The men toiled in eight-hour shifts continuously, removing the sand within the space and sending it upwards to be discharged overboard. As the area was excavated, the cutting edge sank deeper and deeper, so that the structure became more and more firmly embedded. There was apprehension that the obstruction offered by the caisson to the movement of the currents might set up undermining around the cylinder, as in the case of the Rothersand; but the engineers arrested any tendency in this direction by dumping large pieces of stone overboard around the tub. Some 6,000 tons of stone were used for this purpose, so that the caisson has an impregnable protection. As the structure sank lower and lower, owing to the excavation, concrete was dumped around the air-tube above the floor of the space in which the men were labouring, while successive rings of iron were added to the top of the cylinder. The men worked with great gusto in their novel situation, and, the task being prosecuted uninterruptedly throughout the day and night, the cylinder sank from 12 to 24 inches during the twenty-four hours. This labour was maintained until the cutting edge of the caisson was 33 feet below the surface of the shoal, when the engineers called halt. They considered that the task had been continued to a sufficient depth to secure the requisite rigidity for their lighthouse. The men left the working chamber, which was then tightly underrammed with sand, so as to form a solid foundation, while the air-shaft was filled up with rammed sand and sealed with a thick plug of concrete. The wall of the iron cylinder had been intermittently increased in height by the addition of successive rings of plates, until the rim was 70 feet above the cutting edge and projected about 30 feet above the water at low-tide. From the bottom to a height of 40 feet it is virtually a solid mass of concrete, protected by a skin of iron 1½ inches thick. Further concrete was added, bringing the solid section to within 10 feet of the rim, so that the concrete heart is about 53 feet in height and 35 feet in diameter. It is a solid circular rock sunk into the sand, and as firm and free from vibration as a granite core. Upon this foundation a house for the light-keepers, crowned by a tower, was erected, the focal plane being 59 feet above mean high-water. It is fitted with a light of the fourth order, visible for thirteen miles. One of the most important features in connection with the Fourteen Foot Bank light was its small cost, which was below the estimate, especially when it is compared with the German work. The United States Government appropriated a sum of £35,000, or $175,000, for the undertaking, but the total expenditure was less than £25,000, or $125,000, so that a sum of £10,000, or $50,000, was handed back to the Treasury--a most unusual event in connection with Government contracts. The lighthouse was finished and brought into service in 1886.