The Edge of the Sea

IV. The Rim of Sand

ON THE SANDS of the sea’s edge, especially where they are broad and bordered by unbroken lines of wind-built dunes, there is a sense of antiquity that is missing from the young rock coast of New England. It is in part a sense of the unhurried deliberation of earth processes that move with infinite leisure, with all eternity at their disposal. For unlike that sudden coming in of the sea to flood the valleys and surge against the mountain crests of the drowned lands of New England, the sea and the land lie here in a relation established gradually, over millions of years.

During those long ages of geologic time, the sea has ebbed and flowed over the great Atlantic coastal plain. It has crept toward the distant Appalachians, paused for a time, then slowly receded, sometimes far into its basin; and on each such advance it has rained down its sediments and left the fossils of its creatures over that vast and level plain. And so the particular place of its stand today is of little moment in the history of the earth or in the nature of the beach—a hundred feet higher, or a hundred feet lower, the seas would still rise and fall unhurried over shining flats of sand, as they do today.

And the materials of the beach are themselves steeped in antiquity. Sand is a substance that is beautiful, mysterious, and infinitely variable; each grain on a beach is the result of processes that go back into the shadowy beginnings of life, or of the earth itself.

The bulk of seashore sand is derived from the weathering and decay of rocks, transported from their place of origin to the sea by the rains and the rivers. In the unhurried processes of erosion, in the freighting seaward, ±n the interruptions and resumptions of that journey, the minerals have suffered various fates—some have been dropped, some have worn out and vanished. In the mountains the slow decay and disintegration of the rocks proceed, and the stream of sediments grows—suddenly and dramatically by rockslides—slowly, inexorably, by the wearing of rock by water. All begin their passage toward the sea. Some disappear through the solvent action of water or by grinding attrition in the rapids of a river’s bed. Some are dropped on the riverbank by flood waters, there to lie for a hundred, a thousand years, to become locked in the sediments of the plain and wait another million years or so, during which, perhaps, the sea comes in and then returns to its basin. Then at last they are released by the persistent work of erosion’s tools-wind, rain, and frost—to resume the journey to the sea. Once brought to salt water, a fresh rearranging, sorting, and transport begin. Light minerals, like flakes of mica, are carried away almost at once; heavy ones like the black sands of ilmenite and rutile are picked up by the violence of storm waves and thrown on the upper beach.

No individual sand grain remains long in any one place. The smaller it is, the more it is subject to long transport—the larger grains by water, the smaller by wind. An average grain of sand is only two and one half times the weight of an equal volume of water, but more than two thousand times as heavy as air, so only the smaller grains are available for transport by wind. But despite the constant working over of the sands by wind and water, a beach shows little visible change from day to day, for as one grain is carried away, another is usually brought to take its place.

The greater part of most beach sand consists of quartz, the most abundant of all minerals, found in almost every type of rock. But many other minerals occur among its crystal grains, and one small sample of sand might contain fragments of a dozen or more. Through the sorting action of wind, water, and gravity, fragments of darker, heavier minerals may form patches overlying the pale quartz. So there may be a curious purple shading over the sand, shifting with the wind, piling up in little ridges of deeper color like the ripple marks of waves—a concentration of almost pure garnet. Or there may be patches of dark green—sands formed of glauconite, a product of the sea’s chemistry and the interaction of the living and the non-living. Glauconite is a form of iron silicate that contains potassium; it has occurred in the deposits of all geologic ages. According to one theory, it is forming now in warm shallow areas of the sea’s floor, where the shells of minute creatures called foraminifera are accumulating and disintegrating on muddy sea bottoms. On many Hawaiian beaches, the somber darkness of the earth’s interior is reflected in sand grains of olivine derived from black basaltic lavas. And drifts of the “black sands” of rutile and ilmenite and other heavy minerals darken the beaches of Georgia’s St. Simons and Sapelo Islands, clearly separated from the lighter quartz.

In some parts of the world the sands represent the remains of plants that in life had lime-hardened tissues, or fragments of the calcareous shells of sea creatures. Here and there on the coast of Scotland, for example, are beaches composed of glistening white “nullipore sands”—the shattered and sea-ground remains of coralline algae growing on the bottom offshore. On the coast of Galway in Ireland the dunes are built of sands composed of tiny perforated globes of calcium carbonate—the shells of foraminifera that once floated in the sea. The animals were mortal but the shells they built have endured. They drifted to the floor of the sea and became compacted into sediment. Later the sediments were uplifted to form cliffs, which were eroded and returned once more to the sea. The shells of foraminifera appear also in the sands of southern Florida and the Keys, along with coral debris and the shells of mollusks, shattered, ground, and polished by the waves.

From Eastport to Key West, the sands of the American Atlantic coast, by their changing nature, reveal a varied origin. Toward the northern part of the coast mineral sands predominate, for the waves are still sorting and rearranging and carrying from place to place the fragments of rock that the glaciers brought down from the north, thousands of years ago. Every grain of sand on a New England beach has a long and eventful history. Before it was sand, it was rock—splintered by the chisels of the frost, crushed under advancing glaciers and carried forward with the ice in its slow advance, then ground and polished in the mill of the surf. And long ages before the advance of the ice, some of the rock had come up into the light of the sun from the black interior of the earth by ways unseen and for the most part unknown, made fluid by subterranean fires and rising along deep pipes and fissures. Now in this particular moment of its history, it belongs to the sea’s edge—swept up and down the beaches with the tides or drifted alongshore with the currents, continuously sifted and sorted, packed down, washed out, or set adrift again, as always and endlessly the waves work over the sands.

On Long Island, where much glacial material has accumulated, the sands contain quantities of pink and red garnet and black tourmaline, along with many grains of magnetite. In New Jersey, where the coastal plain deposits of the south first appear, there is less magnetic material and less garnet. Smoky quartz predominates at Barnegat, glauconite at Monmouth Beach, and heavy minerals at Cape May. Here and there beryl occurs where molten magma has brought up deeply buried material of the ancient earth to crystallize near the surface.

North of Virginia, less than half of one per cent of the sands are of calcium carbonate; southward, about 5 per cent. In North Carolina the abundance of calcareous or shell sand suddenly increases, although quartz sand still forms the bulk of the beach materials. Between Capes Hatteras and Lookout as much as 10 per cent of the beach sand is calcareous. And in North Carolina also there are odd local accumulations of special materials such as silicified wood—the same substance that is contained in the famous “singing sands” of the Island of Eigg in the Hebrides.

The mineral sands of Florida are not of local origin but have been derived from the weathering of rocks in the Piedmont and Appalachian highlands of Georgia and South Carolina. The fragments are carried to the sea on southward-moving streams and rivers. Beaches of the northern part of Florida’s Gulf Coast are almost pure quartz, composed of crystal grains that have descended from the mountains to sea level, accumulating there in plains of snowlike whiteness. About Venice there is a special sparkle and glitter over the sands, where crystals of the mineral zircon are dusted over its surface like diamonds; and here and there is a sprinkling of the blue, glasslike grains of cyanite. On the east coast of Florida, quartz sands predominate for much of the long coast line (it is the hard-packing quartz grains that compose the famous beaches of Daytona) but toward the south, the crystal sands are mingled more and more with fragments of shells. Near Miami the beach sands are less than half quartz; about Cape Sable and in the Keys the sand is almost entirely derived from coral and shell and the remains of foraminifera. And all along the east coast of Florida, the beaches receive small contributions of volcanic matter, as bits of floating pumice that have drifted for thousands of miles in ocean currents are stranded on the shore to become sand.

Infinitely small though it is, something of its history may be revealed in the shape and texture of a grain of sand. Wind-transported sands tend to be better rounded than water-borne; furthermore, their surface shows a frosted effect from the abrasion of other grains carried in the blast of air. The same effect is seen on panes of glass near the sea, or on old bottles in the beach flotsam. Ancient sand grains, by their surface etchings, may give a clue to the climate of past ages. In European deposits of Pleistocene sand, the grains have frosted surfaces etched by the great winds blowing off the glaciers of the Ice Age.

We think of rock as a symbol of durability, yet even the hardest rock shatters and wears away when attacked by rain, frost or surf. But a grain of sand is almost indestructible. It is the ultimate product of the work of the waves—the minute, hard core of mineral that remains after years of grinding and polishing. The tiny grains of wet sand lie with little space between them, each holding a film of water about itself by capillary attraction. Because of this cushioning liquid film, there is little further wearing by attrition. Even the blows of heavy surf cannot cause one sand grain to rub against another.

In the intertidal zone, this minuscule world of the sand grains is also the world of inconceivably minute beings, which swim through the liquid film around a grain of sand as fish would swim through the ocean covering the sphere of the earth. Among this fauna and flora of the capillary water are single-celled animals and plants, water mites, shrimplike crustacea, insects, and the larvae of certain infinitely small worms—all living, dying, swimming, feeding, breathing, reproducing in a world so small that our human senses cannot grasp its scale, a world in which the micro-droplet of water separating one grain of sand from another is like a vast, dark sea.

Not all sands are inhabited by this “interstitial fauna.” Those derived from the weathering of crystalline rocks are most abundantly populated. Shell or coral sand seldom if ever contains copepods and other microscopic life; perhaps this indicates that the grains of calcium carbonate create unfavorably alkaline conditions in the water around them.

On any beach the sum of all the little pools amid the sand grains represents the amount of water available to the animals of the sands during the low-tide interval. Sand of average fineness is able to contain almost its own volume of water, and so at low tide only the topmost layers dry out under a warm sun. Below it is damp and cool, for the contained water keeps the temperatures of the deeper sand practically constant. Even the salinity is fairly stable; only the most superficial layers are affected by rain falling on the beach or by streams of fresh water coursing across it.

