464 



ISLAND LIFE. 



[part ir. 



tliat are represented there by a very few species only, and these 

 180 genera include nearly 1,100 species." 



Geological explanatio7i of the differences of these tiuo Floras, — 

 These facts again clearly point to the conclusion, that South- 

 western Australia is the remnant of the more extensive and 

 more isolated portion of the continent in which the peculiar 

 Australian flora was principally developed. The existence there 

 of a very large area of granite — 800 miles in length by nearly 

 500 in maximum width, indicates such an extension; for this 

 granitic mass was certainly once buried under piles of stratified 

 rock, since denuded, and then formed the nucleus of the old 

 Western Australian continent. If we take the 1000-fathom 

 line around the southern part of Australia to represent the 

 probable extension of this old land we shall see that it would 

 give a wide additional area south of the Great Australian 

 Bight, and form a continent which, even if the greater part of 

 tropical Australia were submerged, would be sufficient for the 

 development of a peculiar and abundant flora. We must also 

 remember that an elevation of 6000 feet, added to the vast 

 amount which has been taken away by denudation, would 

 change the whole country, including what are now the deserts 

 of the interior, into a mountainous and well-watered region. 



But while this rich and peculiar flora was in process of forma- 

 tion, the eastern portion of the continent must either have been 

 widely separated from the western or had perhaps not yet risen 

 from the ocean. The whole of this part of the country consists 

 of Palgeozoic and Secondary formations with granite and meta- 

 morpliic rocks, the Secondary deposits being largely developed 

 on both sides of the central range, extending the whole length 

 of the continent from Tasmania to Cape York, and constituting 

 the greater part of the plateau of the Blue Mountains and other 

 lofty ranges. During some portion of the Secondary period, 

 therefore, this side of Australia must have been almost wholly 

 submerged beneath the ocean ; and if we suppose that during 

 this time the western part of the continent was at nearly its 

 maximum extent and elevation, we shall have a sufficient ex- 

 planation of the great difference between the flora of Western 

 and Eastern Australia, since the latter would only have been 



