North Carolina Rocks! UNCW’s GeoGarden

North Carolina Rocks! (Literally): An Exploration of UNCW’s GeoGarden

by Ally Zimmerman and Roger Shew

UNCW now has a GeoGarden designed and implemented by faculty member Roger Shew. We interviewed him to learn about the geology of the garden and the inspiration behind it.

North Carolina Geologic Map

This N.C. Geologic Map illustrates the ages, rock types, and source locations of the GeoGarden Rock.

North Carolina’s geology is unique and varies across three main regions of the state: Blue Ridge, Piedmont and Coastal Plain. North Carolina also has a long geological history; in the western part of the state, there are rocks greater than one billion years old! Here in Wilmington, the GeoGarden at the University of North Carolina Wilmington (UNCW) provides a unique opportunity to view rocks from all three regions of North Carolina.

This garden, located on UNCW’s campus, contains rocks from across the state of North Carolina ranging from the Fort Fisher Coquina along the Coast to the Spruce Pine Pegmatite in the Blue Ridge Mountains. Not only does the GeoGarden provide a unique opportunity to view geology from across the state, it also features stormwater management with a “streambed” and rain garden. The rain garden helps collect rainwater from the roof of DeLoach Hall and surrounding grounds to help prevent polluted runoff from getting into the Bradley Creek since most of the UNCW campus is in the Bradley Creek watershed.

The cistern, or large rain barrel, at the western end of the GeoGarden collects stormwater from the roof of DeLoach Hall. A solar-powered pump helps move the water through a hose to water plants in the rain garden during periods of little or no rain.

photo by Valerie Robertson

Stormwater in the GeoGarden

One of the important ecological and educational aspects of the GeoGarden is its stormwater mitigation features, including a streambed and rain garden. The streambed flows from west to east funneling water from gutters and the surrounding area into the rain garden. The rain garden was constructed in the shape of a Carolina Bay. Carolina Bays are oval wetlands and bay lakes commonly found in the Coastal Plain; Jones Lake and White Lake are examples. The northwest to southeast orientation and length-to-width ratio of Carolina Bays was the inspiration for designing the rain garden. There is also native vegetation such as cypress, sweet bay and palmetto incorporated in the rain garden.

The base of this downspout was cut off and extended so that rainwater from the roof of DeLoach Hall would flow into and down the dry stream of rocks. The water moves into the rain garden at the end of the garden, where accumulated water can seep slowly into the ground.

photo by Roger Shew

Inspiration for the GeoGarden

The beautiful DeLoach GeoGarden was implemented by Roger Shew, a professor at the University of North Carolina Wilmington in the department of Earth and Ocean Sciences. The goal and inspiration of the project is to provide an educational opportunity for students at the University, nearby schools and the community. Roger Shew’s plan is to have schools come visit to see and feel a bit of North Carolina and understand the geologic richness and resources of our state. In addition to the geologic knowledge, other educational benefits include the stormwater management function and the native plants that have been planted in the garden area.

Two amazing efforts that are still in progress include finishing signage for the site and the construction of a website that will provide online information about North Carolina as well as a curriculum for school-aged students and teachers to use. Roger Shew hopes that the site will be used for many years. He attended UNCW as an undergrad and has taught there for 20 years. The GeoGarden is one way for him to give back to the community where he grew up and to the wonderful UNCW community.

Effectiveness of a Working Rain Garden

The stormwater mitigation features have proven effective in handling more than three inches of rain in a 24-hour period, which is well over stormwater design requirements. The image directly below illustrates the area holding that volume of water; the image beneath it shows that complete infiltration had occurred by the following day.

Rainfall 9/22/21; Time 3 p.m. 5.61 inches of rain in 2 days and 3.96 inches in last 24 hours.

photo by Roger Shew

9/23/21; Time 10 a.m. Just hours later, all of the water had infiltrated and no water went into the square overflow.

photo by Roger Shew

About the rocks

The rocks within the GeoGarden are positioned just as they occur in the state. Rocks from the mountains occur at one end of the “trail” and the rocks follow the geologic provinces from west to east ending at the Coast. You can start at either end of the trail to study the rocks. The Spruce Pine Pegmatite is the most westerly occurring rock from the Blue Ridge Province and the Fort Fisher Coquina is the most easterly occurring rock on the beach in the Coastal Plain. There are a total of ten rocks in the display; all donated by quarries or individuals. The rocks represent all three rock types: igneous, metamorphic and sedimentary rocks. Many of them are also important rock and mineral resources including granite, feldspar, aggregate, phosphate, pyrophyllite, diabase and even an aquifer. Below is a list of the rock types in the GeoGarden: the first rock type is the farthest east and the last is the farthest west.

