"Sometimes the strata are disposed in the form of a basin. In this case, the water percolating through the more elevated ground--near what may be called the rim--collects in the lower parts of the strata towards the centre, there forcing its way to the surface, if the upper impervious beds be thin; or, if otherwise, remaining a concealed reservoir, ready to yield its supplies to the shaft or boring-rod of the well-sinker, and sometimes forming a living fountain capable of rising many feet above the surface. It is in this way that what are called Artesian wells are formed. The following diagram represents such a disposition of the strata as has just been referred to. The rain which falls on the tracts of country at A and B, gradually percolates towards the centre of the basin, where it may be made to give rise to an Artesian well, as at C, by boring through the superincumbent mass of clay; or it may force itself to the surface through the thinner part of the layer of clay, as at D--there forming a spring, or swamp. [Illustration: Fig. 8.] "Again: the higher parts of hilly ground are sometimes composed of very porous and absorbent strata, while the lower portions are more impervious--the soil and subsoil being of a very stiff and retentive description. In this case, the water collected by the porous layers is prevented from finding a ready exit, when it reaches the impervious layers, by the stiff surface-soil. The water is by this means dammed up in some measure, and acquires a considerable degree of pressure; and, forcing itself to the day at various places, it forms those extensive "weeping"-banks which have such an injurious effect upon many of our mountain-pastures. This was the form of spring, or swamp, to the removal of which Elkington principally turned his attention; and the following diagram, taken from a description of his system of draining, will explain the stratification and springs referred to, more clearly. [Illustration: Fig. 9.] "In some districts, where clay forms the staple of the soil, a bed of sand or gravel, completely saturated with water, occurs at the depth of a few feet from the surface, following all the undulations of the country, and maintaining its position, in relation to the surface, over considerable tracts, here and there pouring forth its waters in a spring, or denoting its proximity, by the subaquatic nature of the herbage. Such a configuration is represented in the following diagram, where A represents the surface-soil; B, the impervious subsoil of clay; C, the bed of sandy-clay or gravel; and D, the lower bed of clay, resting upon the rocky strata beneath. [Illustration: Fig. 10.]