Vlll CONTENTS. 



CHAPTEE IX. 



On the Imperfection of the Geological Record. 



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

 the nature of extinct intermediate varieties ; on their number — 

 On the vast lapse of time, as inferred from the rate of deposi- 

 tion and of denudation — On the poorness of our paheontological 

 collections — On the intermittence of geological formations — 

 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 fossiliferous strata 



Page 279-311 



CHAPTEE X. 



On the Geological Succession of Organic Beings. / 



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

 different rates of change — Species once lost do not reappear — 

 Groups of species follow the same general rules in their appear- 

 ance 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 chapters . . . . 312-345 



CHAPTEE XL 



Geographical Distribution. 



Present distribution cannot be accounted for by differences in phy- 

 sical conditions — Importance of barriers' — Affinity of the pro- 

 ductions of the same continent — Centres of creation — Means 

 of dispersal, by changes of climate and of the level of the land, 

 and by occasional means — Dispersal during the Glacial period 

 co-extensive with the world 346-382 



