The first lighthouses in this country were beacons, made by piling up stones, from the summit of which "firebales of pitch and ocum" were burned in iron baskets at night. It is a far cry from that time to this, and the construction of the lighthouse of the present day is, as has already been shown, a task demanding mechanical skill and engineering ability of the first order. A lighthouse on the mainland has few difficulties involved in its construction, but where the foundation is an isolated rock, a submerged reef, or a sandy shoal, the best resources of the engineer and mechanic are called into full play. The lighthouse most difficult to build is that on the submerged rock or partly submerged rock. Race Rock Light, in Long Island Sound, belongs to this class. Portions of Race Rock are three and others thirteen feet under water. Diving-bells were used to level the foundations for the lighthouse, and the masonry and concrete under water were laid in the same way. The United States has two other lighthouses built on submerged rocks, Minot's Ledge in Boston harbor, and Spectacle Reef, on Lake Huron. The first lighthouse on Minot's Ledge was built above stout iron rods driven into the rocks. In April, 1851, there was a severe gale which lasted five days. On the third night of the storm the house was blown down and light and keeper went out together. Four years later a second structure was begun, this time with a foundation of masonry and concrete. Minot's is barely awash with the lowest tide, and so rare were the opportunities for work that three years were required to prepare the rock for the first course of stone, which was laid in 1857. In 1860 the structure was completed and has ever since stood proof against wind and storm. Spectacle Reef lighthouse, near Mackinac, was built with the aid of a coffer-dam. A large wooden cylinder was constructed by banding long staves tightly together and towed out to the rock, where it was set up on the surface and the stones driven down into the uneven places. Then the crevices were filled with cement and the water pumped out. After this the rock was leveled and the limestone courses rapidly raised one above another. Spectacle Reef light stands eleven miles from land, and its base is seven feet under water. Where there is a shifting shoal, whose unstable character no degree of mechanical or engineering skill can overcome, resort is had to the lightship. The United States has twenty-five of these vessels. Seven of them are employed off Massachusetts Bay to mark the Vineyard and Nantucket shoals, and a line of equal number lies along Long Island Sound stretching from Brenton's Reef to Sandy Hook. Four more are stationed off the New Jersey and Delaware coasts, one off Cape Charles, three off North Carolina, South Carolina and Georgia, and two off Louisiana and Texas. The life of a lightship crew, as will be told in another place, is a laborious and often a dangerous one.