The material of which the tower is built is the fissile flag of the island. The stones are flat, sometimes as much as 2 feet in thickness, but mostly much less, and they rather diminish in size towards the top of the tower. The stones bear no mark of a tool, and the masonry is not coursed, but compactly fitted together. The wall goes up with a curve like that of a lighthouse, and its external appearance (Fig. 160) is suggestive of great solidity and strength. This suggestion of solidity, which is due to the bulk of the building rather than to the character of its masonry, is further intensified by the absence of external openings, the whole exterior surface being unbroken by a single aperture except the doorway. It is on the level of the ground on the S.W. side, and is about 5 feet 3 inches high by 2 feet 11 inches wide, passing straight through the thickness of the wall, but widening considerably at a distance of about 7 feet from the outside and rising in the roof. Entering by this tunnel-like passage through a wall 15 feet 6 inches thick, the visitor finds himself in the interior of a circular well-like court, open to the sky above, but completely surrounded by a wall of that thickness and 45 feet in height. From the inner circumference of this court (as seen in the ground plan, Fig. 161) there open at various places other doorways leading into oval chambers constructed in the thickness of the wall nearly on the ground level. These chambers are three in number. One placed to right of the entrance is 16 feet in length, 5 feet 9 inches wide, and 9 feet 9 inches high. Its doorway is small, 3 feet high and 2 feet wide, passing through 4 feet of the thickness of the wall. A second chamber opposite the main entrance is 14 feet long, 6 feet 10 inches wide, and 10 feet 6 inches high. Its doorway is also small, 3 feet 4 inches high and 2 feet 9 inches wide, passing through a thickness of 4½ feet of walling. The third chamber, situated to the left of the main entrance, is 14 feet long, 5 feet 6 inches wide, and 9 feet 6 inches high. Its doorway is 3 feet 2 inches high and 2 feet 3 inches wide, passing through 4 feet of walling. All these chambers are irregularly oval in form on the ground plan. They are roofed in a peculiar manner. At variable distances from the floor the walls begin to be brought inwards by projecting each stone slightly beyond the face of the stone below it. In this way the distance between the opposite walls is gradually lessened as they rise in height until they come near enough to admit of single stones being laid across the space between wall and wall. This style of converging the walls inwards to obtain support for a roof of single stones is not new to us. We have met with it in the beehive houses of the early Christian monasteries and in the inverted boat-shaped roofs of their churches, built of uncemented stones on a rectangular ground-plan. It is the style of roof which is common to all