How long till American beaches, like American cigarette packs, carry a government warning label? “Danger: Exposure to the sun may cause skin cancer. Sand in amounts sufficient to block breathing passages will cause asphyxiation. Prolonged submersion beneath the surface of water without countervailing apparatus causes death. The ­one-­hot-­dog limit is enforced by radar.”

The innocence is off the excursion. Remember when a day at the beach was something to look forward to, an occasion for the family to participate in a ritual as fixed as any in a house of worship, or for teenagers to gather in pairs to confirm a passion or shift its allegiance? Now the immortalitarians have had their say: A sunny afternoon at the ­beach—­heck, a bright ­hour—­is pretty much a crapshoot with death, as alarming as trans fats or Dr. Phil. The blithe old song might as well have been advising seppuku: “Just direct your feet/To the sunny side of the street.” Sure, you can coat yourself in lotions with SPF numbers approaching triple digits and names like Mummy and Burka, but can you be absolutely certain you haven’t left a fleshy chink in the chemical ­armor?

On the other hand, as in response to so much other good ­advice—­vote; learn to tell the difference between Kurdistan and Kyrgyzstan; come to terms once and for all with the Brussels sprout; adopt a ­glacier—­we may choose instead to follow our wayward hearts. And pack the cooler and grab the blanket and folded lounge chairs and iPod and indispensable little phone unit, and make straight for the sand.

But don’t take a poet. Beaches cause poets to inflate like vatic bullfrogs. Matthew Arnold, for instance, staring at the pebbly, moonlit beach in Dover, saw the “naked shingles of the world,” and heard “the eternal note of sadness” and the “melancholy, long, withdrawing roar” of the Sea of Faith, and imagined a world where there was “neither joy, nor love, nor light,/Nor certitude, nor peace, nor help for pain.” I’m guessing there was no smoothie shack on Dover ­Beach.

Even Robert Frost wasn’t ­immune:

Great waves looked over others coming in,

And thought of doing something to the ­shore

That water never did to land ­before. . . .

It looked as if a night of dark ­intent

Was coming, and not only a night, an ­age.

Someone had better be prepared for ­rage.

(“Once by the Pacific”)

For me, unlike for an agitated poet, a beach has always been a perfect setting for lazy reverie, for thoughts drifting in and out of focus. The origin of the word “beach” is itself unclear, having been wiped from the record as if . . . as if it had been written on sand in the path of a wave. Water has its way with a shore; if you can’t step into the same river twice, neither can you step twice onto the same beach. No matter how familiar, the place is always new. An empty beach can have the purity of a blank page, on which anything might be set down; a crowded beach, the expectancy of a stage with lots of players enacting simultaneously their tiny individual dramas. Most of the playlets will end with the afternoon, but while they’re being enacted, they’re ­all-­consuming. That’s because a beach is a ­self-­contained world, at an absolute remove from the settings of ordinary life. It’s a ­Janus-­y world, too, and edgy. It positions you at the end of land and its beginning, at the beginning of water and its end. But the ­division—­land here, water ­there—­is always under negotiation, resulting in a sometimes unpredictable mingling of the two. In that damp conjunction, somewhere, surely, there’s a lesson for ­life.

It may be time to go ­indoors.

You may not think of beaches when you think of New York City, but you should. Manhattan and Staten are islands, after all, and Brooklyn and Queens sit on the western end of Long Island. The southern edge of that island, starting in Brooklyn and extending far beyond the city limits toward the El Dorado of the Hamptons, is strung with Atlantic beaches. Within the city’s bounds are Coney Island Beach, Brighton Beach, Manhattan Beach (which is in Brooklyn), Breezy Point, Jacob Riis Park, and Rockaway Beach (Far Rockaway, too). And not far past the city line are Long Beach and maybe the best of them all, Jones Beach, where, to a small boy 60 years ago, the sand seemed cleanest and the waves tallest, and where a vast, glistening pool with deck and diving boards was a refuge from the roughneck ­ocean.