Bearing on its surface only the wave-carved ripple marks, the fine traceries of sand grains dropped at last by the spent waves, and the scattered shells of long-dead mollusks, the beach has a lifeless look, as though not only uninhabited but indeed uninhabitable. In the sands almost all is hidden. The only clues to the inhabitants of most beaches are found in winding tracks, in slight movements disturbing the upper layers, or in barely protruding tubes and all but concealed openings leading down to hidden burrows.

The signs of living creatures are often visible, if not the animals themselves, in deep gullies that cut the beaches, parallel to the shore line, and hold at least a few inches of water from the fall of one tide until the return of the next. A little moving hill of sand may yield a moon snail intent on predatory errand. A V-shaped track may indicate the presence of a burrowing clam, a sea mouse, a heart urchin. A flat ribbonlike track may lead to a buried sand dollar or a starfish. And wherever protected flats of sand or sandy mud lie exposed between the tides, they are apt to be riddled with hundreds of holes, marked by the sign of the ghost shrimps within. Other flats may bristle with forests of protruding tubes, pencil thin and decorated weirdly with bits of shell or seaweed, an indication that legions of the plumed worm, Diopatra, live below. Or again there may be a wide area marked by the black conical mounds of the lugworm. Or here at the edge of the tide a chain of little parchment capsules, one end free and the other disappearing under the sand, shows that one of the large predatory whelks lies below, busy with the prolonged task of laying and protecting her eggs.

But almost always the essence of the lives—the finding of food, the hiding from enemies, the capturing of prey, the producing of young, all that makes up the living and dying and perpetuating of this sand-beach fauna—is concealed from the eyes of those who merely glance at the surface of the sands and declare them barren.

I remember a chill December morning on one of Florida’s Ten Thousand Islands, with the sands wet from a recently fallen tide and the fresh, clean wind blowing handfuls of spindrift along the beach. For several hundred yards, where the shore ran in a long curve from the Gulf toward the shelter of the bay, there were peculiar markings on the dark wet sand just above the water’s edge. The marks were arranged in groups, in each of which a series of thin spidery lines radiated out from a central spot, as though unsteadily traced there by a slender stick. At first no sign of any living animal was to be seen—nothing to tell what creature had made these seemingly careless scribblings. After kneeling on the wet sand and looking at one after another of these strange insignia, I found that under each of the central spots lay the flat pentagonal disc of a serpent starfish. The marks on the sand were made by its long and slender arms, inscribing the record of its forward progress.

And then I remember wading on a June day over Bird Shoal, which lies off the town of Beaufort in North Carolina, where at low tide acres of sand bottom are covered only by a few inches of water. Near the shore I found two sharply defined grooves in the sand; my index finger could have measured their span. Between the grooves was a faint, irregular line. Step by step, I was led out across the flat by the tracks; finally, at the temporary end of the trail, I came upon a young horseshoe crab, heading seaward.

For most of the fauna of the sand beaches, the key to survival is to burrow into the wet sand, and to possess means of feeding, breathing and reproducing while lying below reach of the surf. And so the story of the sand is in part the story of small lives lived deep within it, finding in its dark, damp coolness a retreat from fish that come hunting with the tide and from birds that forage at the water’s edge when the tide has fallen. Once below the surface layers, the burrower has found not only stable conditions but also a refuge where few enemies threaten. Those few are likely to reach down from above—perhaps a bird thrusting a long bill into the hole of a fiddler crab—a sting ray flapping along the bottom, plowing up the sand for buried mollusks—an octopus sliding an exploring tentacle down into a hole. Only an occasional enemy comes through the sand. The moon snail is a predator that makes a successful living in this difficult way. It is a blind creature with no use for eyes because it is forever groping through dark sands, hunting mollusks that live as much as a foot below the surface. Its smoothly rounded shell eases its descent into the sand as it digs with the immense foot. On locating prey, it holds the animal with the foot and drills a round hole in the shell. The moon snails are voracious; young animals eat more than a third of their weight in clams each week. Some worms also are predatory burrowers; so are a few starfish. But for most predators, continuous burrowing consumes more energy than would be supplied by the prey thus found. Most of the burrowers in sand are passive feeders, digging only enough to establish a temporary or permanent home in which to lie while straining food from the water or sucking up detritus that accumulates on the sea bottom.

The rising tide sets in action a system of living filters through which prodigious quantities of water are strained. Buried mollusks push up their siphons through the sand to draw the incoming water through their bodies. Worms lying in U-shaped parchment tubes begin to pump, drawing the water in through one end of the tube, expelling it through the other. The incoming stream brings food and oxygen; the outgoing has been depleted of much of the food and bears away the organic wastes of the worm. Small crabs spread the feathery nets of their antennae like cast-nets to bring in food.

With the tide, predators come from offshore. A blue crab dashes out of the surf to seize a fat mole crab that is in the act of spreading its antennae to filter the backwash of a receding wave. Clouds of salt-water minnows move in with the tide, searching for the small amphipods of the upper beach. Launce, or sand eels, dart through the shallow water seeking copepods or fish fry; sometimes the launce are pursued by the shadowy forms of larger fish.

As the tide falls much of this extraordinary activity slackens. There is less eating and being eaten. In the wet sands, however, some animals can continue to eat even after the tide has receded. Lugworms can continue their work of passing sand through their bodies for the sake of the scraps of nutriment they contain. Heart urchins and sand dollars, lying in saturated sand, continue to sort out bits of food. But over most of the sands there is a lull of repletion—of waiting for the turn of the tide.

Although there are many places where, on quieter shores and protected shoals, such richness of life may be found, certain ones live most clearly in my memories. On one of the sea islands of Georgia is a great beach that is visited only by the most gentle surf, although it looks straight across to Africa. Storms usually pass it by, for it lies well inside the long, incurving arc of coast that swings between the Capes of Fear and Canaveral, and the prevailing winds are such that no heavy swells roll in upon it. The texture of the beach itself is unusually firm because of a mixture of mud and clay with the sand; permanent holes and burrows can be dug in it, and the streaming tidal currents carve little ripple marks that remain after the tide goes out, looking like a miniature model of the sea’s waves. These sand ripples hold small food particles dropped by the currents, providing a store to be drawn on by detritus feeders. The slope of the beach is so gentle that, when the tide falls to its lowest ebb, a quarter of a mile of sand is exposed between the high-tide line and the low. But this broad sand flat is not a perfectly even plain, for winding gullies wander across it, like creeks across the land, holding a remnant of water from the last high tide and providing a living place for animals that cannot endure even a temporary withdrawal of the water.

It was in this place that I once found a large “bed” of sea pansies at the very edge of the tide. The day was heavily overcast, a fact that accounted for their being exposed. On sunny days I never saw them there, although undoubtedly they were just under the sand, protecting themselves from the drying rays of the sun.

But the day I saw them the pink and lavender flower faces were lifted so that they were exposed at the surface of the sand, though so slightly that one could easily pass them by unnoticed. Seeing them—even recognizing them for what they were—there was a sense of incongruity in finding what looked so definitely flowerlike here at the edge of the sea.

These flattened, heart-shaped sea pansies, raised on short stems above the sand, are not plants but animals. They belong to the same general group of simple beings as the jellyfish, sea anemones, and corals, but to find their nearest relatives one would have to desert the shore and go down to some deeplying offshore bottom where, as fernlike growths in a strange animal forest, the sea pens thrust long stalks into the soft ooze.

Each sea pansy growing here at the edge of the tide is the product of a minute larva that once dropped from the currents to this shore. But through the extraordinary course of its development it has ceased to be that single being of its origin and has become instead a group or colony of many individuals, bound together into a whole of flowerlike form. The various individuals or polyps all have the shape of little tubes embedded in the fleshy substance of the colony. But some of the tubes bear tentacles and look like very small sea anemones; these capture food for the colony, and in the proper season form reproductive cells. Other tubes lack tentacles; these are the engineers of the colony, attending to the functions of water-intake and control. A hydraulic system of changing water pressure controls the movements of the colony; as the stem is made turgid it may be thrust down into the sand, drawing the main body after it.

As the rising tide streams over the flattened shapes of the sea pansies, all the tentacles of the feeding polyps are thrust up, reaching for the living motes that dance in the water—the copepods, the diatoms, the fish larvae small and tenuous as threads.

And at night the shallow water, rippling gently over these flats, must glow softly with hundreds of little lights marking out the zone where the sea pansies live, in a serpentine line of gleaming points, just as lights seen from an airplane at night wander across the dark landscape and show the path of settlement along a highway. For the sea pansies, like their deep-sea relatives, are beautifully luminescent.

In season, the tide sweeping over these flats carries many small, pear-shaped, swimming larvae from which new colonies of pansies will develop. In past ages, the currents that traversed the open water then separating North and South America carried such larvae, which established themselves on the Pacific coast, north to Mexico and south to Chile. Then a bridge of land rose between the American continents, closing the water highway. Today the presence of sea pansies on both Atlantic and Pacific coasts is one of the living reminders of that past geologic time when North and South America were separated, and sea creatures passed freely from one ocean to the other.

In that liquescent sand at the edge of the low tide, I often saw small bubblings and boilings under the surface as one or another of the sand dwellers slipped in or out of its hidden world.

