once located little or no movement takes place afterwards. But when piers are to be sunk by the pneumatic process or by open dredging, great care must be taken at every step, because the pier is always either moving or liable to move at any moment. In sinking piers by either of the two last-mentioned processes, the resident engineer should keep such notes that from them he can report daily as to the exact horizontal position of the cutting edge of the caisson, the position of the top of the pier, the elevation of the cutting edge, the inclination of the axis of the pier to the vertical, and the amount, if any, that the pier has been revolved around its vertical axis. The Contractor can conduct his operations with much more certainty of landing the pier in its true position, if he be kept informed as to its relative position every day.

If temporary staging be used around the pier, from which to conduct the operations of construction, keeping track of the various motions of the pier will be a comparatively easy task, for the approximate alignment can be obtained from temporary points located on the staging, which points, however, need occasional checking to see that the staging has not shifted slightly.

If there be no staging, all locations will have to be made by triangulation, and, as before stated, two points on each pier will be needed in order to detect rotation. When the caisson has reached a considerable depth, however, the liability to rotate is greatly lessened.

After all that may be said, the work of keeping the pier in correct position will be dependent on local conditions and many varying requirements.

In respect to the levels, care should always be taken to preserve such measurements as will enable the leveller to keep a record of the vertical distance from the cutting edge to the top of the crib at each of the four corners. This will be necessary in order to determine how much the said cutting edge is out of level.

In giving the final elevations for the copings of the piers, it will sometimes be found necessary to take very long fore-