Minecraft wiki entry for Cobblestone_farming, associated text: Pistons can be used to automate cobblestone generation and reduce the amount of cobblestone lost. Piston cobblestone generators work on the same principle as standard generators, but rather than mining, a piston pushes the fresh stone out of the way, allowing the streams to touch once again. Piston cobblestone generators can be used both to create a large supply of cobblestone that the player can mine later, or to supply a self-repairing structure with blocks. The piston can be driven by a clock, or by a circuit to detect when a cobblestone block has appeared. The cobblestone will extend in a long line or pillar; if you don't want it to extend out to the full 12 blocks, you can "cap" it with any unpushable block. Furnaces will do fine, and you have plenty of cobblestone handy to make them.