First State Geology has been the newsletter of DGS for over 25 years. 
The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:
Light- to dark-gray, very micaceous, glauconitic, very silty fine- to very fine-grained sand to fine sandy silt. Ranges from 20 to 120 ft in thickness. Marine in origin.
