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valleys is not less than half the length of the spurs which enclose them.
The country to the westward of the dividing range, considered, for the better illustration of the subject, as within limits corresponding to those of the country lying to the eastward,—that is to say, considered only at a distance of seventy-two miles from the crest of the dividing chain,—was found to have an average fall of twenty feet in every mile, and the average fall of its rivers to be nine feet in the same distance.
The crest of the dividing range, and of the spurs shooting from it, which form as it were the uppermost structure of the country, was stated to be composed of crystalline and siliceous rocks, as granite, gneiss, sienite, quartz-rock, protegene, hyalomicte, and petro'silex porphyry, and of trappean rocks, as serpentine, greenstone, basalt, and trachyte.
The next structure, which geologically may be called a superstructure, but which, from its relative height, is lower than, and abuts upon the first, is composed, on both sides of the before-mentioned dividing range, of analogous, though not identical stratified rocks, as mica, siliceous and argillaceous slates, limestones, conglomerates, breccias, and sandstones.
On a lower level of these, are the alluvial deposits confined to valleys.
In Van Diemen's Land, the dividing range, winding its course, in the form of a Z, through the island, which it apportions into very nearly equal parts, has an average height of 3750 feet, and an average distance from the sea of forty miles; the average fall of the rivers may be estimated at ninety-three feet per mile, and the average fall of the country at 120 feet.
Its geological fabric is, with very slight variation, identical with that of New South Wales, not only in structure, but in the nature of the materials of which it is composed: the difference lies only in the kind of rocks which constitute the crust of the two colonies.
In New South Wales, granite, sandstone, and conglomerates preponderate; in Van Diemen's Land, porphyry, greenstone, basalt, and trachyte.
In the former, limestone is confined to few localities; in the latter, that species of rock is more diffused.
From this difference in the geological materials of the two colonies, it necessarily follows that their respective soils must be different also.
This conclusion is borne out by the results of actual observation.
The analysis of the preponderating soils of the one and the other colony, shows, at the outset, that the soils of New South Wales contain from a quarter to one third less of matter soluble in hydrochloric acid than those of Van Diemen's Land; and further, in the final determination of the constituents, the analysis shows a larger quantity of alkalies and salts in the soils of greater solubility, and a larger quantity of silica in those of lesser solubility.
In their external character, the soils of New South Wales and Van Diemen's Land are, nevertheless, alike; particularly those which are as yet untouched by the hand of man, and which possess, in both colonies, the same degree of softness, coherence, and porosity common to all virgin soils, together with a low specific gravity, and a proportion of organic to inorganic matter amounting to a third, and in one instance to a half, of the whole quantity. *
Compared with the virgin soils which the writer has examined in Canada, the United States, Brazil, the Argentine republic, Guatemala, Mexico, and the islands of Bailly and Lumbock, those of New South Wales and Van Diemen's Land are greatly inferior in
the amount of salts and alkalies they contain, and therefore in fertility.
To that comparatively low productive power of soils, there is nevertheless an indigenous vegetation,— luxuriant, healthy, and vigorous in its kind,—most admirably adapted to it; the Australian graminae, which are tufted and delicate, and which yield an excellent support to animal life, show by incineration, that they do not contain the same quantity of alkalies as the English grasses, and therefore do not need a very rich soil for passing luxuriantly through all the stages of developement. The family of Eucalyptce, likewise, which flourish all over the country, are most wonderfully adapted to it; as, by shedding their bark, the Eucalyptce can dispense with the annual supply of alkalies which trees shedding their leaves would have extracted from the soil.
This wonderful adjustment of the organic to inorganic matter has been, nevertheless, disturbed: the same agency of civilisation which, as has been already shown, modified the nature of the normal climate of the two colonics, changed likewise the physical and the chemical property of their respective soils.
From the circumstance that, on the first introduction of tillage and grazing, the analysis of soils in particular fields was not performed, and the chemical nature of the first seed and the first crop not ascertained, it is difficult to determine the precise extent of this change, as regards soils. Judging, however, from the constituents of those untouched by the hand of man, the soils under tillage or pasturage have deteriorated in an agricultural point of view, having lost in salts and alkalies. Furthermore, they have deteriorated in a climatic point of view, as their power of absorbing moisture from the atmosphere has been curtailed, and that of absorbing solar heat has increased; while that of retaining heat, during terrestrial radiation, has decreased.
Be it however remarked, that the influence of civilisation, here spoken of, partakes more of the character of those unavoidable results which attend the transition epoch of all human progress, than of those ultimate effects of civilisation which, as regards Terra Australis, need as yet time and means ere they can be fully developed, and rendered ripe for a just appreciation of the civilising influence.
CLASSIFICATION OF SOILS.
The varieties of soils which are observed in the two colonies, may be traced not only to the kind of rocks characteristic of each colony, but to their respective configuration, and to the greater or lesser denudation and renovation of the surface, consequent upon that configuration.
Throughout the greatest portion of New South Wales and Van Diemen's Land, the fine and most valuable ingredients yielded by the rocks and vegetation, in the process of their decomposition, are generally carried away from their original sites by the rain-water. If the floor which is disintegrating is composed of siliceous rocks, the surface subject to denudation retains only that portion of silex and silicates which, from their specific gsavity, have resisted the action of the water-current; and, in that instance, it presents a deposit of loose and sterile constituents.
If the surface happens to be intermixed with conglomerates or sandstone, the alternate disintegration and denudation produces a hard floor, in the crevices of which the Banksia and a dwarfish Eucalyptce can alone flourish. At times, that floor is covered with fragments of conglomerates or coarse sandstones, which have resisted the action of water, and against which a drift of siliceous with some aluminous earth is found accumulated. When, on the other side, the surface is composed of trappean rocks, or, when such are found near to it, a continual transformation of the protoxide of iron (in which the rocks have been shown to abound) into peroxide equally checks the growth of vegetation; and in that case, on an apparently rich reddish tract of hills, nothing but a scanty and stunted vegetation of Mimosa; is to be seen. The most remarkable exemplification of this, is in that portion of Cumberland (Van Diemen's Land) which lies to the north of Hamilton.
When, however, ridges or hollows lie.in the way of the drift, the deposits from the upper country are found either lodged against the slope of the hills, or accumulated in basins and flat-bottomed valleys.
The sudden condensation of vapours in New South Wales, and their gradual condensation in Van Diemen's Land, have been pointed out, in Section III., as meteorological facts which distinguish the respective climates of these colonies. Their effects, as bearing upon the question before us, are obvious; and thus, in New South Wales, the denudation may be safely inferred to be greater, and more injurious to the country, than it is in Van Diemen's Land.
From what has been said, it follows that the soils of the two colonies consist of two distinct classes, within which all the minor varieties may be included: the first, impoverished by denudation, and which yields only pasture for grazing; the last, enriched by the drift, presenting every inducement for agriculture.
We shall now consider, in turn, each of these classes of soil, and the kind of industry employed to render available their respective powers of production.