In June 1892 excavations were begun for the construction of an effluent culvert from the Twickenham Sewage Works to the River Thames. The work was commenced at the foreshore of the river, near the celebrated Pope's Grotto. The Thames is a tidal river at the that point, with a difference of about 8 feet between high and low water: the low-water line is 5 feet above Ordnance datum. The excavations commenced at low-water level on the Middlesex bank of the river, and were continued in a north-westerly direction, with an incline of 1 in 500, through certain roads and lands towards the Sewage Works. The length of the section was about one mile, and the width of the cutting was 4 feet 6 inches. The sloping bank between the river and the Kingston main road consisted of soft, loose materials, which had evidnetly been deposited there in modern times. After crossing under the main road, distant about 60 yards from the river, the excavation, which at this point was about 10 feet deep, entered into the reddish-yellow gravels which abound in this neighbourhood. It was then continued for some distance through these gravels under a roadway called Pope's Grove, at depth varying from 12 to 19 feet. A considerable quantity of water was found in the excavation, and had to be pumped. Beneath the gravels was the London Clay, which was met with in the excavation at two points, and in one place was penetrated to a depth of 5