Scattered rocks like these are evidence of Vermont's recent glacial history. Click to view a larger image.
The bedrock of South Burlington is overlain by till, a mix of rock from clay-sized particles to car-sized boulders that were bulldozed across the land at the base of the ice sheet that covered all of New England until about 15,000 years ago. This till was deposited on the terminal moraine (the edge of the glacier) when the ice sheet melted northward.
Till represents a great hazard to plows and so most farm fields were cleared of rocks before plowing. In old fields using for grazing during the sheep era in Vermont, till was collected from field and stacked as rock walls to keep livestock in. In fields were tilling would have taken place,
the farmer would have taken more care to remove smaller rocks. Stone walls along these fields contain much smaller sized till.
Till can also be easily observed along stream banks where water has cut into the soil or where fallen trees have uprooted a large chunk of the soil.