rom the rate of denudation and of deposition--On
the lapse of time as estimated in years--On the poorness of our
palaeontological 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.

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.

CHAPTER XII.

GEOGRAPHICAL DISTRIBUTION.

Present 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.

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.

CHAPTER XIV.

MUTUAL AFFINITIES OF ORGANIC BEINGS: MORPHOLOGY--EMBRYOLOGY--RUDIMENTARY
ORGANS.

Classification, groups subordinate to groups--Natural system--Rules and
difficulties in classification, explained on the theory of descent
with modification--Classification of varieties--Descent always used in
classification--Analogical or adaptive characters--Affinities,
general, complex and radiating--Extinction separates and defines
groups--Morphology, between members of the same class, between parts of
the same individual--Embryol