nice to get down to it again ,) You dig through the rubble and create a new extension to your mine.You grab your sharp piece of stone, estimate your current depth and scribble '40' to the wall. thou this seems to be the end of the line. You attempt to make an extension to your mine, but it seems you have reached the limits of your skill. The mine wall collapses on you no matter how you try to support it. Maybe you should start over with renewed strength in another location. Minecrafting 101%.