The Nanjemoy Formation (Early Eocene - Ypresian) is made up of two members, the Potapaco and Woodstock.

The clayey sands and fauna of the primary collecting locale suggest a near shore (100-200m) marine environment. This fauna is rich in vertebrate fossils -- producing material from fishes, reptiles, birds and occasionally, land mammals. Besides abundant chondrichthyan teeth, this is one of the few locations where sea snake vertebrae may be deemed common.

Mantell's Iguanodon restoration