There were sand dollars, or keyhole urchins, thin as wafers. As one of them buried itself the forward edge slipped obliquely into the sand, passing with effortless ease from the world of sunlight and water into those dim regions of which my senses knew nothing. Internally, the shells are strengthened for burrowing, and against the force of surf, by supporting pillars that occupy most of the region between upper and lower shells except in the center of the disc. The surface of the animal is covered with minute spines, soft as felt. The spines shimmered in the sunlight as their waving movements set up currents that kept the sand grains in motion and eased the passage of the creature from water into earth. On the back of the disc was dimly marked out a design like a five-petaled flower. Repeating the meaning and the symbolism of the number five—the sign of the echinoderms—were five holes perforating the flat disc. As the animal progressed just under the shifting film of surface sand, grains moved up from the under side through the holes, aiding its forward movement and spreading a concealing veil of sand over its body.

The sand dollars shared their dark world with other echinoderms. Down in the wet sand lived heart urchins, which one never sees at the surface until the thin little boxes that once contained them are found by the tide and carried in to the beach, to be blown about by the wind and left at last in the litter of the high-tide line. The oddly shaped heart urchins lay in chambers six inches or more below the surface of the sand, keeping open for themselves channels lined with sticky mucus; through these they reached up to the floor of the shallow sea, finding diatoms and other particles of food among the sand grains.

And sometimes a starlike pattern twinkled in that firmament of sand, proclaiming that one of the sand-dwelling starfishes lay below, marking out its image by the flow of water currents, as the animal drew sea water through its body for respiration, expelling it through many pores on its upper surface. If the sand was disturbed, the astral image trembled and faded, like a star disappearing in mist, as the animal glided away rapidly, paddling through the sand with flattened tube feet.

Walking back across the flats of that Georgia beach, I was always aware that I was treading on the thin rooftops of an underground city. Of the inhabitants themselves little or nothing was visible. There were the chimneys and stacks and ventilating pipes of underground dwellings, and various passages and runways leading down into darkness. There were little heaps of refuse that had been brought up to the surface as though in an attempt at some sort of civic sanitation. But the inhabitants remained hidden, dwelling silently in their dark, incomprehensible world.

The most numerous inhabitants of this city of burrowers were the ghost shrimps. Their holes were everywhere over the tidal flat, in diameter considerably smaller than a lead pencil, and surrounded by a little pile of fecal pellets. The pellets accumulate in great quantity because of the shrimp’s way of life; it must eat an enormous amount of sand and mud to obtain the food that is mixed with this indigestible material. The holes are the visible entrances to burrows that extend down several feet into the sand—long, nearly vertical passageways from which other tunnels lead off, some continuing down into the dark, damp basement of this shrimp city, others leading up to the surface as though to provide emergency exit doors.

The owners of the burrows did not show themselves unless I tricked them into it by dropping sand grains, a few at a time, into their entrance halls. The ghost shrimp is a curiously formed creature with a long slender body. It seldom goes abroad and so has no need of a hard protective skeleton; it is covered, instead, with a flexible cuticle suited to the narrow tunnel in which it must be able to dig and turn about. On the under side of its body are several pairs of flattened appendages that beat continually to force a current of water through the burrow, for in the deep sand layers the oxygen supply is poor, and aerated water must be drawn down from above. When the tide comes in, the ghost shrimps go up to the mouths of their burrows and begin their work of sifting the sand grains for bacteria, diatoms, and perhaps larger particles of organic detritus. The food is brushed out of the sand by means of little hairs on several of the appendages, and is then transferred to the mouth.

Few of those who build permanent homes in this underground city of sand live by themselves. On the Atlantic coast, the ghost shrimp regularly gives lodging to a small rotund crab, related to the species often found in oysters. The pea crab, Pinnixa, finds in the well-aerated burrow of the shrimp both shelter and a steady supply of food. It strains food out of the water currents that flow through the burrow, using little feathery outgrowths of its body as nets. On the California coast the ghost shrimp shelters as many as ten different species of animals. One is a fish—a small goby—that uses the burrow as a casual refuge while the tide is out, roaming through the passageways of the shrimp’s home and pushing past the owner when necessary. Another is a clam that lives outside the burrow but thrusts its siphons through the walls and takes food from the water circulating through the tunnel. The clam has short siphons and in ordinary circumstances would have to live just under the surface of the sand to reach water and its food supply; by establishing connection with the shrimp’s burrow it is able to enjoy the protective advantages of living at a deeper level.

On the muddier parts of these same Georgia flats the lugworm lives, its presence marked by round black domes, like low volcanic cones. Wherever the lugworms occur, on shores of America and Europe, their prodigious toil leavens and renews the beaches and keeps the amount of decaying organic matter in proper balance. Where they are abundant, they may work over in a year nearly two thousand tons of soil per acre. Like its counterpart on land, the earthworm, the lugworm passes quantities of soil through its body. The food in decaying organic debris is absorbed by its digestive tract; the sand is expelled in neat, coiled castings that betray the presence of the worm. Near every dark cone, a small, funnel-shaped depression appears in the sand. The worm lies within the sand in the shape of the letter U, the tail under the cone, the head under the depression. When the tide rises, the head is thrust out to feed.

Other signs of the lugworm appear in midsummer—large, translucent, pink sacs, each bobbing about in the water like a child’s balloon, with one end drawn down into the sand. These compact masses of jelly are the egg masses of the worm, within each of which as many as 300,000 young are undergoing development.

Vast plains of sand are continually worked over by these and other marine worms. One—the trumpet worm—uses the very sand that contains its food to make a cone-shaped tube for the protection of its soft body in tunneling. One may sometimes see the living trumpet worm at work, for it allows its tube to project slightly above the surface. It is much more common, however, to find the empty tubes in the tidal debris. Despite their fragile appearance, they remain intact long after their architects are dead—natural mosaics of sand, one grain thick, the building stones fitted together with meticulous care.

A Scot named A. T. Watson once spent many years studying the habits of this worm. Because tube-building goes on under ground, he found it almost impossibly difficult to observe the fitting into place and cementing of sand grains until he hit upon the idea of collecting very young larvae, which could live and be observed in a thin layer of sand in the bottom of a laboratory dish. The building of the tube was begun soon after the larvae had ceased to swim about and had settled on the bottom of the dish. First each secreted a membranous tube about itself. This was to become the inner lining of the cone, and the foundation for the sand-grain mosaic. These young larvae had only two tentacles, which they used to collect grains of sand and pass them to the mouth. There the grains were rolled about experimentally, and if found suitable, were deposited on the chosen spot at the edge of the tube. Then a little fluid was expelled from the cement gland, after which the worm rubbed certain shield-like structures over the tube as though to smooth it.

“Each tube,” wrote Watson, “is the life work of the tenant, and is most beautifully built with grains of sand, each grain placed in position with all the skill and accuracy of a human builder … The moment when an exact fit has been obtained is evidently ascertained by an exquisite sense of touch. On one occasion I saw the worm slightly alter (before cementing) the position of a sand grain which it had just deposited.”

The tubes serve to house the owners during a lifetime of subterranean tunneling, for like the lugworm, this species finds its food in the subsurface sands. The digging organs, like the tubes, belie their fragile appearance. They are slender, sharp-pointed bristles arranged in two groups, or “combs,” which look fantastically impractical. We could easily believe that someone, in whimsical mood, had cut them out of shining golden foil, fringing the margins with repeated snips of the scissors to fashion a Christmas tree ornament.

I have watched the worms at work, in a miniature world of sand and sea created for them in my laboratory. Even in a thin layer of sand in a glass bowl, the combs are used with a sturdy efficiency that reminds one of a bulldozer. The worm emerges slightly from the tube, thrusts the combs into the sand, scoops up a load and throws it over its shoulder, as it were; than it seems to scrape the shovel blades clean by drawing them back over the edge of the tube. The whole thing is done with vigor and dispatch, with motions alternately to right and left. The golden shovels loosen the sand and allow the soft, food-gathering tentacles to explore among the grains, and bring to the mouth the food they discover.

Down along the line of barrier islands that stands between the mainland and the sea, the waves have cut inlets through which the tides pour into the bays and sounds behind the islands. The seaward shores of the islands are bathed by coastwise currents carrying their loads of sand and silt, mile after mile. In the confusion of meeting the tides that are racing to or from the inlets, the currents slacken and relax their hold on some of the sediments. So, off the mouths of many of the inlets, lines of shoals make out to sea—the wrecking sands of Diamond Shoal and Frying Pan Shoal and scores of others, named or nameless. But not all of the sediments are so deposited. Many are seized by the tides and swept through the inlets, only to be dropped in the quieter waters inside. Within the capes and the inlet mouths, in the bays and sounds, the shoals build up. Where they exist the searching larvae or young of sea creatures find them—creatures whose way of life requires quiet and shallow water.

Within the shelter of Cape Lookout there are such shoals reaching upward to the surface, emerging briefly into sun and air for the interval of the low tide, then sinking again into the sea. They are seldom crossed by heavy surf, and while the tidal currents that swirl over or around them may gradually alter their shape and extent—today borrowing some of their substance, tomorrow repaying it with sand or silt brought from other areas—they are on the whole a stable and peaceful world for the animals of the sands.

Some of the shoals bear the names of the creatures of air and water that visit them—Shark, Sheepshead, Bird. To visit Bird Shoal, one goes out by boat through channels winding through the Town Marsh of Beaufort and comes ashore on a rim of sand held firm by the deep roots of beach grasses—the landward border of the shoal. The burrows of thousands of fiddler crabs riddle the muddy beach on the side facing the marshes. The crabs shuffle across the flats at the approach of an intruder, and the sound of many small chitinous feet is like the crackling of paper. Crossing the ridge of sand, one looks out over the shoal. If the tide still has an hour or two to fall to its ebb, one sees only a sheet of water shimmering in the sun.

