Ironshire Formation

The Ironshire Formation was described by Owens and Denny (1979) as consisting of a lower loose, pale-yellow to white, well-sorted, medium sand characterized by long, low-angle inclined beds with laminae of black minerals. The upper portion of the units was described as consisting of light-colored, trough cross-stratified, well-sorted sand with pebbles and a few Callianassa borings. They described the Ironshire Formation near Rehoboth in a stratigraphic section which is now considered to be a part of the Lynch Heights Formation.

Wissahickon Formation

Interlayered psammitic and pelitic gneiss with amphibolite. Psammitic gneiss is a medium- to fine-grained biotite-plagioclase-quartz gneiss with or without small garnets. Contacts with pelitic gneiss are gradational. Pelitic gneiss is medium- to coarse-grained garnet-sillimanite-biotite-plagioclase-quartz gneiss. Unit has a streaked or flasered appearance owing to the segregation of garnet-sillimanite-biotite stringers that surround lenses of quartz and feldspar. Throughout, layers of fine to medium-grained amphibolite composed of plagioclase and hornblende, several inches to

Ardentown Granitic Suite

Medium- to coarse-grained granitic rocks containing primary orthopyroxene and clinopyroxene; includes quartz norites, quartz monzonorites, opdalites, and charnockites. Feldspar phenocrysts common. Mafic enclaves locally abundant in proximity to gabbronorites.

Lynch Heights Formation

Heterogeneous unit of light-gray to brown to light-yellowish brown, medium to fine sand with discontinuous beds of coarse sand, gravel, silt, fine to very fine sand, and organic-rich clayey silt to silty sand. Upper part of the unit commonly consists of fine, well-sorted sand. Small-scale cross-bedding within the sands is common. Some of the interbedded clayey silts and silty sands are burrowed. Beds of shell are rarely encountered. Sands are quartzose and slightly feldspathic, and typically micaceous where very fine to fine grained. Unit underlies a terrace parallel to the present Delaware Bay that has elevations between 50 and 30 feet. Interpreted to be a fluvial to estuarine unit of fluvial channel, tidal flat, tidal channel, beach, and bay deposits (Ramsey, 1997). Overall thickness ranges up to 50 feet.

B20 Stratigraphy of the Post-Potomac Cretaceous-Tertiary Rocks of Central Delaware

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.