» Issue 31: Spring 2002

Recovering the Oak Island treasure

Graham Harris (Civ 1958) outlines the engineering challenge

For over two centuries a small island off the coast of Nova Scotia has held a secret. The island has gained renown as the site of one of the world's last treasure hunts and, over the years, has been the scene of much fruitless endeavour to recover that which is believed to be buried there. Optimistic treasure-seekers have come from far and wide to pit their wits against the forces of nature reluctant to part with what the island holds.

The saga commenced in 1795 when a young lad, exploring the forest undergrowth, stumbled into a clearing amidst the primeval oaks. There stood a massive oak bearing a sawn off limb, from which was suspended an ancient block and tackle. Below was a depression in the ground that immediately gave rise to hope that here lay buried pirate treasure. Fuelled by such dreams, he returned the next day with friends armed with shovels. Digging feverishly they uncovered a layer oftlagstones beneath the grassy sod and then found themselves within a circular pit of about 13 feet diameter that had been infilled. Further digging revealed layers of timber logs at intervals of ten feet, obviously staging used by the originators of the shaft. Strong farm boys though they were, they had to give up their clandestine work at a depth of 30 feet.

Aerial view of Oak Island

The most secluded island

Oak Island, named from the profuse growth of timber it once supported, lies at the head of Mahone Bay, about 100 miles south of Halifax. The bay holds many islands, of which Oak Island is the most secluded. The island, no more than a kilometre long, hugs the mainland tightly and is connected to it by a short causeway. The 1795 discovery has since spawned numerous treasure-seeking ventures, and the last 200 years has seen a steady stream of individuals and consortia eager to risk both fortune and reputation. Few appear to have had any appreciation of the ground conditions that confronted them, or any inkling of what might be buried there and by whom. Some searchers have attributed the workings to Captain Kidd or the Knights Templar. Others say it was the Incas, who in some mysterious way transported huge quantities of gold northwards to elude the Spanish conquistadors. Pirate treasure featured strongly, of course, and rumour abounded that the crown jewels of Scotland and France might be buried there or possibly ancient Baconian manuscripts which, when uncovered, would usher in a new age for mankind.

There was even a theory that the workings had been dug by aliens from an unknown planet. In truth there was not one scrap of common sense reasoning, let alone any historical documentation to give credence to such fantasies. There is, however, compelling evidence to suggest that there is something buried at great depth.

A series of boreholes put down between 1967 and 1971 provide some of the most telling evidence; a number of cavities being proven from 195 to 210 feet below surface, some roofed with thick timber and iron plate. These all lie offset from the Money Pit shaft, which the youngsters first began exhuming, and is so named from the vast hoard of wealth believed to be contained therein (but equally might be named for the money that has been poured into it). Artifacts dating from the late seventeenth century, such as axes, picks and oil lamps have been recovered and, more excitingly, fragments of Ming china and traces of mercury. Although no gold, silver or jewels have yet been found, the evidence suggests that the contents of the Money Pit will prove, on recovery, to be that of a Spanish galleon. A long forgotten incident of British maritime history appears to be at the heart of this intriguing enigma.

A great deal of myth

The diggings since 1795 have shown the underground workings to consist of two main elements. These are the Money Pit shaft, which extends to 210 feet below ground surface, i.e. 175 feet below sea level; and a Flood Tunnel, that links the Money Pit to the sea some 500 feet distant. It was long assumed that these two elements of the workings were contemporary, being constructed by the first diggers on the island. Much has been made of the supposed genius who could create the cunning works that have frustrated the endeavours of all treasure-seekers since. Writers, with little or no technical background, have marvelled on such mysteries as charcoal being found upon timber platforms within the Money Pit, or within the cavities probed by the drilling. All in all a great deal of myth has developed about Oak Island.

Some years ago the writer was reading one of the many books written about the island when his attention was arrested by certain facts contained within the text. A clue, hitherto undetected by others, strongly suggested that the bottom of the Money Pit might have experienced what in mining parlance is called a 'blow-out'. Such an event takes place in a catastrophic manner when rock stresses or external hydrostatic pressure, in the vicinity of an underground excavation, exceed the rock strength. An implosion ensues. Though relatively infrequent the phenomenon is well documented, and is one that has taken many lives in the past.

