This chain is laid in the bed of the river and is only fastened at the two ends.

It is seventy miles long.

It comes in over the boat's bow, passes around a drum, and is payed out astern.

She pulls on that chain, and so drags herself up the river or down it.

She has neither bow or stern, strictly speaking, for she has a long-bladed rudder on each end and she never turns around.