The first machines merely loosened, but did not raise the stuff, a scouring being afterwards effected by means of sluices. These machines consisted of large bars or prongs placed vertically in a frame, and being fastened to a barge placed in the line of the sluices, the whole was inpelled forward by the current, thereby scouring the bed. Such a machine, called a hedgehog, is still used in Lincolnshire.