On the beach, as the tide falls, the border of wet sand gradually retreats toward the sea. Offshore, a dull velvet patch takes form on the shining silk of the water, like the back of an immense fish slowly rolling out of the sea, as a long streak of sand begins to rise into view.

On spring tides the peak of this great sprawling shoal rises farther out of the water and is exposed longer; on the neaps, when the tidal pulse is feeble and the water movements sluggish, the shoal remains almost hidden, with a thin sheet of water rippling across it even at the low point of the ebb. But on any low tide of the month, in calm weather, one is able to wade out from the sand-dune rim over immense areas of the shoal, in water so shallow and so glassy clear that every detail of the bottom lies revealed.

Even on moderate tides I have gone so far out that the dry sand rim seemed far away. Then deep channels began to cut across the outlying parts of the shoal. Approaching them, I could see the bottom sloping down out of crystal clarity into a green that was dull and opaque. The steepness of the slope was accentuated when a little school of minnows flickered across the shallows and down into the darkness in a cascade of silver sparks. Larger fish wandered in from the sea along these narrow passages between the shoals. I knew there were beds of sun ray clams down there on the deeper bottoms, with whelks moving down to prey on them. Crabs swam about or buried themselves to the eyes in the sandy bottoms; then behind each crab two small vortices appeared in the sand, marking the respiratory currents drawn in through the gills.

Where water—even the shallowest of layers—covered the shoal, life came out of hiding. A young horseshoe crab hurried out into deeper water; a small toadfish huddled down in a clump of eelgrass and croaked an audible protest at the foot of a strange visitor in his world, where human beings seldom intrude. A snail with neat black spirals around its shell and a matching black foot and black, tubular siphons—a banded tulip shell—glided rapidly over the bottom, tracing a clear track across the sand.

Here and there the sea grasses had taken hold—those pioneers among the flowering plants that are venturing out into salt water. Their flat leaf blades pushed up through the sand and their interlacing roots lent firmness and stability to the bottom. In such glades I found colonies of a curious, sand-dwelling sea anemone. Because of their structure and habits, anemones require some firm support to grip while reaching into the water for food. In the north (or wherever there is firm bottom) they grasp the rocks; here they gain the same end by pushing down into the sand until only the crown of tentacles remains above the surface. The sand anemone burrows by contracting the downward-pointing end of its tube and thrusting downward, then as a slow wave of expansion travels up the body, the creature sinks into the sand. It was strange to see the soft tentacle-clusters of the anemones flowering here in the midst of the sands, for anemones seem always to belong to the rocks; yet buried in this firm bottom doubtless they were as secure as the great plumose anemone blooming on the wall of a Maine tide pool.

Here and there over the grassy parts of the shoal the twin chimneys of the parchment worm’s tubes protruded slightly above the sand. The worm itself lives always underground, in a U-shaped tube whose narrowed tips are the animal’s means of contact with the sea. Lying in its tube, it uses fanlike projections of the body to keep a current of water streaming through the dark tunnel of its home, bringing it the minute plant cells that are its principal food, carrying away its waste products and in season the seeds of a new generation.

The whole life of the worm is so spent except for the short period of larval life at sea. The larva soon ceases to swim and, becoming sluggish, settles to the bottom. It begins to creep about, perhaps finding food in the diatoms lying in the troughs of the sand ripples. As it creeps it leaves a trail of mucus. After perhaps a few days the young worm begins to make short, mucus-coated tunnels, burrowing into thick clumps of diatoms mixed with sand. From such a simple tunnel, extending perhaps several times the length of its body, the larva pushes up extensions to the surface of the sand, to create the U-shape. All later tunnels are the result of repeated remodelings and extensions of this one, to accommodate the growing body of the worm. After the worm dies the limp, empty tubes are washed out of the sand and are common in the flotsam of the beach.

At some time almost all parchment worms acquire lodgers—the small pea crabs whose relatives inhabit the burrows of the ghost shrimps. Often the association is for life. The crabs, lured by the continuous stream of food-laden water, enter the worm tube while young, but soon become too large to leave by the narrow exits. Nor does the worm itself actually leave its tube, although occasionally one sees a specimen with a regenerated head or tail—mute evidence that it may emerge enough to tempt a passing fish or crab. Against such attacks it has no defense, unless the weird blue-white light that illuminates its whole body when disturbed may sometimes alarm an enemy.

Other little protruding chimneys raised above the surface of the shoal belonged to the plumed or decorator worm, Diopatra. These occurred singly, instead of in pairs. They were curiously adorned with bits of shell or seaweed that effectively deceived the human eye, and were but the exposed ends of tubes that sometimes extended down into the sand as much as three feet. Perhaps the camouflage is effective also against natural enemies, yet to collect the materials that it glues to all exposed parts of its tube, the worm has to expose several inches of its body. Like the parchment worm, it is able to regenerate lost tissues as a defense against hungry fish.

As the tide ebbed away, the great whelks could be seen here and there gliding about in search of their prey, the clams that lay buried in the sands, drawing through their bodies a stream of sea water and filtering from it microscopic plants. Yet the search of the whelks was not an aimless one, for their keen taste sense guided them to invisible streams of water pouring from the outlet siphons of the clams. Such a taste trail might lead to a stout razor clam, whose shells afford only the scantiest covering for its bulging flesh, or to a hard-shell clam, with tightly closed valves. Even these can be opened by a whelk, which grips the clam in its large foot and, by muscular contractions, delivers a series of hammer blows with its own massive shell.

Nor does the cycle of life—the intricate dependence of one species upon another—end there. Down in dark little dens of the sea floor live the enemies of the whelks, the stone crabs of massive purplish bodies and brightly colored crushing claws that are able to break away the whelk’s shell, piece by piece. The crabs lurk in caves among the stones of jetties, in holes eroded out of shell rock, or in man-made homes such as old, discarded automobile tires. About their lairs, as about the abodes of legendary giants, lie the broken remains of their prey.

If the whelks escape this enemy, another comes by air. The gulls visit the shoal in numbers. They have no great claws to crush the shells of their victims, but some inherited wisdom has taught them another device. Finding an exposed whelk, a gull seizes it and carries it aloft. It seeks a paved road, a pier, or even the beach itself, soars high into the air and drops its prey, instantly following it earthward to recover the treasure from among the shattered bits of shell.

Coming back over the shoal, I saw spiraling up out of the sand, over the edge of a green undersea ravine, a looped and twisted strand—a tough string of parchment on which were threaded many scores of little purse-shaped capsules. This was the egg string of a female whelk, for it was June, and the spawning time of the species. In all the capsules, I knew, the mysterious forces of creation were at work, making ready thousands of baby whelks, of which perhaps hundreds would survive to emerge from the thin round door in the wall of each capsule, each a tiny being in a miniature shell like that of its parents.

Where the waves roll in from the open Atlantic, with no outlying islands or curving arm of land to break the force of their attack on the beach, the area between the tide lines is a difficult one for living things. It is a world of force and change and constant motion, where even the sand acquires some of the fluidity of water. These exposed beaches have few inhabitants, for only the most specialized creatures can live on sand amid heavy surf.

Animals of open beaches are typically small, always swift-moving. Theirs is a strange way of life. Each wave breaking on the beach is at once their friend and enemy; though it brings food, it threatens to carry them out to sea in its swirling backwash. Only by becoming amazingly proficient in rapid and constant digging can any animal exploit the turbulent surf and shifting sand for the plentiful food supplies brought in by the waves.

One of the successful exploiters is the mole crab, a surf-fisher who uses nets so efficient that they catch even microorganisms adrift in the water. Whole cities of mole crabs live where the waves are breaking, following the flood tide shoreward, retreating toward the sea on the ebb. Several times during the rising of a tide, a whole bed of them will shift its position, digging in again farther up the beach in what is probably a more favorable depth for feeding. In this spectacular mass movement, the sand area suddenly seems to bubble, for in a strangely concerted action, like the flocking of birds or the schooling of fish, the crabs all emerge from the sand as a wave sweeps over them. In the rush of turbulent water they are carried up the beach; then, as the wave’s force slackens, they dig into the sand with magical ease, by means of a whirling motion of the tail appendages. With the ebbing of the tide, the crabs return toward the low-water mark, again making the journey in several stages. If by mischance a few linger until the tide has dropped below them, these crabs dig down several inches into the wet sand and wait for the return of the water.

As the name suggests, there is something mole-like in these small crustaceans, with their flattened, pawlike appendages. Their eyes are small and practically useless. Like all others who live within the sands the crabs depend less on sight than on the sense of touch, made wonderfully effective by the presence of many sensory bristles. But without the long, curling, feathery antennae, so efficiently constructed that even small bacteria become entangled in their strands, the mole crab could not survive as a fisher of the surf. In preparing to feed, the crab backs down into the wet sand until only the mouth parts and the antennae are exposed. Although it lies facing the ocean, it makes no attempt to take food from the incoming surf. Rather, it waits until a wave has spent its force on the beach and the backwash is draining seaward. When the spent wave has thinned to a depth of an inch or two, the mole crab extends its antennae into the streaming current. After “fishing” for a moment, it draws the antennae through the appendages surrounding its mouth, picking off the captured food. And again in this activity there is a curious display of group behavior, for when one crab thrusts up its antennae, all the others of the colony promptly follow its example.

