Delaware

Tower Hill
       7½’ quadrangle: Wilmington North, DE-PA
       New Castle County
       Private property. (check www.Highpointers.org for access information)

Metamorphic (metamorphosed igneous)
442 ft (135 m)

Bedrock: No rock exposed at surface.
Underlying bedrock is Ordovician.
Rockford Park Gneiss, Wilmington Complex

Ordovician

Fine-grained mafic and felsic gneiss, interlayered at the decimeter scale. The mafic layers contain plagioclase, pyroxene and hornblende, and are commonly boudinaged. The felsic layers contain quartz, feldspar and less than 10% pyroxene. Original igneous textures are obscured by a penetrative foliation and granulite metamorphism. The body of Rockford Park Gneiss at the highpoint is surrounded by the Brandywine Blue Gneiss, which is overall more felsic. Foliation dips moderately to steeply northwest. The Wilmington Complex is separated from metasedimentary rocks a few miles west by the Rosemont shear zone, a major boundary showing dextral fault motion, one of many in a complicated system of faults that sheared up the Laurentian margin during docking of Avalonia.

Surficial Geology: Not glaciated.

Soil Series: Neshaming and Montatto silt loams: Shallow, two to four feet to bedrock, developed on weathered mafic and felsic metamorphic rocks under oak and hickory forests.

Selected References:

  • Maguire, T.J. and others, 1999, Continuation of Appalachian Piedmont under New Jersey Coastal Plain, in Valentino, D.W. and A.E. Gates, The Mid-Atlantic Piedmont: Tectonic Missing Link of the Appalachians: Geological Society of America Special Paper 330.
  • Matthews, Earle D. and others, 1970, Soil Survey of New Castle County, Delaware: U.S. Soil Conservation Service.
  • Schenck, W.S., M.O. Plank and L. Srogi, 2000, Bedrock Geologic Map of the Piedmont of Delaware and adjacent Pennsylvania: Delaware Geological Survey, Geological Map Series No.10, 1:36,000.
  • Valentino, D.W., 1999, Late Paleozoic dextral transpression, crystalline core of the Pennsylvania reentrant, in Valentino, D.W. and A.E. Gates, The Mid-Atlantic Piedmont: Tectonic Missing Link of the Appalachians: Geological Society of America Special Paper 330, p.59-71.

Other suggested sources of information:


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