The Stone Wall Initiative
Though based in Connecticut, The Stone Wall Initiative website offers much for the Maine stone wall enthusiast and preservationist—like this description of "abandoned walls."
More affectionately known as "wild walls," this type is usually fairly old; farmstead walls that have since tumbled and become unkempt. Very few of these (especially the oddest-shaped constructions) may be pre-European in age. Regardless of their original origin, all have since become ruins.
These are the woodland walls where, if a stone falls down, it's usually left where it fell. They are not taken care of. This makes them no more, and no less, wild than the creatures that live on, below, within, and near them. The fact that they are tumbled doesn't diminish their importance, because they have become part of local ecologic and watershed processes. [Link]