Page:Australia, from Port Macquarie to Moreton Bay.djvu/28

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7
GEOLOGICAL FORMATION.

marked influence on the comparative fertility of the soil of their respective alluvial lands. For instance, in examining a well dried handful of alluvial soil, taken from the banks of the MacLeay river, with a microscope, I saw in it minute particles of felspar, and quartz, and little thin laminae of mica; thus at once indicating, that in the basin of this river there is a preponderance of primitive rooks. Now soil containing minute particles of these kinds of rocks, would, of course, have different qualities from soil in which particles of other kinds of rock, such as sandstone, predominated.

Professor Jameson has made the following apposite remarks on the different qualities of alluvial soils produced from this cause.—"The varieties of transported soil depend chiefly upon three circumstances: first, the nature of the rocks from which they are derived; 2ndly, the quality and effect of the moving powers; 3rdly, the changes which they may have undergone after their formation. The origin of the materials, which enter into the composition of transported soil, has already been considered. From their difference may be easily explained why soil generated from the debris of primitive crystalline rocks, has different qualities from soil which has been derived from strata of sandstone."

There is, indeed, scarcely any country where the surface rocks exercise so great an influence on the fertility of the soil, and the aspect of the vegetation, as in Australia. Thus, sandstone, the all-pervading