One is a preserve, the other a play-ground. Sue Halpern has twice the fun exploring the separate fates of twin isles, Amelia and Cumberland

An armadillo is waggling across the dirt track that passes for a road on Cumberland Island, Georgia's southernmost barrier to the sea. It's moving so slowly that the jeep I'm riding in—what passes for traffic here—has come to an abrupt halt. It's a Marlon Perkins moment as the strangely articulated animal pauses not three feet from seven gaping humans and offers a long, absentminded stare, an "I think perhaps we've met, but when?" kind of look, before giving up and snuffling a palmetto. To be completely accurate, only six of us are speechless. The seventh, a local naturalist who is idling patiently in the driver's seat, says, "Armadillos didn't come to Cumberland until 1974. They got here by inflating their intestines and floating across the water."

For the past three hours, as the jeep followed the beach, he has offered up bits of wisdom like this in between a constant patter of "black scoot," "wild turkey," "osprey," "cedar waxwing," "bladderwort," "slash pine," "great blue heron," and "brown pelican" that keeps us rubbernecking. He was the resident naturalist at the 17-room Greyfield Inn, the island's only hotel, and armadillos, alligators, and eagles, to say nothing of crevasse-mouthed humans, were his bread and butter. Cumberland (population: 50; size: Manhattan) is as close to a pristine wilderness as there is anymore, a place where wild horses, white-tailed deer, and ibis outnumber humans, who can be counted among the rarest of species. So the armadillo's bewilderment at seeing us makes a certain amount of sense.

But guess again, our naturalist says. It's something else altogether. Armadillos have crummy eyesight. To them we might be trees.

Trees dominate Cumberland—pines and palms, to be sure, but live oaks even more so. Shawled with Spanish moss, they emanate that deliciously eerie feeling of nature untamed and looming. Though open water is never more than a mile and a half away, the thick huddle of oaks, with their understory of saw palmetto, make this seem like the forest primeval.

That it is not, but seems so, is one of those rare and happy collisions of time and money. The money belonged to Thomas Carnegie, brother of Andrew and a wealthy Pittsburgh industrialist in his own right. The time was the late nineteenth century, about a hundred years after the island's trees had been cut down to make way for cotton plantations, when Carnegie, at the behest of his wife, began buying up Cumberland for a vacation retreat. Today, trees have reclaimed the island and there is little evidence of its brief—geologically speaking—cultivated past.

It is this past that we are discussing, first in the jeep, as we stop at the African Baptist Church, made famous by the wedding of John Kennedy, Jr., and Carolyn Bessette in 1996, just three years before their deaths. A shoebox of a building, its paint peeling and clapboard decaying, it is the last remnant of a community of freed slaves and their descendants, who lived on the island long after its plantations were overrun by ironwood. We eat lunch on the church steps—turkey sandwiches, cranberry couscous, and fully chocked chocolate chip cookies supplied by the cooks at Greyfield—pulling the provisions out of wicker picnic hampers as if they were prizes, which they are.