Under the mat a peat bed develops. The acidic water slows the decay of the sphagnum moss and other plants. With time, the peat may fill the bog from the mat to the bottom.
Beneath the mat, a layer of peat develops. Acidic water inhibits the decay of sphagnum moss and other plants in this area. As time passes, the peat can expand throughout the bog, starting at the mat and reaching the bottom.