DGS Annual Report

DGS Annual Report of Programs and Activities.

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Site content related to keyword: "Brandywine Creek State Park"

Gaining new appreciation of rocks in the garden

Stone walls near Brandywine Creek State Park are built of native fieldstone, including amphibolites and Brandywine granite, or gneiss, which gave the Wilmington Blue Rocks baseball team its name. / News Journal file/ROBERT CRAIG

Gardeners from northern New Castle County should be grateful that the glaciers stopped their descent at the Delaware Water Gap about 100,000 years ago.

Outcrop Bd21-a: Boulder Field at Brandywine Creek State Park

Rock Outcrop Bd21-a: Boulder Field at Brandywine Creek State Park

In the patch of woods north of the upper parking lot in Brandywine Creek State Park, there are large outcrops of amphibolite. The outcrops are rounded from exfoliation, and are black with few structural features. The mafic hornblende grains are elongated parallel to a few thin felsic bands. This lineation strikes east-west and dips to the north. These boulders are located on the northwest facing slope of the valley and are probably a paraglacial feature left over from a colder period in Delaware's geologic past.

Seismic Network Map

The DGS maintains its own network of seismometers to detect local earthquake activity. Following an earthquake swarm in 1972, the DGS established its first seismometer station in Newark. The network now consists of five seismic stations spread across the state: three stations in the Newark-Wilmington area, one at the DEMA office in southern New Castle County, and one at the Sussex County Emergency Operations Center.

Brandywine Creek State Park (BWD) Seismic Station

Brandywine Creek State Park (BWD) Seismic Station. The seismometer located at Brandywine Creek State Park is positioned on the Wissahickon Formation. The Wissahickon Formation is an extensive sequence of pelitic and psammitic gneisses interlayered with amphibolites. With few exceptions, most of the amphibolite layers are less than 30 feet thick. The rocks have been metamorphosed to upper amphibolite facies and isoclinally folded. The formation is located within the Wilmington North, Kennett Square, West Grove, Newark West, and Newark East quadrangles.