Important questions to determine when a slip has occurred are:— 1. Should the whole or part of the earth that has slipped be removed? 2. How are the voids to be filled that have been caused by the slip? 3. Can the disturbed material be again used? 4. What protective measures should be adopted? A thorough examination of the site of a slip and the slipped earth is absolutely necessary before the most effectual and economical means of restoration can be determined, for weakness or the presence of a disturbing agent in the upper or lower portion of a cutting or embankment may be the cause of movement. An embankment may be solid in the mass and only portions may slip and subside, but then may become unstable and require different treatment, or local restoration may alone be necessary, and the slipped earth to be removed be small in quantity. Extensive slips of the whole of an embankment usually occur from springs in its seat or the existence of a flow of water upon the ground under the base, producing a greasy surface. Should it happen that an embankment of pervious soil is tipped upon impervious ground having a depression resembling a basin, water will accumulate until it reaches the level of discharge, and a serious slip may result. In such a case the slipped earth must be removed and the water tapped and permanently drained. The upper portion of an embankment may slip and the lower be stable; if so, it is not so serious as when movement commences at the toe and the slope bulges outwards and the embankment subsides; in the former case, provided the lower portion is not affected or its drainage obstructed, it may not be necessary to remove the slipped earth, but it is advisable to drain it, and any localization or lodgment of water between the slipped mass and the firm part of an embankment must be prevented, or the toe of the slope will be made in an unstable condition. In cuttings in order to keep open the formation the whole of the slipped earth may have to be excavated, but in embankments, so long as the soil does not extend outside the fencing, its entire removal becomes optional, and is unnecessary provided further movement be prevented, and the soil drained; but in most treacherous earths, although a slip may be arrested, it will generally be a place requiring constant watching, and be one of doubtful stability. Earthwork slips require to be remedied as soon as possible after they occur, not only to repair them and obviate an interruption of traffic, but in order that the unslipped portions may not be deleteriously affected and movement be induced.