THE RENSSELAER PLATEAU is filled with kettle holes formed during the last ice age. When the glacier retreats, sometimes a large piece of ice will remain unmelted on the ground. As the glacier retreats, it melts causing outwash to flood surrounding areas. The outwash may bury the remaining ice block. When that ice eventually melts, the outwash on top collapses, and a depression in the land forms, called a kettle hole. Sometimes, water will fill the depression forming a kettle pond or lake, but at the Poestenkill Community Forest, these kettle holes became marshes and bogs! Over time the kettle lakes and ponds fill with sediment and slowly turn into marshes and bogs.

Perched Pond is likely a small kettle hole. It has not developed into a marsh or bog because it dries out each summer and accumulated debris decomposes when exposed to oxygen in the air.

Little Beaver Bog and Big Beaver Bog are kettle ponds that have remained saturated with water, and the accumulated debris supports an ever-changing marsh/bog complex.