 tins 

 is the most obvious and forcible of the many objections 

 winch 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 



