flil CONTENTS. 



CHAPTER X. 

 ON THK 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 f time as estimated by years On the poorness of our palaeonto- 

 logical 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 247 



CHAPTER XL 

 O.v 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 . . . . . . . . . . 272 







CHAPTER XIL 



GEOGRAPHICAL DISTRIBUTION. 



Present distribution cannot be accounted for by differences in physical con- 

 ditions 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 



296 



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 those of the nearest mainland On colonisation 

 from the nearest source with subsequent modification Summary of the 

 last and present chapter . . . . . . . . . . . . 322 



