The seas retreated, leaving a thick seabed behind that was gradually covered over with coastal sands and flood deposited silt from what is now the Cape Fear and NE Cape Fear rivers.

The limestone has great commercial value, in aggregates and cement, and Martin Marietta operates a large quarry near Castle Hayne, NC.

A couple of afternoons each week, Martin Marietta allows fossil hunting in the spoil areas, the fossil rich layers of soil overburden that must be pushed aside to reach the limestone.

On my first visit I met a few members of the NC Fossil Club, and they gave me an overview of the area, what I might find, and which deposits contain certain fossils. 

Unfortunately, on my second visit, after only about 15 minutes, I raked through the sand pile I was exploring and pulled out this beautiful 'trophy' echinoid, at top. I say unfortunately because now I'm hooked, and look forward to each visit to expand my range of explorations, and learning more about the what and why and how this one-time shallow sea.

The overburden is arranged in rows, and away from the quarry pit. The quarry rules are simple enough: stay out of and away from the quarry pit, and stay out of everywhere marked with no access signs. 

After you drive down the fossil area access road, you'll find a large pile of sand, and this is where I found the echinoid in the top picture. Drive a little further and park, and you can enter the rows of overburden piles seen in the second picture.

Look carefully and you'll see that some of the piles are darker, and these piles contain dark green phosphate mineral, nodules formed possibly by nitrate fixing bacteria, possibly Thiomargarita. These piles seem to have more and larger shark's teeth than the other piles.

Some more piles are notably whiter, and contain more chalky-looking sediments, and with more shells and bryozoan fragments.

In the larger limestone rock, there are impressions of where the shells were, and it seems the calcium carbonate shell has dissolved and been transformed into calcite mineral, clear small crystals deposited on the inner surface of the cavity.

(Note: if you're a student and take anything I might write as the basis for science fact, you're going to be in trouble. I'm an enthusiastic amateur, without discipline or direction, striving to understand a little something about the stuff I'm looking at, but being unburdened by the need for strict academic rigor, or course requirements for accuracy.)

Try as I might, understanding the words of geology and paleology-speak * doesn't come easy.

In the excerpt below, there is discussion of the lithostratigraphic (arrangements of rock layers) characteristics of the Castle Hayne Formation.

There are three member layers:

The New Hanover Member is the lowest, and darkest.

The Comfort Member is in the middle, and contains bryozoans and echinoids.

The Spring Garden Member is on top, with mollusks

There's a picture near the bottom that shows the layers. There is a marked difference in the type of deposits above and below the middle seam of chalky deposit.

* Rarely seen coleoid phragmacone steinkerns from the Eocene Castle Hayne Limestone of southeastern North Carolina

Near-surface deposits of the middle Eocene Castle Hayne Limestone extend as a 16-32 km wide zone from Brunswick County and New Hanover County north through east-central Pender County, through western portions of Onslow, Jones and Craven Counties, and into southeastern Pitt County in southeastern North Carolina (Otte, 1986). Bounded by unconformities above and below, the formation is typically overlain by Oligocene and younger rocks and underlain by Paleocene and Cretaceous rocks. The Castle Hayne Limestone is thought to range in age from mid-Lutetian to Priabonian (Harris and Laws, 1997). Baum et al., 1978; Ward et al., 1978; Kier, 1980, Zullo and Harris, 1986 and 1987; and Harris and Zullo, 1987, have interpreted the lithostratigraphic subdivisions of the Castle Hayne Limestone. Ward et al. (1978) named three lithosomes within the Formation (New Hanover, Comfort and Spring Garden Members). The lowest unit (New Hanover Member) is a slightly arenitic, micritic and phosphatic lithocalrudite; the middle unit (Comfort Member) is a gray to cream colored bryozoan-echinoid calcirudite, grading to a fine calcarenite; and the uppermost unit (Spring Garden Member) is a tan to gray arenaceous molluscan-mold biocalcirudite. All units typically represent differing time sequences at different exposures.

Applying a sequence approach, Harris and Zullo (1987) divided the Castle Hayne Limestone into five depositional sequences (0-4). These sequences, divided by regional unconformities, reflect sea-level and depositional environmental change. A complete lithologic section consists of a phosphate pebble biomicrudite base overlain by biosparudite, in turn overlain by biomicrudite grading into biosparudite. A complete lithostratigraphic section is rarely represented at a single locality and sequences are typically represented by different lithologies at various exposures.

Using an echinoid-based biostratigraphic approach, Kier (1980) divided the Castle Hayne Limestone into three informal biozones (early, middle, late).These temporal biozones overlap somewhat with the depositional sequences defined by Harris and Zullo (1987) and provide a reasonable biostratigraphic interpretation. Correlation between sequence stratigraphy (Harris and Zullo, 1987), biostratigraphy (Kier, 1980) and lithostratigraphy (Ward et al., 1978) is provided in Text-figure 1.

Stratigraphic location within the Castle Hayne Limestone is not precisely known, but based on where in the quarry the specimens were collected, coupled with the presence of Periarchus lyelli and the lithologic composition of the phragmacone steinkerns, it is likely that these specimens were contained within sequences 3 or 4 (Zullo and Harris, 1987).