CONTENTS. 
CHAPTER IV. 
evolution as the key to distribution. 
Importance of the Doctrine of Evolution — The Origin of New Species — Variation in 
Animals — The amount of variation in North American Birds — How new species 
arise from a variable species — Definition and Origin of Genera — Cause of the 
extinction of Species — The rise and decay of Species and Genera — Discontinuous 
specific areas, why rare — Discontinuity of the area of Parus palus'tris — Disconti- 
nuity of Emberiza schoeniclus — The European and J apanese J ays — Supposed ex- 
amples of discontinuity among North American Birds — Distribution and antiquity 
of Families — Discontinuity a proof of antiquity — Concluding Remarks 
Pages 54— 69 
CHAPTER Y. 
THE POWERS OF DISPERSAL OF ANIMALS AND PLANTS. 
Statement of the general question of Dispersal — The Ocean as a barrier to the dis- 
persal of Mammals — The dispersal of Birds — The dispersal of Reptiles — The 
dispersal of Insects — The dispersal of Land Mollusca — Great antiquity of Land- 
shells— Causes favouring the abundance of Land-shells — The dispersal of Plants 
— Special adaptability of Seeds for dispersal — Birds as agents in the dispersal of 
Seeds — Ocean currents as agents in Plant dispersal — Dispersal along mountain- 
chains — Antiquity of Plants as affecting their distribution . . Pages 70 — 80 
CHAPTER YI. 
GEOGRAPHICAL AND GEOLOGICAL CHANGES: THE PERMANENCE OF CONTINENTS. 
Changes of Land and Sea, their nature and extent — Shore-deposits and stratified 
rocks — The Movements of Continents — Supposed oceanic formations ; the Origin 
of Chalk— Fresh-water and Shore-deposits as proving the permanence of Conti- 
nents — Oceanic Islands as indications of the permanence of Continents and 
Oceans — General stability of Continents with constant change of form — Effect of 
Continental Changes on the Distribution of Animals — Changed distribution proved 
by the extinct animals of different epochs — Summary of evidence for the general 
permanence of Continents and Oceans ... . . Pages 81 — 102 
CHAPTER VII. 
CHANGES OF CLIMATE WHICH HAVE INFLUENCED THE DISPERSAL OF ORGANISMS ; 
THE GLACIAL EPOCH. 
Proofs of the recent occurrence of a Glacial Epoch — Moraines — Travelled Blocks — 
Glacial deposits of Scotland : the “ Till ” — Inferences from the glacial phenomena 
of Scotland — Glacial phenomena of North America — Effects of the Glacial Epoch 
on animal life — Warm and cold periods — Palaeontological evidence of alternate 
cold and warm periods — Evidence of interglacial warm periods on the Continent 
and in North America — Migrations and extinctions of Organisms caused by the 
Glacial Epoch Pages 103—120 
