THE STORY OF THE SOIL

Hawke's Bay Tribune, Volume XXII, Issue 174, 8 July 1932, Page 11

THE STORY OF THE SOIL

HOW IT IS MADE. The study of soils and their properties may be regarded as an essential part of the gardener’s education, and though at first sight this may appear an unpromising subject for many, it will be found that when once the matter is shorn of repcllant technicalities, its interest equals its practical importance.

To start at the beginning, it is necessary to glance briefly at the manner in which soil, as the cultivator understands the term, is formed. Perhaps the best way to obtain a clear idea of its origin is to examine the face of a cliff or the exposed side of a quarry, considering the different layers of earth seen from the top downwards. First comes the band containing the roots of plants growing on the surface, which will vary in thickness according to the district in which the observation is made. Characteristic of this top layer is its dark colour and fine texture. Next comes a lighter and more lumpy area, into the upper portion of which some of the larger roots penetrate, the line of demarcation between the two bands being ill-defined, though tho differences of the more central parts arc striking enough. This is tho sub-soil. It is considerably deeper than the surface layer and grades off gradually into the next section, which is of hard,' solid rock. Originally the whole of the cliff face was composed of the hard rock, but owing to tho destructive action of frost and heat, wind and rain, tho upper parts have been broken up into fragments of varying sizes, the topmost layer, being the one most exposed, having suffered most in this way. At one time in tho world’s history, the whole of the surface was composed of rocks like granite, basalt, and lava. Those have been slowly broken up under the age-long action of rain, wind and sea, and the resulting fragments carried away by water to bo again deposited beneath the aneient oceans. In the course, of time these accumulated deposits have boon raised up to form

new land surfaces, and now constitute our “sedimentary’’ rocks —limestone, standstones, clays, etc. And just as the weathering of different kinds of materials in these rocks resulted in the formation of various types of sedimentary deposits, so the breaking up of the latter has given us soils of quite different properties and chemical composition.

Tho fact that weather exerts a destructive influence on solid stone is from time to time brought home to us in no uncertain way. The outer fabric of our public buildings—as cathedrals and the Houses of Parliament —has to be renovated and patched up periodically owing to the crumbling away of the stone under the action of rain, wind and fog, and it does not need any great effort of the imagination to picture what would bo the fate of these edifices if they were left unrepaired for a few centuries.