Another Philadelphia client is responsible for this shingled whimsy. It is sited low, close to the water on a cove, and semi-embowered, embraced by a boatyard. It is uncompromisingly round, 45 feet in diameter, as its successive names suggest. It makes mock reference to the round, multitowered ruin of Fort Dumpling, which still existed atop its nearby dumpling into the 1890s.

A close look at the profile of this “cylinder” reveals the typical surface plasticity which is among the subtler qualities of the Shingle Style and is rarely encountered in its twentieth-century revival. Its profile is subtly modulated. An outward batter establishes a base from the ground halfway up the curved wall to the second story. Then a straight-up cylinder rises through the second story. Above these windows a swell expands to a slightly larger cylinder through the third-story windows. An inset wooden molding running along their tops provides the base for the culminating swell of the cornice in two segments: below, a transitional shingled band, before another inset molding underscores the broad, shingled parapet which caps the cylinder as (returning to the metaphor) a “bastion” rim. Newhall playfully mixed the metaphor by taking his fort to sea in naming it after the famous Civil War ironclad. But the plastic response of the curved and shingled surfaces of Jamestown's windmill may also have inspired this inverted, bowl-like variant. The scattered effect of its widely separated, paired casement windows also suggests the comparable effect of the placement of openings in ancient windmills. Look again, however, and note the symmetry with which the apparent scatter is organized around the climactic arc of casement window at the top floor immediately under the bastion.

The three-story round house nudges a rock ledge, which penetrates it as an exposed interior feature. A stair climbs to a bridge crossing the ledge, which expands to a deck off the cylinder toward the sea. (In 1901 a smaller three-story house of a conventional nature was added adjacent to the stair to house a cook and other servants. A fire of 1991, which seriously damaged the main house, completely demolished this adjunct.) The drawbridge/gangplank brought visitors directly into the living hall (or “saloon,” as Newhall, with his penchant for the nautical, chose to call it) at the core of the cylinder. A cobblestone fireplace laid up against the intruding ledge dominated the saloon. “Staterooms” surrounded it, with stairs to more above. At ground level were the “galley” and storage rooms.

Did the distinguished McKim design it? A contemporary newspaper article says so, and architectural qualities reinforce the possibility. As a Philadelphian, he could have known Newhall personally. McKim, then in the midst of discovering colonial architecture, would have delighted in the opportunity to bend classical and American forms to such playful purpose. The surrounding Clark Shipyard, whose owners occupy the house, was founded about 1935 by Earl C. Clark, who previously captained and maintained Newhall's yachts.