After ascertaining by experiment the pressure any earth will bear over a given area, the object should be to make the soil neither drier nor wetter than that of its natural state when experimenting, and it should be maintained in that condition. In testing the weight which a soft earth will support, some days should be allowed for the sinking of the test platform, and such subsidence should be ascertained periodically by careful levels. A month is not too long for a reliable and complete test, as many soft soils continue to yield. In soft clay soils considerable depression often proceeds for weeks after a load has been applied, but except in peculiar earths such settlement will ultimately be imperceptible, and will practically cease. A considerable margin of stability should in all cases be allowed. Although it may not be absolutely necessary to experiment when the nature of the ground is well known, wherever stability is of great importance, the cost of a practical experiment being so small, there is no sufficient reason why an actual test of the sustaining power of the soil should not be made in the majority of instances, for there are many earths whose friction and cohesiveness can alone be depended upon for resistance to displacement. In such cases the initial pressure upon the earth should not be much exceeded. Description of Earth. Approximate Safe Maximum Load in Tons per Square Foot. Bog, morass, quicksand, peat moss, marsh-land, silt 0 to 0·20 Slake and mud, hard peat turf 0 to 0·25 Soft wet pasty or muddy clay, and marsh clay 0·25 to 0·33 Alluvial deposits of moderate depths in river beds, &c. 0·20 to 0·35 NOTE.—When the river bed is rocky and the deposit firm they may safely support 0·75 ton, but not more. Diluvial clay beds of rivers 0·35 to 1·00 Alluvial earth, loams and loamy soil (clay and 40 to 70 per cent. of sand), and clay loams (clay and about 30 0·75 to 1·50 per cent. of sand) Damp clay 1·50 to 2·00 Loose sand in shifting river bed, the safe load increasing 2·50 to 3·00 with depth Upheaved and intermixed beds of different sound clays 3·00 Silty sand of uniform and firm character in a river bed 3·50 to 4·00 secure from scour, and at depths below 25 feet Solid clay mixed with very fine sand 4·00