172 STUDIES IN LIFE AND SENSE. 



and grew apace, comparatively unmolested by carnivora or other 

 enemies. Again extending their range northwards, they are found 

 in North America ; and they thus represent in the Western Hemi- 

 sphere a flourishing remnant of a race killed off from the Old World, 

 and driven, by stress of outward circumstances, to seek refuge in 

 the New. 



Not less interesting is it to find that the existing life of Australia 

 at large fully endorses the biological dictum that in this island terri- 

 tory we find still represented the life which was once world-wide in 

 its extent in the Triassic and Oolitic period, in which period Australia 

 severed its connection with the Asiatic continent. As the marsupial 

 quadrupeds of the Oolite overran the existing land area of that day, 

 so they flourish, and flourish alone, in the Australia we ourselves know. 

 As the spine-bearing Port Jackson shark swims in the Australian 

 seas to-day, so the spiny fishes Acrodus and Strophodus swam in 

 the Oolitic seas that washed Palsearctic and other coasts. As the 

 shell-fish Trigonia lived in the seas of the Stonesfield Slate period 

 around our shores, so that Trigonia still persists on the Australian 

 coasts alone. And, lastly, as the Araucarian pines and cycads 

 grew in Oolitic times in our own area, so they grow now in Australian 

 territory a remnant, like the quadrupeds and fishes, of a flora and 

 fauna once well-nigh universal, but now limited to the region of the 

 earth wherein alone the original conditions of their life are truly 

 represented. 



If geological change isolating or uniting land areas, and the 

 variation and modification of species consequent upon such separa- 

 tion or union, be thus credited with constituting the great factors 

 and powers which have produced the existing distribution of animals 

 and plants, and which have regulated that distribution in all time 

 past, we may now briefly glance at the main features which the 

 great biological regions of the world have exhibited in relation to the 

 changes and alterations of their boundaries they have from time to 

 time undergone. 



Whilst the late Sir Charles Lyell and other geologists were found 

 not so long ago to declare that the great continents of the world 

 " shift their positions entirely in the course of ages," a clearer under- 

 standing of geological evidence has completely established the doc- 

 trine of the permanence of the great continental areas, and of the 

 general stability in time of the main masses of the land. It is need- 

 ful to make ourselves acquainted with this fact, inasmuch as, if the 

 distribution of life depends primarily on the distribution of land and 

 sea, a clear understanding of the agencies regulating the develop- 

 ment of animals and plants on the globe will be gained only when 

 the physical changes in question are duly appreciated. The geolo- 

 gical evidence, then, goes to prove that, whilst the general mass of the 



