I have been MD'ing around my home for the first time, and have a question...I recently found an area about 15 feet from the back door..at first I found an old crock pot, some broken glass, square nails etc, then about 6 inches down I hit a layer of ash and coals. Under that I found a 1934 license plate, more glass and nails, etc..well I have gone about 3 feet down, broken through 3 more layers of ash and soot, finding the same items, now I have hit a layer that looks like white chalk about an inch thick...am I onto something? Should I keep going? Why the layers of ash and coal?