When we have thus disposed of the water from the surface-flow, the shallow springs and the deep springs, and given vent to the water accumulated and ponded in the low places, we have then accomplished all that is peculiar to this kind of drainage. We have still the water from the clouds, which is twice as much as will evaporate from a land-surface, to provide for. We assume that this cannot pass directly down by percolation, because the subsoil is already saturated; and therefore, even if all the other sources of wetness are cut off, we shall still have a tract of land too wet for wheat and corn. If the swamp be very small, these main ditches may sufficiently drain it; but if it be extensive, they probably will not. We have seen that we have some eighteen or twenty inches of water to be disposed of by drainage; so much that evaporation cannot remove consistently with good cultivation; and, although this amount might, in a very deep peaty soil, percolate to a great distance laterally, to find a drain, yet in shallow soil resting on a retentive subsoil, drains might be necessary at distances similar to those adopted on wet upland fields. To this part of the operation, we should, therefore, apply the ordinary principles of drainage, putting in covered drains with tiles, if possible, at four feet depth or more, ordinarily, and at distances of from forty to sixty feet, although four-foot drains at even one hundred feet distance, in peat and black mud, might often be found sufficient. Through the kindness of Edmund Ruffin, Esq., of Virginia, we have been furnished with three elaborate and valuable essays, on the drainage and treatment of flat and wet lands in lower Virginia and North Carolina, published in the Transactions of the Virginia State Agricultural Society, for 1857. The principal feature of his system is based upon his correct knowledge of the geological formation of that district; of the fact in particular, that, underlying the whole of that low country, there is a bed of pure sand lying nearly level, and filled with water, which may be drawn down by a few large deep drains, thus relieving the surface-soil of surplus water, by comprehensive but simple means.