96 THE ORIGIN OF SPECiEB 



CHAPTER XI 



ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 



On the slow and successive appearance of new species — On their dififerent 

 rates of change — Species once lost do not reappear — Groups of species 

 follow the same general rules in their appearance and disappearance as 

 do single species — On Extinction — On simultaneous changes in the 

 forms of life throughout the world — On the affinities of extinct species 

 to each other and to living species — On the state of development of 

 ancient forms — On the succession of the same types within the same 

 areas — Summary of preceding and present chapter 



LET US now see whether the several facts and laws 

 relating to the geological succession of organic 

 beings accord best with the common view of 

 the immutability of species, or with that of their slow 

 and gradual modification, through variation and natural 

 selection. 



New species have appeared very slowly, one after 

 another, both on the land and in the waters. Lyell 

 has shown that it is hardly possible to resist the evi- 

 dence on this head in the case of the several tertiary 

 stages; and every year tends to fill up the blanks be- 

 tween the stages, and to make the proportion between 

 the lost and existing forms more gradual. In some of 

 the most recent beds, though undoubtedly of high an- 

 tiquity if measured by years, only one or two species 

 are extinct, and only one or two are new, having ap- 

 peared there for the first time, either locally, or, as far 



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