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laws disturbs, in assuring us that "nothing is more certain than the fact, that a District or State which exports largely the things which Nature demands to form breadstuffs and provisions, must sooner or later export also some of its consumers of bread and meat;" while the reward of obedience is "that a State can feed and clothe a

population ten times larger at home than abroad." We can see no reason in the nature of things, why the disproportion should be set at so low a figure; for it is impossible to conjecture a limit to the increase of population, if man will but conform to the law which Nature exemplifies in all her processes, by which the soil regains whatever material of nutriment it has lent for the support of vegetable and animal life, and that with large interest, derived from the elements furnished by the atmosphere, and incorporated in the substance of the matter, which, on the extinction of its vitality, returns to the bosom of the earth.

Having thus cursorily stated the general laws which operate in the cycle of animal and vegetable life, independent of human agency, we are prepared to follow the steps by which the soil is prepared for the theatre of human labour, and the successive stages which mark man's progress in obtaining food, and in supplying the other wants, the pressure of which is felt, the moment the primary want of his vegetative nature is satisfied.

Those who desire to study the laws which have been the subject of this chapter, will find abundant information in the works of Liebig, and the treatise of Professor Johnston on Agricultural Chemistry. The lectures of the latter gentleman before the New York State Agricultural Society, together with the Prize Essay of Professor Norton on Agricultural Chemistry, which elucidate the subject sufficiently for general readers, may be found in the volume of its Transactions for 1849, which is widely distributed through the State, and readily accessible. Professor Emmons's work on the Agriculture of New York, forming two volumes of the series of its Natural History, is also generally accessible.

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CHAPTER II.

THE FORMATION OF SOILS, AND THEIR ADAPTATION TO OCCUPATION AND CULTURE.

THE coral islands of the tropical seas present the most remarkable examples of the rapid clothing of a naked rock with vegetable life, and its preparation for the habitation of human beings. The creatures which build up these islands from unknown depths in the ocean, partake, as is indicated by the name of their species, zoophyte, or animal plant, in the characteristics of both orders of vitality. They fulfil their functions without a heart or system of circulation—the several polypi in a group have separate mouths and' tentacles, and separate stomachs; but beyond this there is no individual propertyand form a living sheet of animals, fed and nourished by numerous mouths and stomachs, but coalescing by intervening tissues. They possess no more power of motion than is sufficient to thrust out their arms to seize the food that drifts past them, and they propagate by buds, the bud commencing as a slight prominence on the side of the parent: the bud enlarges, a circle of tentacles grows out, with a mouth in the centre, and the enlargement goes on till the young equals the parent in size, when it begins to protrude buds itselfand the group thus continues to grow. They secrete the coral as the quadruped secretes its bones, until single reefs are formed and attain the surface of the water. But it is essential to the life of these submarine builders that they should be covered by the waves, and when they have reached low water mark they die. A new process now begins, in the accumulation of loose materials upon its summit, from coral boulder-broken off from the reef by the waves, thrown up from below, and gradually ground into fragments—coral gravel and sand. Agassiz states that all that portion of Florida known as the Everglades is only a vast coral bank, composed of a series of more or less parallel reefs, which have successively grown from the bottom of the sea up to the surface, and have been added to the main land, by the gradual filling of the intervals which sepa

rate them with deposits of the coralline sand, and debris brought thither by the action of the tides and the currents.

The cocoanut, with its husk, being well adapted to be wafted by the waves, it takes root upon the naked sand of the coral island, just lifted above the level of the ocean, and, washed by the spray, grows luxuriantly." Nourished at first by only so much of organic aliment as the remains of the zoophytes, who built the island, supply, the decay of its leaves soon furnishes a mould which suffices for other vegetable growth. Its uses are manifold: the inhabitants, when they come, find in it material for the scanty dresses which the climate requires, drinking-vessels from the shell of its nut, and other utensils, mats, cordage, fishing-lines, and oil, besides food, drink, and building materials. In every stage, from its first formation after the fall of the blossom, to the hard, dry, and ripe nut, that has almost begun to germinate, the fruit may be seen at the same time, on the same tree. The pandanus, or screw-pine, another tree which soon roots itself in the scanty soil, throwing out props from the trunk, which plant themselves in the ground, and widen the supporting base as it grows, furnishes a sweetish, husky fruit, "which, though a little bitter," says Mr. Dana, in his Geology of the Exploring Expedition, from which these facts are drawn, "admits

