Probably the most common example of poor practices in handling soil is the careless backfilling of trenches. Everyone will know examples, either in a garden or locality, of backfilled trenches which have settled, leading to hollows which clearly mark the route followed by the trench. When these cut across finsihed roads, they can often lead to serious trouble. All such trouble can be easily avoided. The usual procedure in backfilling trenches is to put back the soil either with shovels or machinery, without any reference to this state when it was excavated. The result is that the backfilled sill is not as dense as the original soil. This is usually shown by the fact that there is some excavation left over. Nature proceeds to correct the mistake that has been made, and the backfill gradually consolidates with time and under the pressures that may be applied to the surface of the trench. As the soil in the trench shrinks, it gradually becomes the hollows which are so common a feature of backfilled trenches. The whole secret of avoiding trouble in backfilling trenches is to get the soil the same density as it had before. How can this be done? In the case of sand and gravel, this result can be achieved if the material is replaced in trenches in thin layers if it is properly consolidated and vibrated as it is placed, and if it actually flooded with water when necessary. This last procedure must be carefully done since, if not enough water is used, the sand many be just dampened enough and this leads directly to bulking of the sand with subsequent settlement when it dries out.