by John Wonnacott - Contributing Writer
In 1970, David Tobias and Dan Blankenship built a temporary earthfill cofferdam at Smith’s Cove on Oak Island, located in a position where it would isolate a section of the shore from the ocean - the place where the artificial beach, coconut fibre filtration system and finger drain system had once been said to be located.
David Tobias raised the money necessary to do the work, and he collaborated with Dan to decide on what work they would attempt to undertake in the cove.
The cofferdam was built out of glacial till, dug from the higher ground nearby. Here is the full report regarding its construction, as written by Dan Blankenship on September 18th, 1970:
"On August 13th, we started the dam around Smith's Cove. The purpose of this dam is of course to more fully explore original workings. I am very glad that this course was recommended by Ben and agreed to by David. Personally, I have felt all along that this was the logical area to explore and quite possibly prove or disprove past history. According to the record, this beach was never thourghly and systematically explored and some evidence even after these many years should still be there. After all, if any one of these five drains are encountered, when followed into the beach, should lead to the vertical shaft that would almost have had to be there in order to make the flooding effective.
The dam took 13 working days and cost $5778.72 in direct costs, which included two dozers, on front-end loader, two trucks, all common labor and bags for sand and spikes for making log coffer cribbing, which were sunk with rock in order to stabilize the deepest part. Aug. 22nd we lost the end 30 feet due to a storm and Aug. 24th we lost over 40 feet and only succeeded in saving another 100 feet by taking emergency measures which included installing a 2in. continuous plank wall 4 ft. high and about 100 ft. long to save our earth from washing away. The dam was completed August 28th.
This dam is well beyond any previous one put up by earlier searchers according to the rocks that were left. The inside top of the road measures 450ft from original shore line and the outside is much longer. the base averages 60 or more and the top is about 15 ft. wide with remaining average high tide. Approximately 12,00 yds. of earth was used in its construction."
What transpired, after the water was pumped out of the cofferdam, was that Dan Blankenship exposed a number of very interesting artifacts that were buried in the old sea bottom inside the cofferdam. One of the most interesting finds in that investigation was what has been called the “U-shaped Structure” (item #2 in the photo below).
Les MacPhie has done some great work, by keeping track of the location of many different investigations, tying them together by resolving differences in the survey systems used to locate significant items in each investigation. Following is a drawing that I received from Les, which accurately shows the U-shaped structure in relation to the finger drain system (and other notable Oak Island features) discovered by Robert Dunfield Senior, but which was mostly obliterated by the time that Dan Blankenship’s cofferdam was built.
An unusually high tide flooded Dan’s cofferdam before the Tobias and Blankenship investigation at Smith’s Cove could be completed. Subsequent tides washed out the cofferdam and the work was never repeated.
In 1970 Blankenship had observed (and recorded in photographs) that the U-shaped structure had notches sawn into it every 4 feet along the base log and also along each “arm” that pointed toward shore. Each notch had a different roman numeral cut with a hand saw beside the notch. The bottom of each notch was 6 inches wide and pointed upward and shoreward at an angle of 45 degrees. Several timbers were also found, still attached to the base log, with their upper ends rotted off, with the lower end of the timber secured into one of the notches, with a 2 inch diameter oak peg. It looked like the timbers were used to support lateral planks that would have been caulked, to form a water-tight wooden structure.
Many people have speculated that the U-shaped structure was built to serve as the inner water-tight barrier, that would have been buried inside an earthen cofferdam, to make it more permanent and more water-tight. We know that there were cofferdams built by Searchers in 1850 and again in 1866, in about the same location as the U-shaped structure; and quite possibly the U-shaped structure is partial remains of one of those searcher’s cofferdams. However the shape of the structure is a concern for me. All indications are that earthen cofferdams would be built in a smooth concave arc shape, stretching from one shore, out into the ocean as far as low tide or possibly lower, and then back to shore. Instead, the U-shaped structure has 2 asymmetrical arms that form sharp angles with the base log that runs parallel to the shore. I always ask myself: “Why would anyone build a water-tight structure in that shape – why not build it along the alignment of a cofferdam? The sharp angles between the arms and the base log are a mystery to me.
Another oddity in regards to this structure is that it does not line up with the artificial beach and the finger drain system. If the structure was part of a cofferdam, it would have been intended to either cut off the water supply to the finger drain system and flood tunnel that connects to the Money Pit - if it was built by a Searcher – or it would have been built to allow construction of the finger drains and flood tunnel if it was built by an original Depositor.
