The Farm.

New Zealand Tablet, Volume IX, Issue 454, 23 December 1881, Page 23

The Farm.

Ouß Soils. — Professor Huxley once wrote a capital lay sermon upon a lump of chalk. An equally good sermon might be preached upon a clod of earth, and this fact has been pressed upon us more strongly than ever by the appearance of Mr. Darwin's work upon earthworms. The great naturalist has added another side from which we may view the raw material of our fields, and exhibited to us yet another natural force which has tended towards the formation of fertile soils. Perhaps few farmers trouble themselves nruch as to the origin of the soils they till. It is enongta for them that they can produce so many sacks of wheat or tons of roots. But the origin of anything is always a point of interest, and that of our soils especially fo, as they lie close at the very foundations of life itself. As every living thing returns to the earth, 60 also is the earth in a secondary sense the mother of us all. If we wish to know how good and bad land, clays and sands, chalks ana peats were formed, we i must ask the geologist. That they were formed and had a beginning is certain, so that we must not for a moment think that soil has always existed. Far from it. We know hovy it came into existence, and from what sources it was derived. If we examine a soil we find that it is composed of loose, darkcoloured material, interspersed with mineral fragments of greater and lesser size. The Dature of the soil will be found to vary with the situation in which it is found and from whence it is taken. If it is i removed from the slopes of a chalk hill it will be found chalky in its j character ; if from a district in which the underlying rock is red j sandstond it will be found to be red, and to partake of the nature of the rock. Investigation clearly points to the fact that all soils have been derived from rocks, and that they are loose and crumbling I because they are decayed and broken down rocks. The hard intractable mass, whether of granite or bard sandstone or softer chalk or clay, is the first stage. These rocks are acted upon through countless years by certain natural forces, -under which they break down, and finally are converted to soil. Anyone who examines the loose matter which accumulates at the base of quarries and precipices will see examples of soils now forming. The way ia which this important work of soil manufacture is carried out in nature's laboratoiy may be thus described — A hard rock is exposed for years to the action of the air, of moisture and of changes of temperature. The air, being charged with a small proportion of carboDic acid gas, acts in conjunction with water. There is formed by this union a very weak solution of carbonic acid in water, which is a solvent under whose action the hardest rocks will at length give way. Minute as the effect raay be, it gradually decomes manifest by the erosion of the surface and the effacement of tool marks or inscriptions. This effect is further increased by the action of alterations of temperature from ■, frost to thaw. The expansive power of water when it changes from the liquid to the solid state is well known. It is the cause of many phenomena, and explains the beneficial action of frost to arable land. The same force is very destructive to building stones, to brickwork, and to drainage tiles. It is the cause of landslips, and to it is due the weathering of rocky surfaces and the crumbling of the faces of quarries. Another disintegrating force of even greater power is that of running water. Mountain streams wear through the hardest rocks and form gorges of terrific depth. If the question is asked, what has become of the vast quantity of matter worn away by tens of thousands of mountain and lowland streams ? the answer is, that it has gone to form tracts of fertile soil in the valleys beneath. Ice is a great wearer of rocks when it is massed together in the form of glaciers, and grinds down the mountain gorges which hold it. The rearing and grinding action of ice is well known to all tourists. The action of these forces has, no doubt, resulted in the formation of soils. In some cases they have been applied in such a manner as to simply disintegrate the surface and yield a soil intimately related to and derived from the rock which underlies it. In other cases they have been so applied that the resulting soil has been transported as fast as formed to a distance. Kunning -water is the agent by which this transportation is effected, and as & result we find deposits of rich soil in valleys, and along the banks and at the estuaries of rivers. — Agricultural Gazette.