Page:A sketch of the physical structure of Australia.djvu/104

92 detected under the strict generic resemblance of the fauna and flora of different parts of Australia.

The mountain chains of old rocks have not only passed through the destructive plains of the sea level; and been everywhere subject to the wearing action of its breakers, which, in addition to the dislocating and disturbing forces acting on the interior, must have destroyed and removed so large a portion of their mass; but they must for long, long ages have stood the wear and tear of the wind and the rain, and the other atmospheric causes of degradation and disintegration which would sufficiently account for their remarkably furrowed character, their deep erosion into valleys and ravines, which even where the rocks are but little disturbed, is so striking a characteristic of many of the old rocks of this country. On the contrary, the tertiary rocks having been merely elevated en masse, and that, geologically speaking, at so recent a date, form level or gently undulating and unbroken plains, which are an equal characteristic of the Australian land.

I believe, partly from my own observation, partly from the oral information or the published accounts of others, that the plants and animals of Australia, though everywhere similar, or to speak strictly, though every where of the same order and family, and commonly of the same genus, yet vary in species and sometimes in genus, not simply with