In the article, Trow discusses how he and a team from the Minnesota State Archaeological Survey tried to determine the origin of the stones. First, they tried to test the hypothesis that these were mooring stones. As mentioned above, this hypothesis failed when the stones turned up in places boats could never have traveled and—crucially—are not found in documented Viking sites in Greenland and Newfoundland, indicating that such stones were not used anywhere else along the proposed route from Norway to Minnesota.
Next, the team tried to test another hypothesis, that the holes were the result of nineteenth century stone-blasting techniques. In that period, large stones were cleared from farm fields by drilling a small hole, filling it with blasting powder, and then exploding the stone. To make a very long investigation somewhat shorter, the team found an elderly farmer named Emil Mattson who participated in such blasting practices in the early 1900s and was able to lead the team to a failed rock blast from that era. This stone had the tell-tale drilled hole, but also had radial blast lines where the blasting powder had exploded. Unfortunately, the cleaved rock was too heavy to move, so both parts, along with the halves of the hole, remained in place. The team used the marks on the rock to identify similar markings on the foundation stones of old barns and houses to demonstrate that such buildings were constructed from rocks blasted in this way.
The mystery of the small holes in many large rocks left on the landscape can be easily explained: the ones we find today are simply those that were left unblasted, either forgotten or intentionally passed over. “They didn’t get around to blasting those,” as Mattson said. The so-called mooring stones are, in fact, recent historic artifacts, no older than the beginning of nineteenth-century farming in the region.
“Why,” Scott Wolter asks, “do the archaeologists I’ve discussed this with dismiss this thesis and insist they were made for blasting the rocks when the physical evidence refutes this?” As we’ve seen, the “physical evidence” coupled with the testimony of someone who was actually involved in chiseling these holes is rather unambiguous on this point. The reason the stones Wolter examined show no signs of blasting is because they were the ones that weren’t blasted. The existence of stones that were blasted seems to be eloquent testimony to the holes’ purpose.
That said, technically speaking, the team’s findings apply only to the handful of stones they studied, so it is theoretically possible that other mooring stones had different origins. However, given the clear and direct evidence of their origin and use, I’m comfortable generalizing that most if not all of these stones are the remains of nineteenth century land-clearing techniques.