Page:Australia, from Port Macquarie to Moreton Bay.djvu/29

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rock of the central part of the colony, and of which the Blue Mountains are composed, from the Shoalhaven to the Liverpool range, except in a few places where it is overlaid by whinstone, is always indicative of barrenness and sterility; whilst nearly all the varieties of trap, with the clay slates, (so frequently met between the Hunter and Moreton), limestone and granite, are generally accompanied by good soil, and a more luxuriant vegetation. Thus the richness and tropical aspect of the isolated district of Illawarra, is principally attributable to the whinstone, of which the abrupt range, which separates it from the surrounding country, is composed; whilst a few of the higher summits near Sidney, such as Hay, Tomah, and Warrawolong, which consist of trap, are crowned with lofty trees, and stand conspicuously prominent amidst the miserable sandstone ridges around them. Sir Thomas Mitchell, in the valuable dissertation on the geology of the eastern part of New Holland, given in his interesting work, has observed, that, "by a little attention to the geological structure of Australia, we learn how much the superficial qualities of the soil and productions depend upon it, and where to look for arable spots amid the general barrenness." He also frequently alludes to the sterility of the country wherever sandstone occurs, whilst he observes, that trap forms an excellent soil on decomposition. Captain Sturt, also, was much struck with the apparent connection between the geology and vege-