About 15,000 years ago, a retreating glacier dropped off a big chunk of ice that created the bog's three basins, the deepest of which is forty-five feet. The basins were lined with waterproof clay. The ice melted and filled the basins. Rain and snow and runoff from surrounding areas are the bogs's only sources of water. The basin is not fed by streams and the clay liner keeps out groundwater.
Water leaves the bog only through evaporation and by plants giving off moisture.
So the bog is different from a swamp, marsh or pond. Only special plants grow in its stagnant, acidic, nutrient-poor water. Indians and early settlers used it in bandages and babies' diapers. Trapped water and liquefied peat lie under this 1-2 yard thick mat. The floating mat supports the special shrubs and trees that grow here.