Could such an event have led to the loss of treasure hidden below ground? If this was so, it would explain the construction of the Flood Tunnel, after all attempts to recover the treasure had failed. There is much to suggest this scenario as the Money Pit and the Flood Tunnel are as dissimilar as chalk and cheese. Decades could have elapsed between the excavation of the Money Pit, possibly by a ship's crew, and the highly sophisticated engineering necessary for the Flood Tunnel. Technical and historical research was to confirm this to be the case.

A feat of engineering

Despite its great depth, the Money Pit shaft penetrates easily - excavatable glacial till, and could have been dug in a matter of four to five months with a minimum of shoring and support work. On the other hand, the Flood Tunnel, which has internal dimensions of 2ft feet wide by 4 feet high (once standard in the tin mines of Cornwall and elsewhere), is a feat of engineering. It incorporates at the entrance of its seaward terminus an intricate filter system following the now universally established principles of inverted filter design. It possesses grades which would have necessitated accurate survey control during excavation, and was filled with rounded boulders for tunnel support commensurate with rapid transmission of floodwater. The tunnel and its appurtenant works are estimated as requiring no less than 18 months of construction by men equipped with all the tools, materials and gear for a full-scale mining operation. The historical evidence suggests that this was a government sponsored venture, and that the British government provided the sponsorship.

Since the intersection of the Flood Tunnel and the Money Pit occurs at the approximate mid-point of the shaft, i.e. 105 feet below ground surface, there is good reason to believe this is marginally above the level to which debris would have risen following the postulated blow-out, or was the safe level at which water could be maintained by pumping during tunnel excavation.

Years of frustrated effort

The historical record of all past treasure-seeking endeavours was gleaned in the search for hard, reliable, factual evidence that could throw light on the technical factors that have led to two hundred years of frustrated effort. The result has been Oak Island and its Lost Treasure, written in collaboration with Les MacPhie of Montreal (not an IC man!). This account is the first to be compiled on the so-called 'mystery' of Oak Island from a technical standpoint. Nothing was discovered during the course of this research that could not be explained under the harsh spotlight of science. There is now a far better understanding of the geology of the island and the various factors that have hindered treasure recovery. Having been able to establish a time frame within which Money Pit and Flood Tunnel were constructed, it is possible to present a plausible theory as to 'who' buried 'what', 'when' and 'why'. The tale that emerges is the very stuff out of which the finest historical romances are created, as it sheds new light upon one of the most fascinating periods of British history, namely the revolution of 1688 against King James. This small island, far across the wastes of the North Atlantic, appears to have played a hitherto unrecognised role in this drama.

It is impossible in an article of this length to recount all the technical and historical evidence that led to these exciting conclusions. It is only possible to deal in some brevity with the more salient features that resulted from exhaustive probings.

Geologically the island is a drumlin. Composed almost entirely of dense glacial till, it is a remnant of the last Ice Age. This till overlies anhydrite bedrock, with which is associated some minor limestone. Anhydrite possesses the dubious property of being exceedingly soluble, more so in salt water than in fresh. Paradoxically Oak Island is the only island in the region to be underlain by anhydrite. On the adjacent mainland, and on other islands in the region, sounder limestones and slates can be found at shallow depth. It was ironic that those depositors, eager to cache their hoard, selected the only island in the area that possessed a geology that would ultimately lead to its loss. At any other location they would have buried their treasure and, assuredly, safely recovered it. We would be none the wiser today, except perhaps to scratch our heads wondering who dug such a deep hole in the ground!

The Money Pit

A vicious circle

It does not take a rocket scientist, if the phrase will be excused, to appreciate that digging the first shaft through dense till into the underlying anhydrite is a simple operation fraught with little peril. But once the excavation fills up with water, drawn into it through systemic seepage paths within the anhydrite, these seepage paths will enlarge progressively. The greater the pumping activity the greater the rate of solution of the anhydrite and, of course, the greater the rate of inflow. Once started it is a vicious circle, and one likely to prove catastrophic as the solution passages enlarge. Those who returned to recover the treasure would have been unaware of these technical factors.

It cannot be determined at which point during the recovery process trouble ensued which might have resulted in the blow-out, bringing the recovery operation to an abrupt end. Amounts of coconut fibre detected at depth suggest this was used to help stem the ingress of water. Perhaps the shaft was dewatered, perhaps some of the treasure so painstakingly cached was recovered. In truth we don't know. But what is certain is that the vast bulk of the treasure was left underground, simply because a decision was made to construct a Flood Tunnel, the obvious object of which was to ensure that the treasure remained buried for posterity.

