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Soils and sediment in Shelburne
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Between the bedrock and landscape surface of Shelburne lies a layer of sediment and soil, uncemented geologic material that has great influence over the vegetation and human activities in the region. Sediment, or "surficial" material, consists of clay, sand, and gravel deposited by geologic processes (see below). Soil is formed through a combination of eroded and weathered geologic material, and decaying plant matter. The chemical and physical composition of the soil helps determine what natural vegetation and crops will grow in a certain place. (Maps courtesy of Shelburne PLACE program)
Surficial deposits
As the glaciers retreated from the Champlain Valley, they left behind a layer of jumbled rock, gravel, and sand known collectively as "till". The expansive glacial lakes that subsequently covered the valley left behind a thick mantle of clay. As rivers such as the Winooski were re-established, further layers of sand and gravel were deposited.

The map at left shows the major units of surficial material in Shelburne. Most of the region is covered in a thick mantle of marine clay (brown), which contributes to the productive, nutrient-rich soil of the area. The wide swath of sand and gravel (orange) running north-south through the center of town represents an old shoreline, where sediment was deposited in deltas and beaches along the waterline. There are also isolated deposits of glacial till (red).

Surficial map of Shelburne.
Soils
Along with climate, soil is the dominant factor affecting where different types of vegetation can grow. Soil is affected by the underlying bedrock and surficial material, from which soil gets much of its mass. For example, soils forming from a calcium-rich rock such as limestone or a nutrient-filled surficial material like clay will support a great deal of vegetation and diverse agriculture. Soils forming from acidic or nutrient-poor sources such as sandstone or glacial till tend to support less vegetation and agriculture.

The soils map on the left illustrates this relationship. While there are a great deal of different soil types plotted on the map, some general trends are clear. The richest soils, shown in red and aqua, exist in areas underlain by shale, limestone, and/or clay, and are areas of agriculture and well-developed forest. The poorer soils, shown in brown, overlie areas of sandstone and till, supporting more tolerant vegetation such as pine forests.

Soils map of Shelburne
Local Soils