by Charles A. Gaides and Harry B. Chase, Jr.*
The land surface of the Great Woods was molded by the melting of the glacier that covered southeastern New England until about 16,500 years ago. As the glacier melted, the masses of clay, gravel, rocks and rubble carried on the ice were let down to form a blanket of "till" on the bedrock over the entire area. Floods of icy water carried enormous loads of sand and gravel, which built the terraces along the east side of the Rumford River where it flows through the northeast corner of the woods. A melt-water lake formed against the glacier front along the present Rumford River. The torrents carried chunks of ice southward until they became embedded in gravel. When the ice melted, the small "kettle holes" near Taylor's Hill were formed.
The meltwaters also gouged a half dozen parallel furrows across the Great Woods from north to south. These now show on aerial photos as long narrow swamps. The 45-acre Brier Swamp was formed when a huge isolated block of glacial ice was stranded long enough to create a depression that later filled with peat.
One feature produced by the deposition of sediments is a highly visible esker. An esker is a long, narrow, winding ridge of gravel that overlies and characteristically disregards the underlying topography. Most eskers are the in fillings of the tunnels of long sub-glacial streams, and their courses, though sinuous, are generally aligned roughly at right angles to the ice front.
The excellent example of an esker found in the Great Woods is a moderately high ridge, roughly five miles in length, and presently cut by several meandering streams. It is a most unusual sight, with its steep sides and rounded top, and seems oddly out of context with the surrounding topography.
Unfortunately for lovers of eskers, this ridge is a prime source of gravel, and thousands of cubic yards of it have been trucked away in both Mansfield and Norton.