NOTE.—Clean fragmentary rock of uniform size, carefully tipped, would stand permanently at any height within reasonable approach to the safe compressive load; but in deposited earth, as in cuttings, in addition to the contingency that the natural ground at the base may not be able to bear the strain, the effect of water pressure must be considered as it may become of sufficient force to cause the face of the slopes to become loose and finally separate and slip. At a height of only 50 feet clear head, the pressure would be about 22 lbs. per square inch; therefore, it is not so much the weight the deposited earth will bear as the effects of water upon the earth, and the water pressure that have to be considered. OTHER EARTHS. Description of Earth Embankment. Approximate safe permanent maximum height in feet, of an embankment in earth, conditions as described. Feet. Peat moss, marsh earth, consolidated mud, silt, 0 to 7 hard peat turf Alluvial soil obtained from a river bed 5 to 8 NOTE.—When the river bed is rocky and the deposit firm, the height may be increased to 15 feet. Soft wet pasty clay, and marsh clay, moist and 5 to 6 difficult to drain Diluvial clay soil of river beds, according to its uniform character, degree of firmness and 6 to 20 hardness Alluvial soil. Loam and loamy earth. (Clay and 40 to 70 per cent. of sand.) Clay loams (clay and 15 to 30 about 30 per cent. of sand) Damp clay soil. Equably damp, that can be drained 25 to 30 and will partly drain itself NOTE.—The earths named will generally have their bearing power increased by careful deposition in an embankment, for the act of equal separation of the mass will cause a decrease in the quantity of water contained in them: and they will be relieved of the water-pressure to which they were liable in their natural position. On the contrary, when carelessly tipped they may be deteriorated. _Vide_ Chapter IX.