If it could be determined at what depth in any earth in any state percolation, evaporation, and meteorological influences would cease, and also their effects, rules could be deduced for guidance in draining cuttings and embankments. The manner of the execution of ordinary cuttings and embankments is so dissimilar to that of filter-beds of waterworks, that the experiments made for such purposes are only of comparative value for the former works, for the condition as well as the character of the soil affects its permeability by water. For instance, in cuttings, with the exception of some surface disturbance during the process of excavation, the removal of vegetation or a covering, and the exposure of the ground to the atmosphere, &c., the normal state of the earth is not much altered; but in embankments different soils may be intermingled in a manner almost unknown in nature, the varieties of mixtures of earth being most numerous, and they may be in every condition of compactness, dryness, and dampness amounting almost to saturation, and in any case, therefore, percolation is temporarily or permanently increased consequent upon the earth having been disturbed and loosened. The general principles of the percolation of water are here only briefly referred to, as they particularly concern slips in earthwork: but obviously the quantity of percolated water greatly affects the stability of a slope, for the surface water should not be guidelessly allowed to soak into or be absorbed by the ground at the top, and so proceed through and down the slopes, as then the pent-up water tends to press out the face which may be temporarily sun-dried. As in excavating cuttings the surface is bared and vegetation removed from the soil, water has easier access, and unless the ground when excavated is immediately covered as before, its normal state is not preserved. One point of considerable importance is to ascertain whether in any cutting or embankment percolation is uniform and regular; some infiltration will necessarily take place, as water will gravitate from the top to the bottom and will find the easiest course or line of least resistance, which may not be at the lowest level.