Fort Fisher Coquina: The coquina is the only rock outcrop (exposed rock) on the beach in North Carolina. It is 55,000–70,000 years old, from the Pleistocene, and is composed of broken shell material and minor quartz sand. The Fort Fisher site is a designated State Heritage Location.

Aurora Quarry Phosphate: The Aurora Quarry is a very large quarry near Aurora, North Carolina where phosphate mining occurs. The age of the sediments and rocks is 2–15 million years old from the Pliocene to Miocene epoch. Phosphate is commonly used for phosphoric acid and fertilizer. North Carolina has the second largest source of phosphate in the United States and the Aurora Quarry is world famous for its numerous, well-preserved marine fossils including whale vertebrae, mollusk shells and Carcharodon megalodon shark teeth, the North Carolina State Fossil.

Castle Hayne Limestone: This rock is primarily limestone that formed in normal marine waters approximately 40 million years ago during the Eocene age. The Castle Hayne Limestone is an important aquifer in New Hanover and Brunswick counties and is also a major source of aggregate for roadways. The rock contains numerous fossils including mollusks, gastropods, echinoderms and bryozoans.

Petrified Wood: Petrified wood is found along the Cape Fear River and was formed 70+ million years during the Cretaceous age. Silica has replaced the original wood fabric preserving some of the tree’s rings and fabric.

Diabase: The diabase is an igneous rock found in the Triassic basins of North Carolina that formed ~180 million years ago during the Triassic age. This rock is primarily used for aggregate in construction.

Pyrophyllite: Sedimentary mudrocks were metamorphosed to form the pyrophyllite. The rock is smooth and soft, similar to talc. It is used in refractory processes and in ceramics.

Lilesville Granite: The granite is characterized by having large crystals of quartz, feldspar and biotite. The most distinctive mineral is the pink feldspar. The large crystals indicate that the magma cooled slowly, which is the only way to form large crystals. The igneous rock formed approximately 325 million years ago during one of the convergent mountain building episodes.

Mount Airy Granite: The Mount Airy Granite is an intrusive igneous body of rock that was formed 355–390 million years ago. It is composed of quartz, feldspar and biotite. Granite is the state rock of North Carolina and the Mount Airy Quarry is the largest openfaced granite quarry in the world. Its uniform composition has allowed it to be used in the Wright Brothers Monument, the Fort Knox Bullion Depository and the WWII Memorial in Washington, D.C.

Marion Metamorphic Rock: The Marion rock was once a layered sedimentary rock that has been metamorphosed. There is abundant mica forming the foliation of the rock. The dominant use is for building stones and decorative rock work.

Spruce Pine Pegmatite: Spruce Pine Pegmatite is an igneous intrusive rock with large crystals of feldspar, quartz and mica. The rock was formed ~320–380 million years ago during the Paleozoic Era. North Carolina is the largest source of feldspar in the United States and Spruce Pine is considered the rock and mineral capital of North Carolina. The surrounding area contains numerous mines with valuable resources, including the Spruce Pine Pegmatite.

For more information on the natural history of North Carolina see article on page 8 of this issue.

How to visit the GeoGarden

The GeoGarden is located next to DeLoach Hall on the University of North Carolina Wilmington campus. Shew would be happy to lead tours but the garden is open and accessible at any time. Once there are informational signs added, the garden will be somewhat self-guiding. The path is easily accessible through the garden and is wheelchair friendly, but visitors should be careful of a few slightly uneven surfaces with pebbles. Visitors should not climb on the rocks although leaning on them and studying them is fine.

This view looks from youngest Coastal Plain rocks, beginning with Fort Fisher Coquina in the east, moving across the state to the Blue Ridge rocks and ending with Spruce Pine Pegmatite at the western end. The rain garden and streambed appear to the right in the the image.

photo by Roger Shew

The GeoGarden presents a unique opportunity to view how geology differs across North Carolina. If you are interested in seeing this wonderful garden, be sure to visit the UNCW campus!

The UNCW campus is located at 601 South College Road in Wilmington, North Carolina. The GeoGarden is next to DeLoach Hall, just past Kenan Auditorium.

Roger Shew is in the Earth and Ocean Sciences and Environmental Sciences Departments at UNCW. Ally Zimmerman is a senior at the University of North Carolina Wilmington studying political science and environmental science with a concentration in conservation. She is an intern with Going Green through UNCW’s Environmental Sciences Department.

The fossil pit in the GeoGarden contains a variety of the typical rocks and fossils from the Aurora Quarry. The rocks are mostly limestones and sandy limestones, but there are also samples of the black phosphate rocks that are mined as a resource. The fossils include coral, mollusk shells, mammal vertebrae and a variety of shark teeth. Digging through the fossil pit may yield a quality fossil for someone to take home.

photo by Valerie Robertson