XX CONTENTS. 



CHAPTEB X. 



ON THE IMPERFECTION OP THE GEOLOGICAL EECOBD. 



Page. 

 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 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 knovpn fossiliferous strata — Antiquity of 

 the habitable earth 312 



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 343 



CHAPTER XII. 



GEOGRAPHICAL DISTHIBtTTION. 



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 P»a 



CHAPTEB XIII. 



GEOGRAPHICAL DISTRIBUTION— COreimMed. 



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 



