http://breezewiki.vernccvbvyi5qhfzyqengccj7lkove6bjot2xhh5kajhwvidqafczrad.onion/minecraft/wiki/Superflat
Each code has three main parts, divided by semicolons. They are: a list of one or more block IDs ; The block list is a comma-separated list of block IDs, ordered from layer -64 up ; if the entry for a given block has an "*", the number before the "*" is the number of layers to be generated, and the string after is the block ID.