The chief objection to open drains is that all excavated trenches or inserted drains in the slopes destroy the cohesion of the earth and aid in detaching portions of the surface. If the cohesion and adhesion of the soil were the same under every condition, this would be a cogent reason against the system, but, as in earthwork, every degree of moisture from dampness to saturation may be attained, the cohesive power is a very variable quantity, apart from the effects of vibration; and also open drains undoubtedly do cause a slope to be drier, and moderate local humidity, and therefore increase the cohesion and general stability of the part drained; the only fear being that from inattention they may become choked; then they are dangerous, as they will permanently collect and retain water instead of temporarily retaining and gently guiding it. A careful consideration of the circumstances may much reduce this objection by indicating whether it is advisable to have only a few deep, or several small surface drains. Provided proper precautions are taken, experience indicates that filled-in trenches in the slopes are generally successful, and certainly are simpler and cheaper than a retaining wall at the toe of a slope. In pervious soil it may be economically impossible to drain the slopes unless they are divided into sections, and should the material in the trenches be well-packed and pressed down, it may even increase the friction between the separated portions. In connection with the drainage of cuttings may be named that excavation should not be allowed to be cast upon the cess unless some distance from the edge of a slope, and only temporarily for purposes of ballasting and metalling; as such spoil-banks increase the load and localize the water to be drained. A more complete system of drainage may be necessary than those previously named, consisting of a combination of wells, open, or holding filtering material; pipe-drains or filled-in trenches, wells with a pipe leading to a catchwater drain, &c., or other usual methods of land drainage. For instance, it may be discovered that water issues from a spring outside the fence or cutting; if so, in order to drain the slopes it may be necessary to sink a well to a stratum below the formation level so as to tap the spring, thereby preventing an exudation of water upon the slope; this is a better plan than drawing the water into the slope and then draining it. When pervious earth overlies an impervious stratum, _i.e._, gravel or sand upon clay, rough-filled wells at intervals inside the fence extending 3 or 4 feet into the clay, with an outlet drain, may be required to prevent a flow of water upon the clay and a wetted surface upon which the gravel can slide; and it may be necessary to have a cess on the slope between the top of the clay and the bottom of the gravel or sand, with a catchwater drain upon it, particularly in a cutting in sidelong ground.