Back around the year 2000, when I was working with David Tobias and Les MacPhie, we started talking about the U-shaped structure, wondering about its real purpose, and who built it. We decided that we should go back to Smith’s Cove at low tide, dig up the shoreward end of one of the U-shaped structure arms, and recover some pieces of it so that we could do some scientific testing to determine the age of the structure.
So I used the old photograph of Dan Blankenship’s diggings, and I measured distances between large rocks to establish a scale factor, and then I went to the site where I marked out the probable location of the shoreward end of the north arm of the structure. I hired a backhoe and with the help of two laborers, we started digging an 8 foot deep trench that should intersect the structure. We set up my portable water pump to keep the excavation reasonably dry and quite miraculously we found pieces of an old log in a matter of a few minutes. At first I didn’t think we had found the structure, because everything was covered in mud. But as soon as I washed off some of the mud, I could see notches with roman numerals beside them. We recovered 3 pieces of log, backfilled the trench and tidied up the site..
After carefully washing the log pieces, I collected a clean sample of wood from one piece and sent it off for radio-carbon dating. Unfortunately the lab test came back indicating a probable age of 1860 plus or minus 30 years. I had taken the wood sample from near the center of the log, with an average of 30 tree growth rings out to the outer edge of the log, so radio-carbon dating was saying the log was cut in 1890, plus or minus 30 years. This was not very encouraging, as I was hoping that the wood was much older.
The next thing that was done, was to cut an end off one of the log pieces and send it off to a specialist in dendrochronolgy. That’s the study of tree ring growth, that allows researchers to determine the exact year that a tree stopped growing, by matching the pattern of tree rings in a log sample, to a master data base of tree rings which span a long time period. Each species of trees has a different pattern of growth, and each regional weather pattern would create a different growth pattern. So we needed to find a dendrochronological researcher who has a data base valid for Oak Island, and valid for the red spruce which was the species of log used to make the U-shaped structure. Again luck was not in our favor, and the dendrochronology researcher failed to find a match for our sample.
"...basically all radio-carbon dating results for objects less than 500 years old are unreliable."
So these two negative results discouraged me, and not much more was done on this front until 2015. However last year, when I was looking at the radio-carbon dating test results that the Lagina brothers obtained for a sample of wood they had had recently tested, I noticed two things. First, they used the same test lab that I had used 15 years ago (Beta Scientific in Miami). And secondly, the test result came back with five different age ranges. It seems that recent research into the Carbon-14 isotope concentration in the atmosphere has determined that the atmospheric C-14 concentration varied a lot in the past 500 years, and basically all radio-carbon dating results for objects less than 500 years old are unreliable.
So I decided to go back to the U-shaped structure pieces that we recovered about 15 years ago, get a new sample and have it examined by a new dendrochronological researcher who has a much bigger and more detailed set of data bases for Nova Scotia tree species. I had donated the U-shaped structure samples to Danny Hennigar, for his use as displays in his Oak Island museum in Mahone Bay. So I asked Danny to help me get a new sample from one of those log pieces. Danny supported the new research completely, we got a good sample from one of the old logs and I sent the sample off for dendrochronological testing. And that’s where we are right now – waiting for a dendrochronology researcher to see if he can get a match with the new sample. I say “we” because Les MacPhie and Danny Hennigar have supported this new research and have contributed ideas and suggestions all along the way.
It’s pretty exciting for me. If we can get a match to a date earlier than 1795, we might have the first scientific proof that the U-shaped structure was built by the original Depositors. Of course there is a bigger probability that we will just prove that the structure was built by Searchers. But if we can pin an exact date to the U-shaped structure, that will at least fill in a few blanks in the Oak Island mystery.
“Why do you think the U-shaped structure was built in the shape and location that it is?”
I would like to challenge all our readers with a question: “Why do you think the U-shaped structure was built in the shape and location that it is?” If we can learn the real purpose that the structure was built to serve, it might unlock some more answers to this part of the mystery. If the U-shaped structure was built by Depositors, it could be a vitally important question.
From The Blockhouse
is published by Blockhouse Investigations and oakislandcompendium.ca
in Nova Scotia, Canada
Editors and Chief Correspondents
Kelly W. Hancock, CD
John Wonnacott, P. Eng.
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