Excavation by S Nelson and D Hartley of EEHAS. The remains of some of the buildings associated with the gunpowder mills that operated along this upper reach of the Hogsmill river during the 18th and 19th centuries, until the mills closed in c1875, were revealed. Work took place in the area of the Corning House and Mills buildings shown on the 1866 OS map. A plan of 1863 notes those furthest downstream as the Incorporating Mills. Recording concentrated on the Incorporating Mills site where works exposed stretches of brickwork in the left bank of the river. Machine excavation removed some of the brickwork but the plan of the foundations and a section through the remains were recorded. These comprised the ends of two buildings set at an angle to the river with a central channel between them and splayed outer walls extending to the river where they had been broken through by a later concrete revetment. The brickwork had been set in what appeared to be natural London Clay and were covered by a layer of demolition rubble, sealed by a layer of redeposited, silty clays resulting from recent dredging. The brickwork revealed in this area appears to relate to the pair of mill buildings and water-wheel channel shown on maps on the left hand braid of the river, where it had been split into three streams and is clearly more complex than the simple rectangular outlines shown on the 1866 OS map. A second pair of mill structures presumably still survives further over, under the right-hand bank. These buildings, together with their holding ponds and ancillary buildings, serviced two pairs of grinding wheels in the Incorporating Mill. (Bulletin 441)