It is an extraordinary thing to watch the sand come to life if one happens to be wading where there is a large colony of the crabs. One moment it may seem uninhabited. Then, in that fleeting instant when the water of a receding wave flows seaward like a thin stream of liquid glass, there are suddenly hundreds of little gnome-like faces peering through the sandy floor—beady-eyed, long-whiskered faces set in bodies so nearly the color of their background that they can barely be seen. And when, almost instantly, the faces fade back into invisibility, as though a host of strange little troglodytes had momentarily looked out through the curtains of their hidden world and as abruptly retired within it, the illusion is strong that one has seen nothing except in imagination—that there was merely an apparition induced by the magical quality of this world of shifting sand and foaming water.

Since their food-gathering activities keep them in the edge of the surf, mole crabs are exposed to enemies from both land and water—birds that probe in the wet sand, fish that swim in with the tide, feeding in the rising water, blue crabs darting out of the surf to seize them. So the mole crabs function in the sea’s economy as an important link between the microscopic food of the waters and the large, carnivorous predators.

Even though the individual mole crab may escape the larger creatures that hunt the tide lines, the span of life is short, comprising a summer, a winter, and a summer. The crab begins life as a minute larva hatched from an orange-colored egg that has been carried for months by the mother crab, one of a mass firmly attached beneath her body. As the time for hatching nears, the mother foregoes the feeding movements up and down the beach with the other crabs and remains near the zone of the low tide, so avoiding the danger of stranding her offspring on the sands of the upper beach.

When it escapes from the protective capsule of the egg, the young larva is transparent, large-headed, and large-eyed as are all crustacean young, weirdly adorned with spines. It is a creature of the plankton, knowing nothing of life in the sands. As it grows it molts, shedding the vestments of its larval life. So it reaches a stage in which, although still swimming in larval fashion with waving motions of its bristled legs, it now seeks the bottom in the turbulent surf zone, where the waves stir and loosen the sand. Toward the summer’s end there is another molt, this time bringing transformation to the adult stage, with the feeding behavior of the adult crabs.

During the protracted period of larval life, many of the young mole crabs have made long coastwise journeys in the currents, so that their final coming ashore (if they have survived the voyage) may be far from the parental sands. On the Pacific coast, where strong surface currents flow seaward, Martin Johnson found that great numbers of the crab larvae are carried out over oceanic depths, doomed to certain destruction unless they chance to find their way into a return current. Because of the long larval life, some of the young crabs are carried as far as 200 miles offshore. Perhaps in the prevailing coastwise current of Atlantic shores they travel even farther.

With the coming of winter the mole crabs remain active. In the northern part of their range, where frost bites deep into the sands and ice may form on the beaches, they go out beyond the low-tide zone to pass the cold months where a fathom or more of insulating water lies between them and the wintry air. Spring is the mating season and by July most or all of the males hatched the preceding summer have died. The females carry their egg masses for several months until the young hatch; before winter all of these females have died and only a single generation of the species remains on the beach.

The only other creatures regularly at home between the tide lines of wave-swept Atlantic beaches are the tiny coquina clams. The life of the coquinas is one of extraordinary and almost ceaseless activity. When washed out by the waves, they must dig in again, using the stout, pointed foot as a spade to thrust down for a firm grip, after which the smooth shell is pulled rapidly into the sand. Once firmly entrenched, the clam pushes up its siphons. The intake siphon is about as long as the shell and flares widely at the mouth. Diatoms and other food materials brought in or stirred from the bottom by waves are drawn down into the siphon.

Like the mole crabs, the coquinas shift higher or lower on the beach in mass movements of scores or hundreds of individuals, perhaps to take advantage of the most favorable depth of water. Then the sand flashes with the brightly colored shells as the clams emerge from their holes and let the waves carry them. Sometimes other small burrowers move with the coquinas among the waves—companies of the little screw shell, Terebra, a carnivorous snail that preys on the coquina. Other enemies are sea birds. The ring-billed gulls hunt the clams persistently, treading them out of the sand in shallow water.

On any particular beach, the coquinas are transient inhabitants; they seem to work an area for the food it provides, and then move on. The presence on a beach of thousands of the beautifully variegated shells, shaped like butterflies and crossed by radiating bands of color, may mark only the site of a former colony.

Being only briefly and sporadically possessed by the sea in those recurrent periods of the tides’ farthest advance, the high-tide zone on any shore has in its own nature something of the land as well as of the sea. This intermediate, transitional quality pervades not only the physical world of the upper beach but also its life. Perhaps the ebb and flow of the tides has accustomed some of the intertidal animals, little by little, to living out of water; perhaps this is the reason there are among the inhabitants of this zone some who, at this moment of their history, belong neither to the land nor entirely to the sea.

The ghost crab, pale as the dry sand of the upper beaches it inhabits, seems almost a land animal. Often its deep holes are back where the dunes begin to rise from the beach. Yet it is not an air-breather; it carries with it a bit of the sea in the branchial chamber surrounding its gills, and at intervals must visit the sea to replenish the water. And there is another, almost symbolic return. Each of these crabs began its individual life as a tiny creature of the plankton; after maturity and in the spawning season, each female enters the sea again to liberate her young.

If it were not for these necessities, the lives of the adult crabs would be almost those of true land animals. But at intervals during each day they must go down to the water line to wet their gills, accomplishing their purpose with the least possible contact with the sea. Instead of wading directly into the water, they take up a position a little above the place where, at the moment, most of the waves are breaking on the beach. They stand sideways to the water, gripping the sand with the legs on the landward side. Human bathers know that in any surf an occasional wave will tower higher than the others and run farther up the beach. The crabs wait, as if they also know this, and after such a wave has washed over them, they return to the upper beach.

They are not always wary of contact with the sea. I have a mental picture of one sitting astride a sea-oats stem on a Virginia beach, one stormy October day, busily putting into its mouth food particles that it seemed to be picking off the stem. It munched away, intent on its pleasant occupation, ignoring the great, roaring ocean at its back. Suddenly the foam and froth of a breaking wave rolled over it, hurling the crab from the stem and sending both slithering up the wet beach. And almost any ghost crab, hard pressed by a person trying to catch it, will dash into the surf as though choosing a lesser evil. At such times they do not swim, but walk along on the bottom until their alarm has subsided and they venture out again.

Although on cloudy days and even occasionally in full sunshine the crabs may be abroad in small numbers, they are predominantly hunters of the night beaches. Drawing from the cloak of darkness a courage they lack by day, they swarm boldly over the sand. Sometimes they dig little temporary pits close to the water line, in which they lie watching for what the sea may bring them.

The individual crab in its brief life epitomizes the protracted racial drama, the evolutionary coming-to-land of a sea creature. The larva, like that of the mole crab, is oceanic, becoming a creature of the plankton once it has hatched from the egg that has been incubated and aerated by the mother. As the infant crab drifts in the currents it sheds its cuticle several times to accommodate the increasing size of its body; at each molt it undergoes slight changes of form. Finally the last larval stage, called the megalops, is reached. This is the form in which all the destiny of the race is symbolized, for it—a tiny creature alone in the sea—must obey whatever instinct drives it shoreward, and must make a successful landing on the beach. The long processes of evolution have fitted it to cope with its fate. Its structure is extraordinary when compared with like stages of closely related crabs. Jocelyn Crane, studying these larvae in various species of ghost crabs, found that the cuticle is always thick and heavy, the body rounded. The appendages are grooved and sculptured so that they may be folded down tightly against the body, each fitting precisely against the adjacent ones. In the hazardous act of coming ashore, these structural adaptations protect the young crab against the battering of the surf and the scraping of sand.

Once on the beach, the larva digs a small hole, perhaps as protection from the waves, perhaps as a shelter in which to undergo the molt that will transform it into the shape of the adult. From then on, the life of the young crab is a gradual moving up the beach. When small it digs its burrows in wet sand that will be covered by the rising tide. When perhaps half grown, it digs above the high-tide line; when fully adult it goes well back into the upper beach or even among the dunes, attaining then the farthest point of the landward movement of the race.

On any beach inhabited by ghost crabs, their burrows appear and disappear in a daily and seasonal rhythm related to the habits of the owners. During the night the mouths of the burrows stand open while the crabs are out foraging on the beach. About dawn the crabs return. Whether each goes, as a rule, to the burrow it formerly occupied or merely to any convenient one is uncertain—the habit may vary with locality, the age of the crab, and other changing conditions.

Most of the tunnels are simple shafts running down into the sand at an angle of about forty-five degrees, ending in an enlarged den. Some few have an accessory shaft leading up from the chamber to the surface. This provides an emergency exit to be used if an enemy—perhaps a larger and hostile crab-comes down the main shaft. This second shaft usually runs to the surface almost vertically. It is farther away from the water than the main tunnel, and may or may not break through the surface of the sand.

The early morning hours are spent repairing, enlarging, or improving the burrow selected for the day. A crab hauling up sand from its tunnel always emerges sideways, its load of sand carried like a package under the legs of the functional rear end of the body. Sometimes, immediately on reaching the burrow mouth, it will hurl the sand violently away and flash back into the hole; sometimes it will carry it a little distance away before depositing it. Often the crabs stock their burrows with food and then retire into them; nearly all crabs close the tunnel entrances about midday.

All through the summer the occurrence of holes on the beach follows this diurnal pattern. By autumn most of the crabs have moved up to the dry beach beyond the tide; their holes reach deeper into the sand as though their owners were feeling the chill of October. Then, apparently, the doors of sand are pulled shut, not to be opened again until spring. For the winter beaches show no sign either of the crabs or of their holes—from dime-sized youngsters to full-grown adults, all have disappeared, presumably into the long sleep of hibernation. But, walking the beach on a sunny day in April, one will see here and there an open burrow. And presently a ghost crab in an obviously new and shiny spring coat may appear at its door and very tentatively lean on its elbows in the spring sunshine. If there is a lingering chill in the air, it will soon retire and close its door. But the season has turned, and under all this expanse of upper beach, crabs are awakening from their sleep.