Twentieth-­century photos of some of those beaches show ­subway-­car crowds, and generally suggest a golden age of beachgoing from the 1920s to the 1960s. My memories from the years around the end of World War II are of great stretches of sandy shore—“great” to a child being a very flexible ­measure—­with no room for a single additional blanket. Where did all these people come from? Surrounded, minimized, overlooked, I learned on a New York City ­beach—­probably on a ­Sunday—­that I was not the center of the universe after ­all.

The beach was a schoolroom before I knew what a schoolroom was. There I learned socialization (“Why don’t you go and play with that little boy over there?”), and skills that would come in handy in later life (“Why are you crying?” “He said he doesn’t want to be my friend anymore. So I smashed his truck.”)

I learned independence. I would go alone with pail and shovel to the water’s edge, where the sand was wettest and pocked with small, scaly creatures. I was perhaps 50 feet from my parents, having sworn to them to go no farther and having marked the location of their umbrella by color and angle and position along the line of lampposts on the boardwalk in the distance. I would dig for 10 minutes, though bored after two, then decide to return to home base. But ­uh-­oh, the landscape had shifted. Someone had moved the umbrellas, or maybe the boardwalk, because nothing was where it had been. Then a mother more caring than my own, who should never have let me go in the first place, would read the message on my alternately pinched and tremulous face: “Are you lost?” And riding some maternal broadcast frequency, the surrogate mother would home in on my ­own.

And I learned shame. Near the end of the day, like others of my age up and down the beach, I heard a variant of the same threat: “You’re not sitting in the car in those wet trunks. Do you want a rash?” So we were ordered to stand on blankets and hold towels round our waists. Our trunks were yanked down, we were patted to aridity with the towels, and clean underwear was yanked up. Never soon enough. But sometimes a kid would wriggle free of a parent during the drying phase and dance, jump, hop, and ­yell—­naked! “That’s stupid,” I would think, taking refuge in the catchall critical adjective that for a ­five-­year-­old expresses, inter alia, confusion, disgust, exasperation, and dismay. I was just too young to recognize a future celebrity in the ­making.

A dozen or so years later, I began to visit a beach that had been carved from several hundred feet of woods on a shore of Lake Champlain in upstate New York, not far from the Canadian border. The beach was on the property of a former resort hotel, and an old brochure boasted that the exceptionally fine white sand had been brought from Florida. It was “singing sand,” said the brochure, and if you put your ear to a small mound as it settled and ran, you would hear its song. Thanks to the brochure’s encouragement, many swore that they did, though no two ever described the same sweet ­susurrus.

A white wooden boardwalk and row of cabanas had once run the length of the beach, on either side of a central, ­pennant-­flying picnic pavilion. But by the time I knew the beach, the boardwalk and cabanas were no longer maintained, and, year by year, the ­one-­two punch of glacial northern winters and surprisingly full-bore summers had taken a toll on the wooden structures and felled another section. The huge lake lapping the beach froze solid each winter, to a depth that allowed cars to be driven on portions of its ­steely-­smooth surface in the perfect gray stillness before ­snow.

That snow inevitably covered the beach as well, and come spring, when the snow left, more of the virtuosic sand had left too, or had had its purity diminished by a new admixture of ordinary dirt. The sand went a little more offkey; left ungroomed, it would eventually go mute. Lying on that anomalous swath of shore late one spring, reading T. S. Eliot for a term paper (in those days the poet was at the height of his regard), I came to the passage that promises to show a reader fear in a handful of dust. Such is the risk in sunlit reverie that I wondered what the poet would have made of a handful of our singing sand. Would it have sung to him? Would he have walked on it with his trousers rolled? Would those vocal granules, displaced from their natural home, have told him that by no means is our end always in our ­beginning?

