The Red Clay Creek has flowed through the rolling hills of northern Delaware for many thousands of years, cutting a deep valley into the old deformed rocks of the Appalachian Piedmont. The Red Clay valley contains many of the common rocks found throughout the Delaware Piedmont.
In Delaware, predominantly a pure, coarsely crystalline, blue-white dolomite marble interlayered with calc-schist. Major minerals in the marble include calcite and dolomite with phlogopite, diopside, olivine, and graphite. Major minerals in the calc-schist are calcite with phlogopite, microcline, diopside, tremolite, quartz, plagioclase, scapolite, and clinozoisite. Pegmatites and pure kaolin deposits and quartz occur locally.
Sinkholes are depressions in the land surface or holes in the ground caused by subsidence or collapse of surficial material into openings in soluble rock. Sinkholes usually develop in "karst" areas underlain by carbonate rocks. Karst is defined as "terrane with distinctive characteristics of relief and drainage arising primarily from a higher degree of rock solubility in natural waters than is found elsewhere" (Jennings, 1971, p.1). In addition to sinkholes, other features associated with karst are: caves, disappearing streams, and well-developed subsurface drainage systems.
This Bulletin presents the subsurface stratigraphy of the post-Potomac Cretaceous and Tertiary rocks of the Atlantic Coastal Plain of central Delaware, between the Chesapeake and Delaware (C & D) Canal and Dover. Geophysical log correlations supported by biostratigraphic and lithologic data from boreholes in Delaware and nearby New Jersey provide the basis for the report.
The non-marine Cretaceous sediments of northern Delaware older than the Magothy formation cannot be divided accurately into formations or mappable geologic units because their lithologic characteristics are very similar. However, two heavy mineral zones can be distinguished in these deposits: a lower staurolite-kyanite-tourmaline-zircon zone, and an upper tourmaline-zircon-rutile zone with abundant alterites. They have been named the Patuxent zone and the Patapsco-Raritan zone respectively.
The State of Delaware is located within two physiographic provinces, the Appalachian Piedmont and the Atlantic Coastal Plain. The Fall Zone divides these two provinces and essentially runs parallel to Delaware Rt. 2, Kirkwood Highway.