AGRICULTURAL GEOLOGY.

Dunstan Times, Issue 1213, 29 May 1885, Page 3

AGRICULTURAL GEOLOGY.

By W. Green;

Geology throws much light on the prospects of agriculture. In its investigations among the rocks, it discovers with considerable exactness the agricultural and miaera' value of a country. The rocks which form the crust rf the earth are composed of two classes—the greater part called sedimentary (formed by water), and the lesser termed igneous (fprin'-d by tiro). The sedimentary rooks have been deposited in beds called strata, which are found to be in a regular order of g‘adation from the lowest to the h'ghest. The igneous rocks have been formed in the profound depths of the earth, and thrust up to the surface by the action of tire, and are mountains, or in wall-like masses termed "dykes ” It is chiefly with the sedimentary rocks that we have to do, and these are slates, sandstones, and limestones. In giving this subject a

practical issue,;! shall first on THE NATURE AND ORIGIN OP SOILS That coating of loose earth which lies * beneath our foot, and which wo know covers' the solid rock almost everywhere, we call soil, though perhaps this is not at ah times the proper term for it. If we dig down through this loose |earth we shall come sooner or later to the hard rook ; and we shall most likely find the earth next to the rock coloured with and composed of fragments of the rook. And if we happen to I live in a district where the rocks appear | above the surface of the ground, as in mountain ranges, we shall doubtless see lying about the aides*of the mountains large fragments of rock which may be easily traced to the original bed from which they have became detached. Year by year those rocks grow less, through the disintegrating influence of the fronts and winds of each succeeding winter, and Anally are crumbled to dust and washed away by ,the rains to the valleys and plains below. By this crumbling or decay of the rocks the soil is made. . £Vom what we have seen it will be easily inferred that the character of a soil will bear a strong . relation to the mineral character of the rocks of the neighbourhood. Thus, upon the slate rocks we shall find a clayey soil; upon the sandstone a sandy soil; and. upon the limestones a calcareous soil or loam. In either case* the peculiar character given to the soil is more noticeable when the same rock formation prevails through some extent of coun ry. Where this uniformity of rock covers very large areas, ir. is sure to lead to a barreuess of the soil. Rocks which do not readily break up and pulverise under atmospheric influences, will have but a scanty covering of soil upon them, and those also deficient in the principal mineral elements required for the support of vegetation will make a barren soil anywhere, for example, on the chalk downs and the granite moors of the Old Country. When two rocks of different characters, as a sandstone, and a bed of clay outcrop together in a field or paddock, the S'nl will oe very much richer near the junction line of the two beds than it will be some di i tance away, because the particles of she unproductive sandstone become mingled with the stiff clay, and render it a loose loamy soil. Taking examole by this fact, the farmers m certain parts of England cart the chalk on to the clay lands for manure. In most situations rocks yield their own peculiar coloring to the soil. In the mid land counties of England, where the car boniferons system prevails, ‘ the change in the strata is very frequent, and often reveals itself by a vanegated appearance of the soil in the ploughed fields. (To be continued).