Sand, dry river │ 0·041 │ 1·10 Sand, damp and shaken │ 0·055 │ 1·50 Sandstone, solid │0·063 to 0·072 │ 1·70 to 1·95 Shale │ 0·074 │ 2·00 Slate, solid │ 0·080 │ 2·15 Trap, solid │ 0·078 │ 2·10 ───────────────────────────────────────┴───────────────┴─────────────── In determining the safe load upon deposited earth it is well to remember that: 1. Excavated earth cannot be restored in bulk to its original condition. 2. When the earth is simply deposited from a tip head, it cannot be immediately consolidated by the act of deposition. 3. Until subsidence may, for all practical purposes, be considered at an end, no deposited earth can be regarded as stable; but a mere uniform weathering of the surface, which cannot be prevented when the exterior is uncovered, will generally not cause instability of the mass. 4. Upon most public works the earth in an embankment is exposed in thin layers. 5. The earth is loaded, in the great majority of cases, soon after it is deposited and before it has settled or become consolidated, and is also subject to vibration from earth waggons, locomotives, &c. 6. The comparative dry or wet state of the deposited earth and its power of resistance to meteorological deterioration. _Vide_ also Chapter IX. Taking into consideration these and other deteriorating influences, the problem to be solved is, what deduction must be made from the safe load upon unexcavated earth in foundations, in order to know the safe sustaining power of the same earth when deposited in an embankment? Much depends upon the liability of the soil to become saturated or in a damper state than that in which it is known to be stable. For this reason the height of embankments in clay soils, which are so deleteriously affected by the weather, is generally made as little as possible. Of course, temporarily an embankment will stand with a greater pressure, _i.e._, at a greater height than the safe height, and, provided no lateral movement took place, an embankment would be stable until the earth was nearly crushed; but permanent stability and freedom from slips and subsidence is the object to be attained, and everything must be subject to local conditions, such as the amount of rainfall, the situation, the care exercised during deposition, the protection given to the surface, and the general drainage, and these must always govern the application of any general rule. It is, therefore, necessary to divide earths into two kinds, namely:—granular and non-granular; the former is assumed to have particles, for purposes of earthwork, insoluble in water, the latter to be liable to be dissolved by aqueous action, or to be so affected by it as to lessen the stability. It is impracticable to