What is "to lap timbers"

Lap \Lap\, v. t. [OE. lappen to fold (see Lap, n.); cf. also OE. wlappen, perh. another form of wrappen, E, wrap.]

1. To fold; to bend and lay over or on something; as, to lap a piece of cloth.

2. To wrap or wind around something.

   About the paper . . . I lapped several times a slender thread of very black silk.
   --Sir I. Newton.

3. To infold; to hold as in one's lap; to cherish.

   Her garment spreads, and laps him in the folds.
   --Dryden.

4. To lay or place over anything so as to partly or wholly cover it; as, to lap one shingle over another; to lay together one partly over another; as, to lap weather-boards; also, to be partly over, or by the side of (something); as, the hinder boat lapped the foremost one.

5. (Carding & Spinning) To lay together one over another, as fleeces or slivers for further working.

   To lap boards, shingles, etc., to lay one partly over another.

   To lap timbers, to unite them in such a way as to preserve the same breadth and depth throughout, as by scarfing.
   --Weale.