Just northwest of the confluence of Mill Creek and an unnamed tributary is an abandoned quarry. This quarry sits off the greenway trail, across from a ruined foundation wall, and displays samples of black, coarse-grained, foliated amphibolite. The unnamed tributary and Mill Creek are choked with amphibolite rocks and boulders. The amphibolite here weathers with a rusty rind and has a foliation strike of 10 degrees east of north and an obviously steep to vertical dip.
Mill Creek Metagabbro
Coarse-grained gabbroic and metagabbroic rocks, variably metamorphosed and deformed. Primary minerals are hornblende and plagioclase.
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.
All the rock units in Delaware’s Piedmont are highly deformed. Deformational features, such as folds, faults, and/or joints, are present in almost every outcrop.
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.
This is a map of the crystalline bedrock units in the Piedmont of Delaware and adjacent Pennsylvania. The southern boundary of the mapped area is the updip limit of the Potomac Formation (Woodruff and Thompson, 1972, 1975). Soil, regolith, and surficial deposits of Quaternary age are not shown.