CONTENTS OF VOL. IL 



CHAPTER IX, 



BTBKIDISH. 



Distinction between the sterility of first crosses and of hybrids — 

 Sterility various in degree, not universal, aSected by close in- 

 terbreeding, removed by domestication — Laws governing the 

 sterility of hybrids — Sterility not a special endowment, but 

 incidental on other differences, not accumulated by natural 

 selection — Causes of the sterility of first crosses and of hybrids 

 — Parallelism between the effects of changed conditions of life 

 and of crossing — Dimorphism and trimorphism — Fertility of 

 varieties when crossed and of their mongrel offspring not uni- 

 versal — Hybrids and mongrels compared independently of their 

 fertility — Summary Page 1 



CHAPTER X. 



ON THE IMPERFECTION OF THE OEOLOeiCAL KEeoSD. 



On the absence of intermediate varieties at the present day — On 

 the nature of extinct intermediate varieties ; on their number — 

 On the lapse of time, as inferred from the rate of denudation - 

 and of deposition — On the lapse of time as estimated by years 

 — On the poorness of our pal»ontological collections — On the 

 intermittence of geological formations — On the denudation of 

 granitic areas — On the absence of intermediate varieties in any 

 one formation — On the sudden appearance of groups of species 

 — On their sudden appearance in the lowest known fossiltferous 

 strata — Antiquity of the habitable earth .... 48 



