CHAPTER XXIY. 



SUMMARY AND CONCLUSlOJf. 



The present volume is the develoiJiuent and application of a theory — State- 

 ment of the Biological and Physical causes of dispersal— Investigation 

 of the facts of dispersal — of tlie 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 Kemarks. 



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 main-y of tv;o 



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