THE VICTORIAN NATURALIST. 135 



BARRIERS TO MIGRATION, AND THEIR EFFECTS AS 

 SHOWN IN THE AUSTRALIAN REGION. 



By Miss L. J. Little, B.Sc. 



(Read before the Field Naturalists' Club of Victoria, nth 

 September, 1893.^ 



My paper to-night is merely a compilation of the work of the 

 latest authorities, often given in their own words. It is in no 

 sense original work. I am chiefly indebted to my teachers, to 

 A. R. Wallace, and to Professor Tate. 



Bibliography : — Dr. Dendy's " Lectures on Geographical Dis- 

 tribution ; " Professor Heilprin's " Distribution of Animals ;" Sir J. 

 Hooker's " Flora of New Zealand ; " Captain Hutton's "Origin of 

 Flora and Fauna of New Zealand " (" Annals and Magazine of 

 Natural History, 1884-85);" R. Lydekker, Nature, 5th May, 

 1892; Sir F. M'Coy's " Prodromus of Victoria;" Professor 

 Spencer's " Fauna and Zoological Relationships of Tasmania " 

 (Australasian Association for the Advancement of Science) — 

 Lectures on Zoology ; Professor Tate's " On the Influence of 

 Physiographic Changes " (Australasian Association) ; A. R. 

 Wallace's "Island Life," 2nd edition; "Darwinism," 3rd edition. 



Every foot of dry land has at one time or another formed part 

 of a sea bottom. As the earth rises and falls each continent 

 sinks beneath the sea again and again, and yet it never ceases to 

 exist as a continent. 



Connections between distant lands are made only to be broken, 

 and as one geological age succeeds another the shape and condition 

 of every land are altered. Yet the researches of the Challenger 

 show that all land debris brought down by rivers to the ocean is 

 deposited comparatively near the shore. Sand and gravel is laid 

 down within a very few miles of shore ; only fine sediment to 50 

 miles, and the very finest to 150 miles. New, the whole series of 

 marine stratified rocks, from the earliest Palgeozoic to the recent 

 Tertiary beds, consist of materials corresponding to those now 

 being deposited within this narrow belt. Therefore all these 

 stratifications must have been laid in shallow water and near to 

 existing continental lands. There Nature has always strewn the 

 dust of continents to be ; and, according to Wallace, if we trace 

 the 1,000 fathom line round all our existing continents, we mark 

 out approximately the continental area— that is, the limits within 

 which changes of land and sea have gone on during geological 

 time. Inside this line has always been land and shallow sea in 

 varying proportions. Yet we must remember that a depth of even a 

 few feet of water would prevent the existence of terrestrial 

 animals. It is impossible to exaggerate, or even to conceive, the 

 effect of the endless mutations on the animal world. The whole 

 population of living things slowly but surely must have been 



