XX CONTENTS. 



CHAPTER X. 



OTT THE IirPERFECTION OF THE GEOLOGICAL HECOHD. 



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 rale of 

 denudation and of deposition — On the lapse of time as esti- 

 mated by years — On the poorness of our palseontological col- 

 lections — On the intermittence of geological formations — On 

 the denudation of granitic areas — On the absence of inter- 

 mediate varieties in any one formation — On the sudden 

 appearance of groups of species — On their sudden appear- 

 ance in the lowest known fossiliferous strata — Antiquity of 

 the habitable earth 313 



CHAPTER XI. 



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 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 843 



CHAPTER XII. 



GEOGRAPHICAL DISTRIBUTIOK. 



Present distribution cannot be accounted for by differences 

 in physical conditions — Importance of barriers — Affinity 

 of the productions of the same continent — Centers of crea- 

 tion — 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 „ 375 



CHAPTER 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 



