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Synensys t1_j7fy7ne wrote

Reply to comment by ThisOriginalSource in Lead Plates and Land Claims in North America and Europe: When did the practice begin of burying lead plates to establish ownership of land, and why did it die out, and was it ever used successfully in a court of law to establish ownership? by whyenn

The basic idea is that magnetic north moves around over time (magnetic north and the north pole are not the same location). So if your boundary line is defined as a north south line, and you look at a compass to figure out where to put your wall, over time the direction that wall points relative to older walls, will change.

So present day scientists can use the orientation of the walls to track changes in the location of magnetic north pole.

https://theconversation.com/old-stone-walls-record-the-changing-location-of-magnetic-north-112827

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