This shows some of the wet grinding pans used for grind bone or China stone/flint. Two of these are constructed from wooden staves while the one on the extreme left is constructed from metal. The griniding is performed by pushing chert runner stones over a bed of chert. The pan furthest from the photographer shows a vertical shaft extended upwards to drive the sack hoist for hauling raw material up from the lower floor.
SJ8746 : Stoke Top Lock I believe the cover was over a maintenance dry dock that also had a barge weighing mechanism in it. Further corroboration would be welcome.