I dug through the charcoal layer in one with my hand and started pulling up orange clay. I intend to dig in a barrel hole or two and see if I can find any tar left in the soil.The charcoal had a faint pine smell after all these years,wonder if tar will as well?I learned something in that one Al. I was puzzled as to why the tar would not simply lay on the ground in the pit and not move to the center. Now I realize the base is sloped towards the center, and the ground beaten hard with a clay covering. That prevents the tar from soaking in and just lying there.