from The Century Dictionary.
- noun A log which, caught by a rock or other obstruction in a stream, causes a jam of logs.
Sorry, no etymologies found.
The key-piece A is now put in position, and the puzzle is completed.
The "key-piece" of the jam was fully exposed, and once it was cut in two it would no longer hold the accumulation of logs together.
One log after another was detached from the disordered mass and sent whirling off down stream, until at the end of an hour's arduous exertion, the key-piece -- that is, the log that had caused all the trouble -- was found.
A few more moments would tell; for his axe was dealing tremendous strokes, before which the key-piece, stout though it was, must soon yield.
The foreman throws aside his axe and prepares to jump for life; and, like one man, the breathless onlookers shout together as the key-piece rends in two, and the huge jam, suddenly released, bursts away from the rock and charges tumultuously down the river.