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* "How are the seeds of plants brought so immediately to these new shores? by wandering birds, or by the winds and waves of the ocean? The distance from other coasts makes it difficult to answer this question; but no sooner is the newly-raised island in direct contact with the atmosphere, than there is found on its surface, in our northern countries, a soft, silky net-work, appearing to the naked eye as coloured spots and patches. Some of these patches are bordered by single or double raised lines running round the margin; other patches are crossed by similar lines, traversing them in various directions. Gradually the light colour of the patches becomes darker, the bright yellow, which was visible at a distance, changes to a brown, and the bluish-grey of the lepraides becomes a dusty black. The edges of neighbouring patches approach and run into each other; and on the dark ground thus formed there appear other lichens, of circular, shape and dazzling whiteness. Thus, an organic film or covering establishes itself by successive layers; and as mankind, in forming communities, pass through different stages of civilization, so is the gradual propagation and extension of plants connected with determinate physical laws.”; Humbold

of being stored away for food when other things fail." Fish and crabs from the reefs, and the large fish caught with wooden hooks from the deep waters, eke out the subsistence of the natives. "From such scanty resources," says Mr. Dana, "a population of 10,000 persons is supported on the single island of Taputeouea, whose habitable area does not exceed six square miles."

The process in this case, by which the emerging peak of the submarine mountain is fitted by the germination of vegetation for a human abode, is rapid. That by which the peaks of the land mountain have crumbled into soil involves more intermediate stages, and a much greater variety of results. Some of the rocks, such as slates and shales, decompose with such facility, that the whole process may be observed within a brief period, and we have constant opportunities of watching its progress. The granitic rocks, however, which, constituting in the view of geologists the lower and earlier strata, have been made, upon the disruption and upheaving of the crust of the earth, to occupy the highest place, are of a less frangible character. But their chemical composition is, such as to favour their speedy disintegration under the action of the elements. The presence of alkalies in the feldspar and mica, which are combined with silex in granite, exerts a powerful influence in this change. Carbonic acid, the great solvent for the hardest materials, decomposes the potash with which silica is combined in the feldspar, and it is made soluble. The intensity of the frost, and the length of time during which rocks on the mountain tops are exposed to it, the suddenness of the changes of temperature to which they are subjected, and which, from their being poor conductors of heat, involve an inequality in the contraction and expansion of the surface and the interior, which induces flaking and cracking, the dampness of the air during the summer, when watery vapours condense upon their summits, are among the circumstances which hasten the destruction of rocks in these places. As disintegration is accomplished by the process of weathering, the decomposed particles fall by their own weight, and are washed by the rains into the valleys beneath, which receive in the same manner the contributions of the intermediate rocks. During this process the rocks are not merely mechanically broken into small fragments, but from their insoluble constituents,

soluble salts, as those of lime, soda, &c., are generated, which may be absorbed by the roots of plants. In the decomposition of feldspar, the silicate of potassa is gradually removed by the water, and while the sand remains upon the sloping surfaces, the fine alumina or clay accumulates in the valleys, and forms a mixture of clay and sand, which is more favourable to the support of grass and grain. Thus every gradation is presented, from the naked granite of the hill-tops, through the thin, porous soils of the slopes, to the rich meadow lands of the valleys.

Vegetation of some kind, however, can find nourishment even on the surface of the rock. Lichens and algæ grow high above the line of perpetual snow; and in bleak northern climes, upon the bare face of the granite rock, a species of lichen flourishes, which the hungerpinched Canadian voyageur seeks for food, and gives the appetizing name of "tripe de roche." Decaying vegetable matter of such kinds is swept by every shower down hill, to accumulate at the base with the deposits of mineral origin. After a sufficient period a soil is thus formed at the bottom of the slopes, which is capable of sustaining heavy timber. The first tree sheds its leaves and branches to feed the fattening soil, in a circle around its trunk, whose area is measured by the spread of its branches. The probable process from this starting point is this: Upon the outer circumference of the first circle thus nourished, and that edge of it, which, lying between the trunk and the hill-top, upon the ascending slope, is inferior to the lowest point in the collected elements of vegetable nutrition, it becomes possible for another tree to grow. This, in its turn, becomes the centre of a circle of fertilized ground, upon whose upper exterior the material to support a new growth is accumulated, by the droppings of its stem and branches. Each new plant thus manures the ground for its successor, and vegetation creeps up the hill-side, along a soil of constantly diminishing richness, and which, though made more fat and tenacious by its own growth, is always parting with some portion of its mineral and vegetable elements to fatten the valley beneath it.* The process, like so many others in the opera

* "The plantations of the late Duke of Athol consist chiefly of white larch, and grow upon a poor, hilly soil, resting on gneiss, mica, slate, and

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