Section 2. If buildings or fences have been erected and continued for more than twenty years, fronting upon or against a highway, town way, private way, training field, burying place, landing place, street, lane or alley, or other land appropriated for the general use or convenience of the inhabitants of the commonwealth, or of a county, city, town or parish, and from the length of time or otherwise the boundaries thereof are not known and cannot be made certain by the records or by monuments, such buildings or fences shall be taken to be the true boundaries thereof.