The Castle Hayne Formation is divided into three submembers: the New Hanover member, the Comfort Member, and the Spring Garden Member. The New Hanover member is the oldest member and is characterizes by cobbles and pebbles, fine sand, glauconite, and phosphate in a fine limestone matrix. The most common fossils are shark and ray teeth.
Index fossils place this member in the middle Eocene. The Comfort member lies above the New Hanover member. It contains
bryozoa and
sea urchin fossils and beds of glauconite and phosphate pebbles that mark breaks in deposition. The Comfort member was deposited in the late middle Eocene and is overlain by the Spring Garden member. The Spring Garden member is a
siliceous rock cemented with
calcite and containing detrital phosphate. Mollusc bivalves account for up to 75% of the composition in some areas and molds of molluscs shells filled with silica are common. Index fossils indicate this member was also deposited in the late middle Eocene. == Vertebrate paleobiota ==