Stone walls are an enduring testimony of the hard labors and work ethic of subsistence family farms on ~100-acre lots. Those lots had been defined by hardy teams of surveyors who used compasses and chains to define the magnetic directions and lengths of boundaries. Farmers cleared (‘improved’) large sections of their land of trees for the purpose of grazing animals and growing crops. As we venture into the deep woods today, we often encounter these forgotten stonewalls that reveal that others long ago were there. Modern airborne surveys using ‘Light Detection And Ranging’ (LiDAR) not only reveal the vast extent of these stone monuments in New York and New England (total estimated length ~200,000 miles), but also information about the slow drift of the Earth’s magnetic field.
Delano, John W. PhD, "Stone Walls of New York and New England" (2016). Atmospheric and Environmental Science Faculty Scholarship. 3.