CONTENTS. 



CHAPTEE X. 



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 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 palaiontological 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 fossiliferous strata — Antiquity of the habitable 

 earth Page 264-28S 



CHAPTEE XI. 



On the Geological Succession of Organic Beings. 



Oil 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 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 develop- 

 ment of ancient forms : — ■ On the succession of the same types within 

 the same areas — Summary of preceding and present chapter 290-315 



CHAPTEE XII. 



Geographical Distribution. 



I'jvsent distribution cannot be accounted for by differences in physical 

 conditions — Importance of barriers — Affinity of the productions 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 — Alternate Glacial periods in 

 the north and south 31G-342 



CHAPTEE XIII. 



Geographical Distribution — continued. 



Distribution of fresh-water productions — On the inhabitants of oceanic 

 islands — Absence of Batrachians and of terrestrial Mammals — On 

 the relation of the inhabitants of islands to those of the nearest main- 

 land — On colonization from the nearest source with subsequent modi- 

 fijfltion — Summary of the last and present chapter .. .. 343-S62 



