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DGS Annual Report

DGS Annual Report of Programs and Activities.

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Site content related to keyword: "Rockford Park Gneiss"

Outcrop Bd41-b: Rockford Park Gneiss Boulders at Rockford Park

Rock Outcrop Bd41-b: Rockford Park Gneiss Boulders at Rockford Park

The Rockford Park boulders can be found just beyond the Rockford Tower on the slope facing the Brandywine Creek. Some areas of the Rockford Park Gneiss actually display some banding of felsic gneiss and mafic gneiss which are interlayered on a scale of 4" to 2'. This banding strikes 30 degrees east of north and dips 60 degrees to the northwest. The mafic layers are boudinaged and broken, some of which are weathered away into a prominent relief. Between some layers, the rock is intruded by a coarse-grained and apparently undeformed gabbro.

Rockford Park Gneiss

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Fine-grained mafic and fine- to medium-grained felsic gneisses interlayered on the decimeter scale. Layers are laterally continuous, but mafic layers commonly show boudinage. Felsic layers are composed of quartz and plagioclase with < 10 modal percent pyroxene. Mafic layers contain subequal amounts of plagioclase, pyroxene, and hornblende. Penetrative deformation and granulite facies metamorphism have obscured igneous fabrics and contact relationships.

RI59 Bedrock Geology of the Piedmont of Delaware and Adjacent Pennsylvania

RI59 Bedrock Geology of the Piedmont of Delaware and Adjacent Pennsylvania

This report accompanies a new map that revises the original bedrock geologic maps of the Delaware Piedmont compiled by Woodruff and Thompson and published by the Delaware Geological Survey (DGS) in 1972 and 1975. Combined detailed mapping, petrography, geochemistry, and U-Pb geochronology have allowed us to redefine two rock units and formally recognize eleven new units. A section of the Pennsylvania Piedmont is included on the new map to show the entire extent of the Mill Creek Nappe and the Arden Plutonic Supersuite.

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.

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