Gettin' Down to the Nitty-Gritty

Last Tuesday, we visited our site to analyze the ground beneath it, from the bedrock to the organic layer. Although there are no bedrock outcroppings on our site and we didn't dig deep enough to find it, geologic maps of Vermont show that our site stands on the Monkton Quartzite formation. Quartzite is a metamorphic rock formed when sandstone (a product of sand and feldspar, the two most common minerals found on Earth) is subjected to intense pressure and heat as it is subducted under other layers of rock (Frank). This indicates that the rock under our site was near the shore of a shallow ocean or lake at some point in its history, which corroborates theories indicating that all of Vermont was once underneath the Iapetus Ocean.

More recently, when the geology and landscape of New England looked more as it does today, glaciers covered most of the region, and as these glaciers melted, they formed a freshwater body known as Lake Vermont, which covered most of the state. Our site was probably again on the edge or in a delta of this body of water, where the sand that sits atop the bedrock today settled out from the rivers that had flowed through the mountains. Further sand sediments may have been added when the shores of the Champlain Sea rested over our site. Starting about 10,000 years ago, the Champlain Sea receded and the waters between Vermont and New York became less brackish, giving rise to the modern-day Lake Champlain and allowing our site to become a floodplain where the Green Mountains drain into the lake, dropping loamy sediments that made the soil extremely fertile for the farming purposes of some of the Allens, who eventually settled here.

The map below (Poleman) shows the bedrock geology of the entire park as well as the surficial sediments under our site. To the west, the park is underlain by the Dunham Dolostone formation; to the west, Monkton Quartzite. On top of that, a layer of sand shows where the waters of the Champlain Sea lapped the shoreline.

Sources

Frank, Andy.  Quartzite.  Chemeketa Community College geology website.  Retrieved 20 Nov 2011 from .

Poleman, Walter.  Bedrock Geology of Niquette Bay State Park, Colchester, VT.  Map.  Obtained by personal communication.

Thompson, E. and Sorenson, E.  Wetland, Woodland, Wildland.  Hanover: University Press of New England, 2000.