Of course, not every sunlit beach is conducive to reverie. A couple of decades later still, I stood on the deck of a house overlooking a beach south of Los Angeles that appeared to enforce an age restriction: Be under 35 or be gone—and start having second thoughts at 32. The area was probably posted for dreaming. Between the deck and the start of the beach, which extended hundreds of feet to the ocean, was a large expanse of paved surface, and on it a nonstop cavalcade of joggers, power walkers, cyclists, rollerbladers, and skateboarders, each cohort in its delineated row, passed in a spandexed blur. Beyond them, on the beach itself, teams of volleyballers jumped, lunged, and fell, and past the volleyballers, in the distant ocean, kayakers struggled and surfers bobbed, rose, and tumbled. (But for the sand and ocean, I might have been in Boulder, an immortalitarian stronghold, where to be still is grounds for deportation.) You’d have needed Hieronymus Bosch to put this California scene on a canvas, and even he might have been flummoxed by the ranks of busy figures to the ­horizon.

In another decade, I was thigh deep and thought free in the placid waters off a gulf coast Florida beach, when I noticed just ahead of me in the shallows first one fin and then a second, attached to what were plainly not porpoises. The two circling sand sharks, perhaps five feet long, were not ­man-­eaters, but maybe man-samplers, and certainly ­man-­bruisers. A hundred feet to my left was a stretch of water filled with dozens of adults and children. I walked to the closest couple of parents watching the kids. “I don’t mean to alarm you, but I just saw two sharks right over there. Maybe you should get the kids out. . . .” “Where?!” “Right there.” “Hey kids! Sharks! Over here!” And in the best ­moth-­to-­flame, ­floatie-­to-­fin, limb-to-jaw tradition, the curious families laughed and splashed their way toward an additional holiday ­memory.

Recently I returned to that same gulf beach, on a perfect May Sunday. I watched a group of teenagers, male and female, all ­more-­or-­less 16, begin to gather in early afternoon some 75 feet from where I sat. An initial six spread two blankets, and they were joined in leisurely course by more than a dozen others with blankets of their own. The patchwork encampment grew by the hour and took its mood from the raucous music of a boom box set atop a ­sky-­blue Styrofoam cooler. Unable to hear more of their talk than the occasional stray phrase or squeal, I invented a history for the group. They were school friends, I decided, or at least school acquaintances, who had suspended for the afternoon the narrow alliances by which they lived during the week in favor of a weekend ­UN-­ish coalition of the willing and ­frisky.

A minimalist aesthetic dictated the girls’ attire, which was scarce as the day’s clouds, while a preference for maritime ­hip-­hop dressed the boys in slack baggy trunks to below the knee. Boys ran into the water and returned to shake their wet bodies above recumbent, unaware girls, who were perfectly, gratefully aware. Lithe forms, male and female, lay prone and supine in calibrated proximity, stirring occasionally for the ­oh-­so-­matter-­of-­fact mutual application of a suntan product. The concentration of hormones dancing above the site reduced visibility to ­zero.

Then the boys advanced to the water to put on a show for the girls. To strut. To skim. But not on ­surfboards—­wrong coast of Florida for that. No, the small, brightly colored boards the boys carried merely slid along the surface of the wavelets at the gulf’s edge. After gauging the force and direction of the ripples as painstakingly as a golfer judging a showdown putt, a boy would sprint a short distance along the shore, throw down his board, jump on, and be carried a car’s length. Or not. Most attempts ended in disaster, an opportunity to fall one way onto the sand and roll a bit, or the other into the shallow water and make a sprawled-arms splash. The girls sat upright on the grandstand blankets, cheering or razzing their champions. While awaiting their turns at a run, boys wrestled one another or did handstands, and the sunshine behind them, bouncing from the water, turned them momentarily dark against the light. They were all exultant, eternal, ­oblivious.

And the reverie began. Looking up and down the beach, I could see who many of them would become: ­large—­way too ­large—­adults, variously tattooed, their handstand days long past, their bikinis tucked under yearbooks in a drawer. They would become parents, like those responsible folks down there close to the water, with the little kids and an assortment of pails. And soon enough they’d be middle aged, like those couples up near the dunes with no kids but with hats and an assortment of newspapers. And fast as a wave recedes they’d be old, like, well, like someone with a mind vagrant and addled, and sometimes bleached blank by too long a stay in the ­sun.