Bags of rocks are the weapons in the first world of Cadaver. The point is to walk around, figure out what the puzzles are and try to solve them. The game is quite unforgiving, it does not hold your hand anywhere. You are thrown literally and figuratively into the deep and you have to figure everything out yourself, with a cryptic hint here and there in books and scrolls.
edit: of course TCD the master spammer is first.