Treasure-seekers centuries later would repeatedly attempt to dewater the workings by pumping -an exercise as fruitless as trying to pump the Atlantic Ocean dry! In recent years, massive sinkholes have developed offshore showing that the seepage paths radiating outwards from the base of the Money Pit have grown great indeed. Some skilled and cunning engineering is required to combat this legacy of past malpractice, which only now has been finally understood.

Three clues are available to determine the overall timeframe of the workings:

(1) In the 1930s, excavation within the Money Pit shaft penetrated deep enough to encounter what is believed might be debris material resulting from the blow-out. Several artifacts were recovered, the most important being an old axe. Archaeologists ascertained that the axe was of a type that was used about 1680. This is the earliest reliable date that can be affixed to the workings with any certainty. The application of radiocarbon dating to oak fragments has proved less certain, mainly due to the longevity of such trees and the lack of knowledge regarding what part of the tree any wood might have originated from.

(2) The reports of charcoal having been found on the platform of logs at a depth of 30 feet within the Money Pit suggest that charcoal furnaces were used to provide ventilation during the excavation of the Flood Tunnel. In the seventeenth century, furnaces were used to induce convection currents in underground workings. This practice was first described by Sir Robert Moray in 1665 in a paper delivered to the Royal Society, after which the practice was widely adopted. By the use of furnaces in shafts and tunnels, foul air was sucked through the furnace and burned, and replaced by clean air sweeping through the workings.

(3) The first land grant in the area awarded by the British colonial administration was in 1759, and included the following interesting phrase relating to mineral rights:

The said township is to consist with all and all manner of mines unopened excepting mines of gold and silvel; precious stones and lapis lazuli.

The credulous might be excused for 'believing this applies to gold, silver and precious stones in their natural state. However, only the gullible would suppose it to apply to lapis lazuli, a highly treasured gemstone originating in Central Asia, and which featured in trade between China and Spain, via central America, in the seventeenth century. The inference that can be drawn is that the phrase relates to treasure that the British government knew was buried in the region but was unable to recover.

On the basis of all technical and historical factors that could be gathered from these considerations, the conclusion was drawn that the original Money Pit shaft was excavated in the l680s, while the Flood Tunnel was dug some half century later - the overall time span being from about 1680 to 1759.

In 1687 William Phips of Boston successfully located the wreck of a Spanish galleon off the coast of Hispaniola. He was the son of an itinerant gunsmith from Bristol who had settled in what is now Maine. Phips was brought up in the backwoods with little tutoring, and to the end of his life remained scarcely literate. Despite this lack of learning, he was bold, audacious, capable of building his own ships, and a master mariner. His finding of this wreck, which had foundered on its homeward voyage in 1641, is told in fascinating manner by Peter Earle in his The Treasure of the Concepcion. The Concepcion broke apart upon a coral reef that rose up fifty feet from the ocean bed. Driven by the howling gale and beginning to sink at the head after the bow struck, the stricken vessel was slammed side on to the reef and, after parting amidships, the stern section was carried over the reef. Phips discovered the bow section and in a few months at the wreck site his crew managed to haul some 28 tons of silver from the deep. The log-book entry for one day reads:

Our boats went to work on ye wreck and in ye evening brought on board 2,399 pounds weight of coyned silver

For this remarkable enterprise, Phips was knighted by King James. He was the first colonial from British North America to be so honoured.

A return expedition

Immediately a return expedition was mounted to seek further booty. From all accounts Phips was reluctant to return to the site, which is strange as one would have expected him to have been eager to lead an official party back to the scene of his greatest achievement. During this second visit, an unusual incident occurred which has puzzled and perplexed historians. While the flotilla was at the wreck, Lord Mordaunt, 3rd Earl of Peterborough, appeared with five Dutch men o' war. Mordaunt was at odds with King James since his accession, and was constantly urging William, Prince of Orange, to attack England.

It has been suggested that his visit was an attempt to wean the various captains, including the highly respected Sir John Narbrough, to transfer their allegiance to William in the impending revolution. Since the navy, as a body, was to rise up against James at the outbreak, it is virtually certain that all those at the wreck were already partisan to William, except perhaps Phips. The latter might have been conscience-stricken in associating with those antagonistic to the king who had honoured him with a knighthood. Lord Mordaunt remained in the vicinity of the wreck for the entire duration of the recovery operations. In view of the prevailing politics it is not surprising that little treasure accompanied the flotilla on its return to England. The only ship not to return was that captained by Phips, who sailed alone to New England in his 400 ton merchantman.

