In the letter of Mr. Denton, in another chapter, some remarks will be found upon the subject of which we are treating. The same gentleman has, in a published paper, illustrated the impossibility of strict adherence to any arbitrary rule in the distances or arrangement of drains, as follows: "The wetness of land, which for distinction's sake, I have called 'the water of pressure,' like the water of springs, to which it is nearly allied, can be effectually and cheaply removed only by drains devised for, and devoted to the object. Appropriate deep drains at B B B, for instance, as indicated in the dark vertical lines, are found to do the service of many parallel drains, which as frequently miss, as they hit, those furrows, or 'lips,' in the horizontal out-crop of water-bearing strata which continue to exude wetness after the higher portions are dry. [Illustration: Fig. 35.--The vertical dotted lines show the position of parallel drains.] "A consideration, too, of the varying inclinations of surface, of which instances will frequently occur in the same field, necessitates a departure from uniformity, not in direction only, but in intervals between drains. Take, for instance, the ordinary case of a field, in which a comparatively flat space will intervene between quickly rising ground and the outfall ditch. It is clear that the soak of the hill will pervade the soil of the lower ground, let the system of drainage adopted be what it may; and, therefore, supposing the soil of the hill and flat to be precisely alike, the existence of bottom water in a greater quantity in the lower lands than in the higher, will call for a greater number of drains. It is found, too, that an independent discharge or relief of the water coming from the hill, at B, should always be provided, in order to avoid any impediment by the slower flow of the flatter drains. [Illustration: Fig. 36.] "Experience shows that, with few exceptions, hollows, or 'slacks,' observable on the surface, as at B B, have a corresponding undulation of subsoil and that any system which does not provide a direct release for water, which would otherwise collect in and draw towards these spots, is imperfect and unsatisfactory. It is found to be much more safe to depend on relief drains, than on the cutting of drains sufficiently deep through the banks, at A A, to gain a fall at a regular inclination.