What happened to the rock and dirt Twain tossed out of the mine shaft with his shovel?

From the text:

I went down with a long-handled shovel (the most awkward invention yet contrived by man) to throw it out. You must brace the shovel forward with the side of your knee till it is full, and then, with a skilful toss, throw it backward over your left shoulder. I made the toss, and landed the mess just on the edge of the shaft and it all came back on my head and down the back of my neck. I never said a word, but climbed out and walked home. I inwardly resolved that I would starve before I would make a target of myself and shoot rubbish at it with a long-handled shovel.