East shore of Lake Michigan.
Little Sable Lighthouse, a white brick tower, 107 feet in height, connected to the keeper’s dwelling, and surrounded by a picturesque group of trees, stands on a point about 10 miles south of Pentwater. The lighthouse was built in 1874, and the light now shown from the tower is fixed and flashing white, the flashes being of 40,000 candlepower. Several miles to the northward is Big Sable Lighthouse, on the point of that name, distinguished at night from Little Sable by having a fixed white light, and by day by the color of the tower, banded in black and white. Big Sable Lighthouse is the same height as the tower at Little Sable, but was erected in 1867. [(1)] [(2)]
MICHIGAN
SPECTACLE REEF LIGHTHOUSE, LAKE HURON
The Spectacle Reef Lighthouse cost $406,000 and is the best specimen of monolithic stone masonry in the United States. The work on the lighthouse, which stands on a submerged limestone reef off the eastern end of the Straits of Mackinaw, was commenced in May 1870. It was planned and built by Maj. O. M. Poe, who was General Sherman’s chief engineer on his march to the sea. The light was first exhibited from the finished structure in June 1874. The available working time on the structure was, however, only about 20 months, because no work could be done on it during the winter months.
The nearest land to Spectacle Reef is Bois Blanc Island, 10½ miles away. The stone for it was prepared at Scammon’s Harbor, 16 miles distant and one of the items in its cost was the purchase of a steamer to convey the materials to the site.
The waves at Spectacle Reef have a fetch of 170 miles to the southeastward and the ice fields, which are moved by a current and are thousands of acres in area, are often 2 feet thick. These had to be especially provided for because when they move in mass, they have an almost irresistible force. This force was overcome by interposing a structure against which the ice is crushed and by which its motion is so impeded that it grounds on the 7-foot shoal, which thereby forms a barrier against other ice fields.
The tower, in the shape of a frustrum of a cone, is 32 feet in diameter at the base and rises 93 feet above the base, which is 11 feet below the water. The focal plane is 4 feet 3 inches above the top of the parapet, making it 97 feet 3 inches above the top of the submerged rock and 86 feet 3 inches above the surface of the water. For 34 feet up the tower is solid and from them on up it is hollow. In it are five rooms, one above the other each 14 feet in diameter, with varying heights. The walls of the hollow portion are 5 feet 6 inches at the bottom, tapering to 16 inches at the spring of the cornice.
The blocks of stone below the cornice are 2 feet thick, and those of the solid portion of the tower are cut to form a lock on each other in each course, and the courses are fastened together with wrought iron bolts 2½ inches thick and 2 feet long. The tower is bolted to the foundation rock with bolts 3 feet long which enter the bed rock 21 inches, the other courses receiving the bolts for 9 inches. Each bolt is wedged at both ends, and the bolt holes, which were made with a diamond drill, after the stones were in place, are plugged with pure portland cement, now as hard as the stone itself. Hence the tower is, in effect, a monolith.
The stones were cut at the depot at Scammon’s Harbor, 16 miles away, and fitted, course by course, on a platform of masonry. The stones were so well prepared that a course could be set, drilled, and bolted in 3 days.