As the upthrust continued, this granite was exposed through erosion, and became the Appalachian Mountains.

Granite is composed of quartz, mica and feldspar. When it is broken down through erosion, the quartz becomes sand, while the mica and feldspar become clay. These minerals were washed into Appalachian Mountain streams, slowly moving toward the Atlantic Ocean where the forces of waves, wind and shoreline currents shaped the sand into what would become barrier islands and the clay into salt marshes.

Rivers continued to bring sand and clay to the eastwardly-moving coast, creating successive lines of barrier islands and salt marshes. During times when the sea level rose, the coastline moved westward toward the mountains. The rivers continued to add layers of sediment, and the continued repetition of this process through many cycles of sea level rising (as much as 100′) and falling (as much as 300′) created the sandy “skirt” that is two miles deep and flanks the southeastern coast of North America. We now call this area the Coastal Plain.

One hundred thousand years ago, when the formation of polar ice caps caused the sea level to fall and the ocean to recede eastward, Spring Island took shape as a barrier island with high sandy dunes. Twelve thousand years ago, a warming global climate caused sea levels to rise. The shoreline moved westward, reaching its present location approximately 4,000 years ago and Spring Island’s coastal location was established.

The vegetated ancient dune system was located in the middle of the Coastal Plain. The climate was cooler and similar to that of New England. Open oak-hickory savannas dominated the high sandy ridges. In low-lying areas that flooded seasonally, moist soils supported species found in southeastern hardwood bottomland swamp forests such as tulip poplar, red maple, American holly and a variety of oaks, hickories and ash.

In the frequently flooded sections nearest the river, a cypress-tupelo swamp forest grew up. Giant sloths, up to 9′ tall, American mastodons, mammoths, large tapirs, horses and American lions roamed the landscape.

At the end of the ice age Homo sapiens became a dominant part of the landscape. The warmer climate also brought periodic fires, caused by summer lightning strikes. An assemblage of plants adapted to coexist with these periodic fires spread northward out of Florida as the climate warmed.

The dominant plant of this landscape was the longleaf pine. Its long, water-filled needles protected the vulnerable buds of the small saplings and its thick bark insulated the trunks of adult trees. Grasses and small woody plants recovered quickly from passing fires because their buds were below ground. The abundance of long needles from the pines and the dry grasses promoted the quick passage of fires. This killed saplings of other species and the net result was that longleaf forests had a savanna-like appearance. Open landscapes dominated by grasses and low-growing forbs (non-woody, broad-leafed plants) surrounded widely spaced large pines.

A long, thin ribbon of hardwood bottomland swamp forest survives along the slope separating the high sandy areas from the nearby maritime forest. Tulip poplars, swamp chestnut oaks, swamp tupelos and cherrybark oaks dominate the canopy. Fire resistant longleaf pines remain in a north-south strip that runs down the center of the southern section of the Island.

The ocean marched westward as sea level continued to rise, eventually flooding low-lying areas of the present coastline. The Broad River and the tributaries surrounding Spring Island became brackish as fresh water from upstream mixed with the high salinity waters brought inland by the ocean’s tidal pulses. Eventually, the rising sea level inundated the headwaters of the Broad River, transforming this small river basin into a saltwater embayment dominated by rising and falling tides.

This is the area we now know as Port Royal Sound.

This network of deep tidal rivers and creeks can be viewed as watery fingers of the ocean, separated by expansive salt marshes, reaching landward and flooding the landscape twice a day.

Very little sediment is introduced into tidal creeks and rivers because no inland rivers empty into the ocean along this section of the coast. Other coastal estuaries have rivers that originate far inland and transport tons of sediment to the ocean on a daily basis. This sediment has kept the mouth of these other rivers shallow, with numerous shoals.

Spring Island is surrounded by Port Royal Sound, the deepest natural harbor in the southeastern United States. It is an unusual coastal estuary because of its high salinity, exceptionally high tides and very deep waters. Some of its tidal rivers and creeks are as deep as 30-40′.

Due to its geographical location, Port Royal Sound has the highest tides on the southeastern coast. The Sound is located at the center of the Georgia Bight, a curving arc of coastline that extends from Cape Hatteras, North Carolina to Cape Canaveral, Florida. Twice a day a bulge of water created by the gravitational pull of the moon (and to a lesser degree, the sun) causes a high tide. As this tide moves westward across the shallow continental shelf into the Georgia Bight, the height of the tide is amplified until it reaches a high water mark of more than 8′. In contrast, an average high tide in Jacksonville, Florida or Cape Hatteras is approximately 2½′. (Note: The apparent westward movement of the tide is really the eastward rotation of the earth.)

The high salinity provides a diversity of habitats for a variety of crustaceans that become food for many types of fish and birdlife. During the summer months large predators, such as sharks and rays, move up into the deep tidal rivers.

Saltmarsh cordgrass (Sporobolus alterniflorus) is the only plant at this latitude that can survive daily inundation by saltwater tides. It is a perennial and as the dead grass stalks break down each year they provide the nutrients that support the marine food web.

Crustaceans, such as copepods, larval crabs and shrimp, are a critical component of the zooplankton community. In late summer and fall the abundance of adult blue crabs and shrimp supports local fishing industries. At the mouth of the Sound, horseshoe crabs lay millions of eggs that attract thousands of sandpipers migrating between their wintering grounds in southern South America and their arctic nesting grounds.

Zooplankton are eaten by baitfish such as menhaden and mullet which, in turn, feed many of the sports fish that draw anglers to the area. Fiddler crab burrows riddle every salt marsh and the crabs are hunted during low tide by white ibis, night herons and clapper rails and, during high tide, by red drum fish.

Bottle-nosed dolphins patrol the waterways year-round and use a variety of hunting techniques to capture fish. “Strand-feeding” is a particularly remarkable method by which two to four dolphins simultaneously propel themselves up onto the mud of a tidal creek, pushing a wave full of fish in front of them. While lying on their right side they pick up the stranded fish from the creek bank before flopping back into the water and repeating the process. This behavior has been documented only along the coastal tidal creeks of South Carolina and Georgia.

Shell middens are common on Spring Island. Other middens were created in the middle of salt marshes, forming small islands. In a few places, these middens were shaped into a circular wall known as a “shell ring.” Centuries later these discarded shells were used by Americans of European descent to build structures out of “tabby.”

In many locations, decomposing oyster shells have neutralized the acidity of coastal sandy soils.

Ancient shell middens are easily spotted because they support distinctive kinds of plants such as red buckeye, redbud, spruce pine, hophornbeam and mottled trillium. The surrounding acidic soils support forests of live oaks and laurel oaks.