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Site content related to keyword: "Brandywine Blue Gneiss"

Outcrop Bd42-e: The Cliffs of Alapocas Woods

Rock Outcrop Bd42-e: The Cliffs of Alapocas Woods

Located in Wilmington, DE, the Cliffs of Alapocas Woods are opposite the old Bancroft Mills across the Brandywine Creek. Along the creek you will find large exposures of Brandywine Blue Gneiss. Compared to other outcrops in the Piedmont of Delaware, the rock examples here are massive. When observed closely, the felsic gneiss displays a medium grain size. Most of early Wilmington was built from the stone from these quarries. These impressive rock features are enjoyed by local rock climbers as well as many who use the Northern Delaware Greenway.

Bellevue State Park (BVD) Seismic Station

Bellevue State Park (BVD) seismic network station. The seismometer located at Bellevue State Park is placed on the Brandywine Blue Gneiss. The Brandywine Blue Gneiss is the new name given to the granulite-facies felsic gneisses in the Wilmington Complex. Informally called the “blue rocks,” this unit is a medium- to coarse-grained, lineated (pinstriped), two-pyroxene gneiss with variable quartz content and thin, discontinuous mafic layers, pods, and schlieren. The pinstriping and the massive nature of the rock suggest the rock is intrusive; however, deformation and recrystallization have obscured original igneous features.

Brandywine Blue Gneiss

Obbg

Medium to coarse grained granulites and gneisses composed of plagioclase, quartz, orthopyroxene, clinopyroxene, brown-green hornblende, magnetite, and ilmenite. Mafic minerals vary from < 5-30 modal percent. A lineation due to a preferred orientation of quartz and mafic minerals is obvious on weathered surfaces. Unit contains thin, discontinuous fine-grained mafic layers.

Exploring the Wilmington Blue Rocks: A GeoAdventure in the Delaware Piedmont

Blue Rocks at Greenway

The Wilmington blue rock, Delaware's most famous rock, underlies both the city of Wilmington and the rolling upland north and east of the city. It is best exposed along the banks of the Brandywine Creek from south of Rockland to the Market Street Bridge. Along this section the Brandywine has carved a deep gorge in the blue rock. The water fall along this four mile gorge is approximately 120', and in the 17th and 18th centuries provided water power for one of the greatest industrial developments in the American colonies. The field trip stops described below are chosen as good examples of blue rock along the Brandywine Creek, and to illustrate how the geology has influenced the development of this area. It is not necessary to visit every stop to become familiar with the blue rocks, you may choose to visit only a few.

GM13 Geologic Map of New Castle County, Delaware

GM13 Geologic Map of New Castle County, Delaware

This map shows the surficial geology of New Castle County, Delaware at a scale of 1:100,000. Maps at this scale are useful for viewing the general geologic framework on a county-wide basis, determining the geology of watersheds, and recognizing the relationship of geology to regional or county-wide environmental or land-use issues. This map, when combined with the subsurface geologic information, provides a basis for locating water supplies, mapping ground-water recharge areas, and protecting ground and surface water. Geologic maps are also used to identify geologic hazards, such as sinkholes and flood-prone areas, to identify sand and gravel resources, and for supporting state, county, and local land-use and planning decisions.

Map Scale: 
100,000
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