Agricultural geology . Fig. 36. A vertical dyke of impervious igneous rock, cutting across inclinedstrata, causes a spring at S by holding up the water in the pervious (dotted)stratum to the left. strata are generally impervious and may originate an accumu-lation of water, with outflow of a spring, in the middle of apermeable series (see Fig. 36). Again faulting may give riseto favourable conditions, by bringing impervious strata agaiastpermeable ones, and so forming a basin. The conditions here VIl] WATEK SUPPLY AND DRAINAGE 171 may somewhat resemble those necessary for an artesian well,to be
Agricultural geology . Fig. 36. A vertical dyke of impervious igneous rock, cutting across inclinedstrata, causes a spring at S by holding up the water in the pervious (dotted)stratum to the left. strata are generally impervious and may originate an accumu-lation of water, with outflow of a spring, in the middle of apermeable series (see Fig. 36). Again faulting may give riseto favourable conditions, by bringing impervious strata agaiastpermeable ones, and so forming a basin. The conditions here VIl] WATEK SUPPLY AND DRAINAGE 171 may somewhat resemble those necessary for an artesian well,to be presently described. In point of fact the possible varia-tions are endless, and no good purpose would be served by afurther detailed consideration of Kg. 37. Spring due to faulting of inclined strata. The permeable (dotted)bed is brought by the fault F against an impervious bed, and water isheld up in it, till it rises to the point S, where it overflows as a spring. Wells. The essential feature of a well is that it must cutthe water table or upper limit of saturation. If this conditionis fulfilled the portion of the well below this level will be per-manently filled with water. The conditions may even be suchthat the water rises to the surface, or even above it as a are called flowing or artesian wells. More commonlyhowever the water has to be brought to the surface by a bucketand rope, or by a pump. If the level of the water is not morethan about 30 feet from the surface the common suction pumpmay be used; beyond this depth it must either be brought uplaboriously by dipping and winding, or by some sort of forcepump, or ram. For this purpose windmills are very commonlyemployed, being both cheap and effective. In choosing th
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectgeology
