Vlil 
CONTENTS. 
CHAPTEE IX. 
On the Impekfection of the Geological Eecord. 
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 palaeontological 
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 Okganic 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, 
I and by occasional means — Dispersal during the Glacial period 
i , co-extensive with the world. 346-382 
