Mineshaft

Abandoned Mine Shafts are a new type of structure that was added in Beta 1.8, along with strongholds.

Structure
Abandoned mine shafts are a series of straight intersecting tunnels 3 blocks wide. They have uneven ceilings with a height of 2-3 blocks. Wooden planks make up the supports of these tunnels, but they can also be supported by fences in rare cases. Incomplete sections of minecart tracks can be found at the floor of these shafts and torches are occasionally placed on walls. Cobwebs can be found at random. Cave Spider spawners surrounded with cobweb can be found. Occasionally, stair-like tunnels can be found.

Cave Spiders are exclusive to these areas. There are chests spread throughout the mine that contain things such as gold and iron ingots, ores, food or seeds. They can even contain diamonds or pickaxes and may sometimes spawn in air as a world generation glitch. It is possible but rare to have it spawn in a ocean so the shaft is flooded. Abandoned Mine Shafts are also rich with ores such as Iron, Gold, and rarely Lapis Lazuli and/or Diamonds. As the 'shafts' are made of wooden planks, Abandoned Mine Shafts actually in turn provide very good source of wood while prospecting underground.

Obtainable items:
 * Diamond
 * Coal
 * Lapis Lazuli
 * Redstone Powder
 * Iron Ingot
 * Gold Ingot
 * Melon seeds
 * Pumpkin Seeds
 * Bread
 * Rails
 * Iron Pickaxe

Abandoned Mineshafts may be large, and may be akin to labyrinths during exploration, making it difficult to keep bearings. The poisonous Cave Spiders are very common and make exploration dangerous unless prepared. However, due to placed torches, the presence of other mobs is much lower so areas not near spider spawners are much safer than caves.

Minecart tracks may be generated floating in the air from a world generation glitch. These tracks behave similarly to floating snow in that all adjacent glitched blocks will pop out when one is mined.