Like the ghost crab, the small amphipod known as the sand hopper or beach flea portrays one of those dramatic moments of evolution, in which a creature abandons an old way of life for a new. Its ancestors were completely marine; its remote descendants, if we read its future aright, will be terrestrial. Now it is midway in the transition from a sea life to a land life.

As in all such transitional existences, there are strange little contradictions and ironies in its way of life. The sand hopper has progressed as far as the upper beach; its predicament is that it is bound to the sea, yet menaced by the very element that gave it life. Apparently it never enters the water voluntarily. It is a poor swimmer and may drown if long submerged. Yet it requires dampness and probably needs the salt in the beach sand, and so it remains in bondage to the water world.

The movements of the sand hoppers follow the rhythm of the tides and the alternation of day and night. On the low tides that fall during the dark hours, they roam far into the intertidal zone in search of food. They gnaw at bits of sea lettuce or eelgrass or kelp, their small bodies swaying with the vigor of their chewing. In the litter of the tide lines they find morsels of dead fish or crab shells containing remnants of flesh; so the beach is cleaned and the phosphates, nitrates, and other mineral substances are recovered from the dead for use by the living.

If low water has fallen late in the night, the amphipods continue their foraging until shortly before daybreak. Before light has tinged the sky, however, all of the hoppers begin to move up the beach toward the high-water line. There each begins to dig the burrow into which it will retreat from daylight and rising water. As it works rapidly, it passes back the grains of sand from one pair of feet to the next until, with the third pair of thoracic legs, it piles the sand behind it. Now and then the small digger straightens out its body with a snap, so that the accumulated sand is thrown out of the hole. It works furiously at one wall of the tunnel, bracing itself with the fourth and fifth pairs of legs, then turns and begins work on the opposite wall. The creature is small and its legs are seemingly fragile, yet the tunnel may be completed within perhaps ten minutes, and a chamber hollowed out at the end of the shaft. At its maximum depth this shaft represents as prodigious a labor as though a man, working with no tools but his hands, had dug for himself a tunnel about 60 feet deep.

The work of excavation done, the sand flea often returns to the mouth of its burrow to test the security of the entrance door, formed by the accumulation of sand from the deeper parts of the shaft. It may thrust out its long antennae from the mouth of the burrow, feeling the sand, tugging at the grains to draw more of them into the hole. Then it curls up within the dark snug chamber.

As the tide rises overhead, the vibrations of breaking waves and shoreward-pressing tides may come down to the little creature in its burrow, bringing a warning that it must stay within to avoid water and the dangers brought by water. It is less easy to understand what arouses the protective instinct to avoid daylight, with all the dangers of foraging shore birds. There can be little difference between day and night in that deep burrow. Yet in some mysterious way the beach flea is held within the safety of the sandy chamber until the two essential conditions again prevail on the beach—darkness and a falling tide. Then it awakens from sleep, creeps up the long shaft, and pushes away the sand door. Once again the dark beach stretches before it, and a retreating line of white froth at the edge of the tide marks the boundary of its hunting grounds.

Each den that is dug with so much labor is merely a shelter for one night, or one tidal interval. After the low-tide feeding period, each hopper will dig itself a new refuge. The holes that we see on the upper beach lead down to empty burrows from which the former occupants have gone. An occupied burrow has its “door” closed, and so its location cannot easily be detected. On the sandy edge of the sea there is, then, the abundant life of protected beaches and shoals, the sparse life of surf-swept sands, and the pioneering life that has reached the high-tide line and seems poised in space and time for invasion of the land.

But the sands contain also the record of other lives. A thin net of flotsam is spread over the beaches—the driftage of ocean brought to rest on the shore. It is a fabric of strange composition, woven with tireless energy by wind and wave and tide. The supply of materials is endless. Caught in the strands of dried beach grass and seaweeds there are crab claws and bits of sponge, scarred and broken mollusk shells, old spars crusted with sea growths, the bones of fishes, the feathers of birds. The weavers use the materials at hand, and the design of the net changes from north to south. It reflects the kind of bottom offshore—whether rolling sand hills or rocky reefs; it subtly hints of the nearness of a warm, tropical current, or tells of the intrusion of cold water from the north. In the litter and debris of the beach there may be few living creatures, but there is the suggestion, the intimation of a million, million lives, lived in the sands nearby or brought to this place from far sea distances.

In the beach flotsam there are often strays from the surface waters of the open ocean, reminders of the fact that most sea creatures are the prisoners of the particular water masses they inhabit. When tongues of their native waters, driven by winds or drawn by varying temperature or salinity patterns, stray into unaccustomed territory, this drifting life is carried involuntarily with them.

In the several centuries that men of inquiring mind have been walking the world’s shores many unknown sea animals have been discovered as strays from the open ocean in the flotsam of the tide lines. One such mysterious link between the open sea and the shore is the ramshorn shell, Spirula. For many years only the shell had been known—a small white spiral forming two or three loose coils. By holding such a shell to the light, one can see that it is divided into separate chambers, but seldom is there a trace of the animal that built and inhabited it. By 1912, about a dozen living specimens had been found, but still no one knew in what part of the sea the creature lived. Then Johannes Schmidt undertook his classic researches into the life history of the eel, crossing and recrossing the Atlantic and towing plankton nets at different levels from the surface down into depths perpetually black. Along with the glass-clear larvae of the eels that were the object of his search, he brought up other animals—among them many specimens of Spirula, which had been caught swimming at various depths down to a mile. In their zone of greatest abundance, which seems to lie between 900 and 1500 feet, they probably occur in dense schools. They are little squidlike animals with ten arms and a cylindrical body, bearing fins like propellers at one end. Placed in an aquarium, they are seen to swim with jerky, backward spurts of jet-propelled motion.

It may seem mysterious that the remains of such a deep-sea animal should come to rest in beach deposits, but the reason is, after all, not obscure. The shell is extremely light; when the animal dies and begins to decay, the gases of decomposition probably lift it toward the surface. There the fragile shell begins a slow drift in the currents, becoming a natural “drift bottle” whose eventual resting place is a clue not so much to the distribution of the species as to the course of the currents that bore it. The animals themselves live over deep oceans, perhaps most abundantly above the steep slopes that descend from the edges of the continents into the abyss. In such depths, they seem to occupy tropical and subtropical belts around the world. Now, in this little shell curved like the horn of a ram, we have one of the few persisting reminders of the days when great, spiral-shelled “cuttle fish” swarmed in the oceans of the Jurassic and earlier periods. All other cephalopods, except the pearly or chambered nautilus of the Pacific and Indian Oceans, have either abandoned their shells or converted them to internal remnants.

And sometimes, among the tidal debris, there appears a thin papery shell, bearing on its white surface a ribbed pattern like that which shore currents impress upon the sand. It is the shell of the paper nautilus or argonaut, an animal distantly related to an octopus, and like it having eight arms. The argonaut lives on the high seas, in both Atlantic and Pacific Oceans. The “shell” is actually an elaborate egg case or cradle secreted by the female for the protection of her young. It is a separate structure that she can enter or leave at will. The much smaller male (about one tenth the size of his mate) secretes no shell. He inseminates the female in the strange manner of some other cephalopods: one of his arms breaks off and enters the mantle cavity of the female, carrying a load of spermatophores. For a long while the male of this creature went unrecognized. Cuvier, a French zoologist of the early nineteenth century, was familiar with the detached arm but supposed it to be an independent animal, probably a parasitic worm. The argonaut is not the chambered or pearly nautilus of Holmes’s famous poem. Although also a cephalopod, the pearly nautilus belongs to a different group and bears a true shell secreted by the mantle. It inhabits tropical seas, and like Spirula is a descendant of the great spiral-shelled mollusks that dominated the seas of Mesozoic times.

Storms bring in many strays from tropical waters. In a shell shop at Nags Head, North Carolina, I once attempted to buy the beautiful violet snail, Janthina. The proprietor of the shop refused to sell this, her only specimen. I understood why when she told me of finding the living Janthina on the beach after a hurricane, its marvelous float still intact, and the surrounding sand stained purple as the little animal tried, in its extremity, to use its only defense against disaster. Later I found an empty shell, light as thistledown, resting in a depression in the coral rock of Key Largo, where some gentle tide had laid it. I have never been so fortunate as my acquaintance at Nags Head, for I have never seen the living animal.

Janthina is a pelagic snail that drifts on the surface of the open ocean, hanging suspended from a raft of frothy bubbles. The raft is formed from mucus that the animal secretes; the mucus entraps bubbles of air, then hardens into a firm, clear substance like stiff cellophane. In the breeding season the snail fastens its egg capsules to the under side of the raft, which throughout the year serves to keep the little animal afloat.

Like most snails, Janthina is carnivorous; its prey is found among other plankton animals, including small jellyfishes, crustaceans, and even small goose barnacles. Now and then a swooping gull drops from the sky and takes a snail—but for the most part the bubble raft must be excellent camouflage, almost indistinguishable from a bit of drifting sea froth. There must be other enemies that come from below, for the blue-to-violet tints of the shell (which hangs below the raft) are the colors worn by many creatures that live at or near the surface film and need to conceal themselves from enemies looking up from below.

