Sentence:  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 <WSD>"hedgehog</WSD>", is still used in Lincolnshire. 
Meaning of the word marked with <WSD> tags:  A form of dredging machine.