CHAPTER XXIV. 
SUMMARY AND CONCLUSION. 
The present volume is the development and application of a theory — State- 
ment of the Biological and Physical causes of dispersal — Investigation 
of the facts of dispersal — of the means of dispersal — of geographical 
changes affecting dispersal — of climatal changes affecting dispersal — 
The glacial epoch and its causes — Alleged ancient glacial epochs — 
Warm polar climates and their causes — Conclusions as to geological 
climates — How far different from those of Mr. Croll — Supposed limita- 
tions of geological time — Time amply sufficient both for geological and 
biological development — Insular faunas and floras — The North Atlantic 
Islands — The Galapagos — St. Helena and the Sandwich Islands — Great 
Britain as a recent Continental Island — Borneo and Java — Japan and 
Formosa — Madagascar as an ancient Continental Island — Celebes and 
New Zealand as anomalous Islands — The Flora of New Zealand and 
its origin — The European element in the South Temperate Floras — 
Concluding Remarks. 
The present volume has gone over a very wide field both of 
facts and theories, and it will be well to recall these to the 
reader’s attention and point out their connection with each other, 
in a concluding chapter. I hope to be able to show that, 
although at first sight somewhat fragmentary and disconnected, 
this work is really the development of a clear and definite 
theory, and its application to the solution of a number of 
biological problems. That theory is, briefly, that the distri- 
bution of the various species and groups of living things over 
the earth’s surface, and their aggregation in definite assem- 
blages in certain areas, is the direct result and outcome of a 
complex set of causes, which may be grouped as “ biological ” 
and “physical.” The biological causes are mainly of two 
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