The strong northward flow of the Gulf Stream bears on its surface fleets of living sails—those strange coelenterates of the open sea, the siphonophores. Because of adverse winds and currents these small craft sometimes come into shallow water and are stranded on the beaches. This happens most often in the south, but the southern coast of New England also receives strays from the Gulf Stream, for the shallows west of Nantucket act as a trap to collect them. Among such strays, the beautiful azure sail of the Portuguese man-of-war, Physalia, is known to almost everyone, for so conspicuous an object can hardly be missed by any beach walker. The little purple sail, or by-the-wind sailor, Velella, is known to fewer, perhaps because of its much smaller size and the fact that once left on the beach it dries quickly to an object that is hard to identify. Both are typically inhabitants of tropical waters, but in the warmth of the Gulf Stream they may sometimes go all the way across to the coast of Great Britain, where in certain years they appear in numbers.

In life the oval float of Velella is a beautiful blue color, with a little elevated crest or sail passing diagonally across it. The disc is about an inch and a half long and half as wide. This is not one animal but a composite one, or colony of inseparably associated individuals—the multiple offspring of a single fertilized egg. The various individuals carry on separate functions. A feeding individual hangs suspended from the center of the float. Small reproductive individuals cluster around it. Around the periphery of the float, feeding individuals in the form of long tentacles hang down to capture the small fry of the sea.

A whole fleet of Portuguese men-of-war is sometimes seen from vessels crossing the Gulf Stream when some peculiarity of the wind and current pattern has brought together a number of them. Then one can sail for hours or days with always some of the siphonophores in sight. With, the float or sail set diagonally across its base, the creature sails before the wind; looking down into the clear water one can see the tentacles trailing far below the float. The Portuguese man-of-war is like a small fishing boat trailing a drift net, but its “net” is more nearly like a group of high-voltage wires, so deadly is the sting of the tentacles to almost any fish or other small animal unlucky enough to encounter them.

The true nature of the man-of-war is difficult to grasp, and indeed many aspects of its biology are unknown. But, as with Velella, the central fact is that what appears to be one animal is really a colony of many different individuals, although no one of them could exist independently. The float and its base are thought to be one individual; each of the long trailing tentacles another. The food-capturing tentacles, which in a large specimen may extend down for 40 or 50 feet, are thickly studded with nematocysts or stinging cells. Because of the toxin injected by these cells, Physalia is the most dangerous of all the coelenterates.

For the human bather, even glancing contact with one of the tentacles produces a fiery welt; anyone heavily stung is fortunate to survive. The exact nature of the poison is unknown. Some people believe there are three toxins involved, one producing paralysis of the nervous system, another affecting respiration, the third resulting in extreme prostration and death, if a large dose is received: In areas where Physalia is abundant, bathers have learned to respect it. On some parts of the Florida coast the Gulf Stream passes so close inshore that many of these coelenterates are borne in toward the beaches by onshore winds. The Coast Guard at Lauderdale-by-the-Sea and other such places, when posting reports of tides and water temperatures, often includes forecasts of the relative number of Physalias to be expected inshore.

Because of the highly toxic nature of the nematocyst poisons, it is extraordinary to find a creature that apparently is unharmed by them. This is the small fish Nomeus, which lives always in the shadow of a Physalia. It has never been found in any other situation. It darts in and out among the tentacles with seeming impunity, presumably finding among them a refuge from enemies. In return, it probably lures other fish within range of the man-of-war. But what of its own safety? Is it actually immune to the poisons? Or does it live an incredibly hazardous life? A Japanese investigator reported years ago that Nomeus actually nibbles away bits of the stinging tentacles, perhaps in this way subjecting itself to minute doses of the poison throughout its life and so acquiring immunity. But some recent workers contend that the fish has no immunity whatever, and that every live Nomeus is simply a very lucky fish.

The sail, or float, of a Portuguese man-of-war is filled with gas secreted by the so-called gas gland. The gas is largely nitrogen (85 to 91 per cent) with a small amount of oxygen and a trace of argon. Although some siphonophores can deflate the air sac and sink into deep water if the surface is rough, Physalia apparently cannot. However, it does have some control over the position and degree of expansion of the sac. I once had a graphic demonstration of this when I found a medium-size man-of-war stranded on a South Carolina beach. After keeping it overnight in a bucket of salt water, I attempted to return it to the sea. The tide was ebbing; I waded out into the chilly March water, keeping the Physalia in its bucket out of respect for its stinging abilities, then hurled it as far into the sea as I could. Over and over, the incoming waves caught it and returned it to the shallows. Sometimes with my help, sometimes without, it would manage to take off again, visibly adjusting the shape and position of the sail as it scudded along before the wind, which was blowing out of the south, straight up the beach. Sometimes it could successfully ride over an incoming wave; sometimes it would be caught and hustled and bumped along through thinning waters. But whether in difficulty or enjoying momentary success, there was nothing passive in the attitude of the creature. There was, instead, a strong illusion of sentience. This was no helpless bit of flotsam, but a living creature exerting every means at its disposal to control its fate. When I last saw it, a small blue sail far up the beach, it was pointed out to sea, waiting for the moment it could take off again.

Although some of the derelicts of the beach reflect the pattern of the surface waters, others reveal with equal clarity the nature of the sea bottom offshore. For thousands of miles from southern New England to the tip of Florida the continent has a continuous rim of sand, extending in width from the dry sand hills above the beaches far out across the drowned lands of the continental shelf. Yet here and there within this world of sand there are hidden rocky areas. One of these is a scattered and broken chain of reefs and ledges, submerged beneath the green waters off the Carolinas, sometimes close inshore, sometimes far out on the western edge of the Gulf Stream. Fishermen call them “black rocks” because the blackfish congregate around them. The charts refer to “coral” although the closest reef-building corals are hundreds of miles away, in southern Florida.

In the 1940’s, biologist divers from Duke University explored some of these reefs and found that they are not coral, but an outcropping of a soft claylike rock known as marl. It was formed during the Miocene many thousands of years ago, then buried under layers of sediment and drowned by a rising sea. As the divers described them, these submerged reefs are low-lying masses of rock sometimes rising a few feet above the sand, sometimes eroded away to level platforms from which swaying forests of brown sargassum grow. In deep fissures other algae find places of attachment. Much of the rock is smothered under curious sea growths, plant and animal. The stony coralline algae, whose relatives paint the low-tide rocks of New England a deep, old-rose hue, encrust the higher parts of the open reef and fill its interstices. Much of the reef is covered by a thick veneer of twisting, winding, limy tubes—the work of living snails and of tube-building worms, forming a calcareous layer over the old, fossil rock. Through the years the accumulation of algae and the growth of snail and worm tubes have added, little by little, to the structure of the reef.

Where the reef rock is free from crusts of algae and worm tubes, boring mollusks—date mussels, piddocks, and small boring clams—have drilled into it, scraping out holes in which they lodge, while feeding on the minute life of the water. Because of the firm support provided by the reef, gardens of color bloom in the midst of the drabness of shifting sand and silt. Sponges, orange or red or ocher, extend their branches into the currents that drift across the reef. Fragile, delicately branching hydroids rise from the rocks and from their pale “flowers,” in season, tiny jellyfish swim away. Gorgonians are like tall wiry grasses, orange and yellow. And a curious shrubby form of moss animal or bryozoan lives here, the tough and gelatinous structure of its branches containing thousands of tiny polyps, which thrust out tentacled heads to feed. Often this bryozoan grows around a gorgonian, then appearing like gray insulation around a dark, wiry core.

Were it not for the reefs, none of these forms could exist on this sandy coast. But because, through the changing circumstances of geologic history, the old Miocene rocks are now cropping out on this shallow sea floor, there are places where the planktonic larvae of such animals, drifting in the currents, may end their eternal quest for solidity.

After almost any storm, at such places as South Carolina’s Myrtle Beach, the creatures from the reefs begin to appear on the intertidal sands. Their presence is the visible result of a deep turbulence in the offshore waters, with waves reaching down to sweep violently over those old rocks that have not known the crash of surf since the sea drowned them, thousands of years ago. The storm waves dislodge many of the fixed and sessile animals and sweep off some of the free-living forms, carrying them away into an alien world of sandy bottoms, of waters shallowing ever more and more until there is no more water beneath them, only the sands of the beach.

I have walked these beaches in the biting wind that lingers after a northeast storm, with the waves jagged on the horizon and the ocean a cold leaden hue, and have been stirred by the sight of masses of the bright orange tree sponge lying on the beach, by smaller pieces of other sponges, green and red and yellow, by glistening chunks of “sea pork” of translucent orange or red or grayish white, by sea squirts like knobby old potatoes, and by living pearl oysters still gripping the thin branches of gorgonians. Sometimes there have been living starfish—the dark red southern form of the rock-dwelling Asterias. Once there was an octopus in distress on the wet sands where the waves had thrown it. But life was still in it; when I helped it out beyond the breakers it darted away.

Pieces of the ancient reef itself are commonly found on the sand at Myrtle Beach and presumably at any place where such reefs lie offshore. The marl is a dull gray cement-like rock, full of the borings of mollusks and sometimes retaining their shells. The total number of borers is always so great that one thinks how intense must be the competition, down on that undersea rock platform, for every available inch of solid surface, and how many larvae must fail to find a footing.

Another kind of “rock” occurs on the beach in chunks of varied size and perhaps even more abundantly than the marl. It has almost the structure of honeycomb taffy, being completely riddled with little twisting passageways. The first time one sees this on the beach, especially if it is half buried in sand, one might almost take it for one of the sponges, until investigation proves it to be hard as rock. It is not of mineral origin, however—it is built by small sea worms, dark of body and tentacled of head. These worms, living in aggregations of many individuals, secrete about themselves a calcareous matrix, which hardens to the firmness of rock. Presumably it thickly encrusts the reefs or builds up solid masses from a rocky floor. This particular kind of “worm rock” had not been known from the Atlantic coast until Dr. Olga Hartman identified my specimens from Myrtle Beach as “a matrix-building species of Dodecaceria” whose closest relatives are Pacific and Indian Ocean inhabitants. How and when did this particular species reach the Atlantic? How extensive is its range there? These and many other questions remain to be answered; they are one small illustration of the fact that our knowledge is encompassed within restricted boundaries, whose windows look out upon the limitless spaces of the unknown.

