1850 Cofferdam remains

About This Structure

Remnants of a searcher-built cofferdam at Smith's Cove were found by the 1909 Bowdoin expedition. At least three cofferdams were built across the cove by treasure hunters to hold back the sea from the flood system's filter bed: an earth dam by the Truro Company in 1850, which was breached by unusually high tides; a wood and clay dam by the Halifax Company in 1866; and an earth dam by Triton Alliance in 1970. S.C. Fraser, the Halifax Company's foreman, reported that the 1866 dam was twelve feet high, 375 feet long, and extended 120 feet offshore from the high-water mark. It worked for a period after the cove was pumped dry but was destroyed by the sea before the area could be fully explored.

In January 2004 John Wonnacott recovered timbers from the area of the old cofferdam and submitted them for dendrochronology and carbon dating. According to Graham Harris and Les MacPhie, the geotechnical engineers who wrote Oak Island and its Lost Treasure, the tree-ring count did not settle the date, but the carbon dating results were consistent with the period of the Halifax Company's work in 1866.

Dan Blankenship's 1969-1970 excavations inside the cofferdam area revealed older wooden structures beneath and alongside the searcher cofferdams. The Geochron Laboratories dating of an oak peg from a timber structure in this area returned 1090 ±140 BP (about 860 AD, range 720-1000), and an inclined beam returned 815 ±110 BP (about 1135 AD, range 1025-1245). Taken at face value, these dates suggest the searcher cofferdams were built over or near structures of considerably greater antiquity. Harris and MacPhie offer an alternative reading of the largest of those structures, the U-shaped log structure. Its exposed length was about 155 feet; extended to the high-water mark at both ends by earth fill, the total would come very close to the 375 feet Fraser reported, and its outer section lay about nine feet below present high water at spring tide, consistent with a twelve-foot dam. They therefore allow that the log structure could be part of the Halifax Company's 1866 cofferdam, while also setting out the case that it belongs to an original construction cofferdam of the eighteenth century.

Blankenship's September 1970 report also describes the remains of a stone-paved road from the cofferdam area toward the Money Pit, a large horseshoe-shaped stone and cement foundation approximately 150 feet south of Smith's Cove beach (roughly 12 feet wide, 25 feet long, 3 feet deep with cemented stones), and evidence of extensive heat and burning along the shore with charcoal and coal deposits. He speculated this could be the site of a steam boiler used by searchers, or alternatively an original hearth furnace for metalwork.