As the distances of drains apart, depend manifestly on many circumstances, which may widely vary in the diversity of soil, climate, and cost of labor and materials to be found in the United States, it will be convenient to arrange our remarks on the subject under appropriate heads. DISTANCES DEPEND UPON THE NATURE OF THE SOIL. Water runs readily through sand or gravel. In such soils it easily seeks and finds its level. If it be drawn out at one point, it tends towards that point from all directions. In a free, open sand, you may draw out all the water at one opening, almost as readily as from an open pond. Yet, even such sands may require draining. A body of sandy soil frequently lies not only upon clay, but in a basin; so that, if the sand were removed, a pond would remain. In such a case, a few deep drains, rightly placed, might be sufficient. This, however, is a case not often met with, though open, sandy soil upon clay is a common formation. Then there is the other extreme of compact clay, through which water seems scarcely to percolate at all. Yet it has water in it, that may probably soak out by the same process by which it soaked in. Very few soils, of even such as are called clay, are impervious to water, especially in the condition in which they are found in nature. To render them impervious, it is necessary to wet and stir them up, or, as it is termed, _puddle_ them. Any soil, so far as it has been weathered--that is, exposed to air, water and frost--is permeable to water to a greater or less degree; so that we may feel confident that the upper stratum of any soil, not constantly under water, will readily allow the water to pass through. And in considering the "Drainage of Stiff Clays," we shall see that the most obstinate clays are usually so affected by the operation of drainage, that they crack, and so open passages for the water to the drains. All gravels, black mud of swamps, and loamy soils of any kind, are readily drained. Occasionally, however--even in tracts of easy drainage, as a whole--deposits are found of some combinations with iron, so firmly cemented together, as to be almost impenetrable with the pick-axe, and apparently impervious to water. Exceptional cases of this nature must be carefully sought for by the drainer. Whenever a wet spot is observed, seek for the cause, and be satisfied whether it is wet because a spring bursts up from the bottom; or because the subsoil is impervious, and will not allow the surface-water to pass downward. Ascertain carefully the cause of the evil, and then skillfully doctor the disease, and not the symptoms merely. A careful attention to the theory of moisture, will go far to enable us properly to determine the requisite frequency of drains. DISTANCES DEPEND UPON THE DEPTH OF THE DRAINS.