Feature Marked in blue is what appears to a segment of stone wall. This feature passes through a fissure or split in a boulder or exposed bedrock. Split boulders and fissure in bedrock were utilized, linked to, or otherwise factored into a number of Native American stonework sites in New England. There is a growing consensus that these splits or fissures were considered “spirit portals” to the Underworld.
James Gage http://www.stonestructures.org/