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The whole derrick is set up by keys, no mortices or tenons being used, and thus the complete rig may be readily taken down and set up on a new site.
On their level tops the beams supporting the platforms were laid and fastened by wooden pins, or inserted in mortices cut in the heads of the piles.
The case is almost complete, and empty mortices and slots show the precise positions of a few missing back and side panels.
The crests have wood spigots which are mounted in slots or mortices in the cornice frame.