In 2009, at a workshop on biochar at the Pony Farm in Temple, NH, Hugh McLaughlin gave some history and ideas about the actual formation of the Black Earth. First, most of it was not black. There was Terra Mulata, brown earth.
Hugh McLaughlin, PhD, PE has a professional consulting practice in Chemical Engineering. He is an expert on the properties and production of chars, created by pyrolyzing biomass, and the subsequent conversion to activated carbons.
The Tri-State area where New York, Massachusetts, and Connecticut border each other was the home of military ironworks for the Revolution, the Civil War, etc. The forests were stripped of trees for charcoal needed to produce iron. Quite a few iron furnaces have been reconstructed, but of the charcoal kilns these are the only ones I know of, reconstructed and left in nature in the hopes that they will be respected. In fact, I have mixed feelings about putting them up on the Internet and, as you might have noticed, I have been cagey about where they are located.