The Geology of Delaware

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Hornerstown Formation

Geologic Time Period: 
Upper Cretaceous and Paleocene
Coastal Plain - Primarily Subsurface Unit

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Glauconite sand that is silty and slightly to moderately clayey and contains scattered shell beds. Glauconite approximately 90 percent to 95 percent of the sand fraction and quartz 5 percent to 10 percent. Near the top of unit, silt-filled burrows are present. Lower, the unit is commonly laminated with silty sand and moderately clayey sand. Silt and clay matrix is calcareous. Uniformly a dark-greenish-gray. Interpreted to be marine in origin. The Cretaceous-Tertiary boundary is considered to lie within the formation. Rarely occurs in outcrop and where shown on the map is covered by colluvium along the stream valley bluffs. Ranges between 10 and 50 feet in thickness.