The Castle Hayne Limestone (also called the Castle Hayne Formation) is a middle Eocene-aged geologic formation in North Carolina, USA.

[1] It consists of cobble to pebble sized clasts, usually rounded, coated with phosphate and glauconite in a limestone matrix.

It contains bryozoa and sea urchin fossils and beds of glauconite and phosphate pebbles that mark breaks in deposition.

The Spring Garden member is a siliceous rock cemented with calcite and containing detrital phosphate.

Index fossils indicate this member was also deposited in the late middle Eocene.