Should any rock strata be vertically inclined instead of horizontal, although it may be known in the latter case they are generally watertight, fissures in the upheaved beds may become channels for the passage of the subsiding or rising waters, and may cause saturation of the soil over a considerable area and induce a flow through the slopes or the seat of an embankment. Upon such a site no reservoir, dock, canal, or any earthen structure to hold water should be placed; but although the nature of the ground may be fatal to the stability of such an embankment, so long as the underground waters do not rise to the level of the seat of a railway embankment or flood a cutting or burst the slopes, they may not seriously affect the stability; for, unless the head level of supply is great, more danger maybe expected from downward percolation saturating the ground upon which the embankment is placed than from an upward flow. The insecurity of erecting a reservoir or similar work upon such a site, in which water is brought into a district in greater quantity than its natural flow, is obvious, as the earth may gradually become saturated from the constant leakage down the upheaved fissures, until it becomes in an unstable condition and finally slips and subsides. CHALK. As in most public works, with the except:on of tunnels, wells and mines, the chalk with which an engineer has to deal is surface chalk, or the top layers of that deposit known as the upper chalk, almost invariably containing much more water than the lower chalk, although it rises quicker in the lower beds, as it is under greater pressure, and which vary in hardness, purity, and solidity and may have frequent fissures and holes, with or without flints, and be anything from hard, compact chalk rock to mere marly calcareous earth; considerable judgment is required to successfully determine the slope of stability and the precautionary works that may be necessary to attain repose; for some of the upper beds soon weather, and being soft, friable, and fissured are permeable and liable to slip; in fact, the Oolitic series, as it consists of alternating bands of limestones and clays and occasionally sandstone, is frequently fissured and has loose joints and therefore requires to be carefully treated. The range of the slope of permanent stability obviously depends upon the nature of the chalk, whether it is denuded or covered or mere loose-jointed strata, the effect ground and surface waters may have upon it, and also the position of the beds, and whether a cutting or embankment is on the side or the base of a hill, and consequently at the place where it is likely to be in a wet condition.