Entombed in coral

The lack of treasure was explained in several ways. One was that the coral had entombed the wreck, and that it was so hard and so thick that it was impenetrable. This might have satisfied King James and Samuel Pepys, to whom all logbooks had to be sent for scrutiny when naval vessels returned to England. However, coral does not grow either fast enough, or so hard, in a mere forty years to prevent earnest divers from penetrating a vast hoard of riches, especially as 28 tons of silver had been recovered from the bow section on the first visit. The Concepcion also carried chests of emeralds, pearls, plate, bullion, Chinese trade goods, including Ming china, and, of course, lapis lazuli.

Since the Phips-Narbrough expedition of 1687-88, the wreck site has been revisited on a number of occasions, including some in the twentieth century using advanced technology. No significant treasure has ever been found -a few pieces of eight, a gold chain, a ring or two, nothing more. Where has all the treasure gone? The evidence points to the Money Pit on Oak Island.

The historical record shows that Phips sailed alone from the wreck site bound for the shores of New England. It also reveals that Mordaunt's Dutch men 0' war departed the same day. The inference is that Mordaunt was there to protect Phips' treasure-laden vessel, bound for its undisclosed location on the rocky shore of what is now Nova Scotia. The revolution in England took place soon afterwards, possibly catalysed as much by the immense riches about to fall into William's grasp as by the politics of the day. Mordaunt was to rise in power and position immediately after the revolution, and Phips is known to have bragged that his financial future was assured. Mordaunt, however, soon fell from grace and Phips fared little better, when William eventually heard of the loss of the treasure.

Many have tackled the uncertainties of Oak Island in the past. Most have been adventurers and speculators, but included among this number have been representatives of such distinguished bodies as the Smithsonian and Woods Hole. Even Franklin Roosevelt, before he became president of the United States, was a participant. Perhaps it is time that an element of trans-Atlantic rivalry was introduced. After all it was the English that recovered the treasure from the watery depths off Hispaniola, and it was the English from which it was taken by a vagary of nature. It would be appropriate if British engineering was to playa role in its recovery.

Some unique engineering challenges have to be faced by the next generation of treasure-seekers. This could be one of the most exciting developments in the application of advanced geotechnical engineering, and for a most unusual purpose: It would illuminate a long-forgotten incident of British maritime history and show that engineering has a role to play in unravelling some of the mysteries of the past. Perhaps one day, the Imperial College Engineer will herald such a triumph.


(1) Earle, Peter, The Treasure of the Concepcion: The Wreck of the Almiranta. New York: The Viking Press, 1980

(2) Harris, Graham and MacPhie, Les: Oak Island and its Lost Treasure. Halifax, Nova Scotia: Forrnac Publishing, 1999

(3) Moray, Sir Robert, An Account how Adits & Mines are Wrought at Liege without Air Shafts. Philosophical Transactions of the Royal Society of London, Volume 1, No 5, July 3, 1665

Graham Harris took Civil Engineering at Imperial College (1958-61 and 1962-63), then specialised in practical soil mechanics applied to large projects mostly in the mining industry. These projects were widely scattered, but mainly in North America and Africa. Involvement in potash plant construction in the Dead Sea presented the opportunity for innovative research into the Biblical saga of the destruction of Sodom and Gomorrah. This led to a paper which was used by the BBC as a basis for one of their episodes in the Ancient Apocalypses series. Oak Island has proved an equally exciting geotechnical challenge, the book having attracted much local interest. This has prompted various studies into the history ofpiracy, and the tantalising mystery of what happened to Captain Kidd:Streasure. This research is being compiled into Treasure and Intrigue: The Legacy of Captain Kidd, which will be published later this year.

Some copies of Oak Island and its Lost Treasure are available from CGCA, priced 12.50 (inclusive of p&p in the UK), with proceeds to the Old Centralians Trust. Contact CGCA to check availability. Copies can also be purchased from Avonlea Books, 240 Water Street, Summerside, PEl, CIN IB3, Canada at C$20 plus p&p. Tel/fax: (902) 888-2665, Email: Visa accepted.

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