On the upper beach, beyond the zone where the flood tide returns the sea water twice daily, the sands dry out. Then they are subjected to excesses of heat; their arid depths are barren, with little to attract life, or even to make life possible. The grains of dry sands rub one against another. The winds seize them and drive them in a thin mist above the beach, and the cutting edge of this wind-driven sand scours the driftwood to a silver sheen, polishes the trunks of old derelict trees, and scourges the birds that nest on the beach.

But if this area has little life within itself, it is full of the reminders of other lives. For here above the high-tide line, all the empty shells of the mollusks come to rest. Visiting the beach that borders Shackleford Shoals in North Carolina or Florida’s Sanibel Island, one could almost believe that mollusks are the only inhabitants of the sea’s edge, for their enduring remains dominate the beach debris long after the more fragile remnants of crabs and sea urchins and starfish have been returned to the elements. First the shells were dropped low on the beach by the waves; then, tide by tide, they were moved up across the sands to the line of the highest of the high tides. Here they will remain, till buried in drifting sand or carried away in a wild carnival of storm surf.

From north to south the composition of the shell windrows changes, reflecting the changing communities of the mollusks. Every little pocket of gravelly sand that accumulates in favorable spots amid the rocks of northern New England is strewn with mussels and periwinkles. And when I think of the sheltered beaches of Cape Cod I see in memory the windrows of jingle shells being shifted gently by the tide, their thin, scale-like valves (how can they house a living creature?) gleaming with a satin sheen. The arched upper valve occurs more often in beach flotsam than the flat lower one, which is perforated by a hole for the passage of the strong byssus cord that attaches the jingle to a rock or to another shell. Silver, gold, and apricot are the colors of the jingles, set against the deep blue of the mussels that dominate these northern shores. And scattered here and there are the ribbed fans of the scallops and the little white sloops of the boat shells stranded on the beach. The boat shell is a snail with a curiously modified shell, having a little “half deck” on the lower surface. It often becomes attached to its fellows in chains of half a dozen or more individuals. Each boat shell is in its lifetime first male then female. In the chains of attached shells those at the bottom of the chain are always females, the upper animals males.

On the Jersey beaches and the coastal islands of Maryland and Virginia the massive structure of the shells and the lack of ornamental spines have a meaning—that the offshore world of shifting sand is deeply stirred by the endless processions of the waves that roll in on this coast. The thick shell of the surf clam is its defense against the force of the waves. These shores are strewn, too, with the heavy armaments of the whelks, and with the smooth globes of the moon snails.

From the Carolinas south the beach world seems to belong to the several species of arks, whose shells outnumber all others. Though variously shaped, their shells are stout, with long straight hinges. The ponderous ark wears a black, beardlike growth, or periostracum, heavy in fresh specimens, scanty or absent in beach-worn shells. The turkey wing is a gaily colored ark, with reddish bands streaking its yellowish shell. It, too, wears a thick periostracum, and lives down in deep offshore crevices, where it attaches itself to rocks or any other support by a strong line or byssus. While a few kinds of arks extend the range of these mollusks throughout New England (for example, the small transverse ark and the so-called bloody clam—one of the few mollusks that has red blood) it is on southern beaches that the group becomes dominant. On famed Sanibel Island on the west coast of Florida, where the variety of shells is probably greater than anywhere else on our Atlantic coast, the arks nevertheless make up about 95 per cent of the beach deposits.

The pen shells begin to appear in numbers on the beaches below Capes Hatteras and Lookout, but perhaps they, too, live in the most prodigious numbers on the Gulf coast of Florida. I have seen truckloads of them on the beach at Sanibel even in calm winter weather. In a violent tropical hurricane the destruction of this light-shelled mollusk is almost incredible. Sanibel Island presents about fifteen miles of beach to the Gulf of Mexico. On this strand, it has been estimated, about a million pen shells have been hurled by a single storm, having been torn loose by waves reaching down to bottoms lying as deep as 30 feet. The fragile shells of the pens are ground together in the buffeting of storm surf; many are broken, but even those not so destroyed have no way of returning to the sea, and so are doomed. As if knowing this, the commensal pea crabs that inhabit them creep out of the shells like the proverbial rats abandoning a sinking ship; they may be seen by the thousand swimming about in apparent bewilderment in the surf.

The pen shells spin anchoring byssus threads of golden sheen and remarkable texture; the ancients spun their cloth of gold from the byssus of the Mediterranean pens, producing a fabric so line and soft it could be drawn through a finger ring. The industry persists at Italian Taranto, on the Ionian Sea, where gloves and other small garments are woven of this natural fabric as curios or tourists’ souvenirs.

The survival of an undamaged angel wing in the debris of the upper beach seems extraordinary, so delicately fragile does it appear. Yet these valves of purest white, when worn by the living animals, are capable of penetrating peat or firm clay. The angel wing is one of the most powerful of the boring clams and, having very long siphons with which to maintain communication with the sea water, is able to burrow deeply. I have dug for them in peat beds in Buzzards Bay, and have found them on beach exposures of peat on the coast of New Jersey, but their occurrence north of Virginia is local and rare.

This purity of color, this delicacy of structure are buried throughout life in a bank of clay, for the angel wing’s beauty seems destined to be hidden from view until, after the death of the animal, the shells are released by the waves and carried to the beach. In its dark prison the angel wing conceals an even more mysterious beauty. Secure from enemies, hidden from all other creatures, the animal itself glows with a strange green light. Why? For whose eyes? For what reason?

Besides the shells, there are other objects in the beach flotsam that are mysterious in shape and texture. Flat, horny or shell-like discs of various shapes and sizes are the opercula of sea snails—the protective doors that close over the opening when the animal has withdrawn into its shell. Some opercula are round, some leaf-shaped, some like slender, curving daggers. (The “cat’s eye” of the South Pacific is the operculum of a snail, rounded on one surface and polished like a boy’s marble.) The opercula of the various species are so characteristic in shape, material, and structure that they are a useful means of identifying otherwise difficult species.

The tidal flotsam abounds, too, in many little empty egg cases in which various sea creatures passed their first days of life. These are of various shapes and materials. The black “mermaid’s purses” belong to one of the skates. They are flat, horny rectangles, with two long, curling prongs or tendrils extending from each end. With these the parent skate attaches the packet containing a fertilized egg to seaweeds on some offshore bottom. After the young skate matures and hatches, its discarded cradle is often washed up on the beach. Egg cases of the banded tulip shell remind one of the dried seed pods of a flower, a cluster of thin, parchment-like containers borne on a central stalk. Those of the channeled or the knobbed whelks are long, spiraling strings of little capsules, again parchment-like in texture. Each of the flat, ovoid capsules contains scores of baby whelks, incredible in the minute perfection of their shells. Sometimes a few remain in an egg string found on the beach; they rattle against the hard walls of the capsule like peas in a dried pod.

Perhaps the most baffling of all objects found on beaches are the egg cases of the sand collar snail or moon snail. If someone had cut a doll’s shoulder cape out of a piece of fine sandpaper, the result would be about the same. The “collars” produced by the various species of the family of moon snails differ in size and, though slightly, in shape. In some the edges are smooth, in others scalloped. The arrangement of the eggs also follows slightly different patterns in the various species. This strange receptacle for the eggs of the snail is formed as a sheet of mucus pushed out from under the foot and molded on the outside of the shell. This results in the collar shape. The eggs are attached to the under side of the collar, which becomes completely impregnated with sand grains.

Mingled with the bits and fragments of sea creatures are the reminders of man’s invasion of the sea—spars, pieces of rope, bottles, barrels, boxes of many shapes and sizes. If these have been long at sea, they bring their own collection of sea life, for in their period of drifting in the currents, they have served as a solid place of attachment for the searching larvae of the plankton.

On our Atlantic coast, the days following a northeast blow or a tropical storm are a time to look for the driftage of open ocean. I remember such a day on the beach at Nags Head, after a hurricane had passed by at sea during the night. The wind was still blowing a gale; there was a fine wild surf. That day the beach was strewn with many bits of driftwood, branches of trees, and heavy planks and spars, many of which bore growths of Lepas, the gooseneck barnacle of the open sea. One long plank was studded with tiny barnacles the size of a mouse’s ear; on some of the other drifted timbers the barnacles had grown to a length of an inch or more, exclusive of the stalk. The size of the encrusting barnacles is a rough index of the time the spar has been at sea. In the profusion of their growth on almost every piece of timber one senses the incredible abundance of barnacle larvae drifting in the sea, ready to grasp any firm object adrift in their fluid world, for by strange irony none of them could complete their development in the sea water alone. Each of those weird-looking little beings, rowing through the water with feathered appendages, had to find a hard surface to which it could attach before assuming the adult form.

The life history of these stalked barnacles is very similar to that of the acorn barnacles of the rocks. Within the hard shells is a small crustacean body, bearing feathered appendages with which to sweep food into their mouths. The chief difference is that the shells are borne on a fleshy stalk instead of arising from a flat base firmly cemented to the substratum. When the animals are not feeding, the shells can be tightly closed, as in the rock barnacle; when they open to feed, there are the same sweeping, rhythmical motions of the appendages.

Seeing on the shore a branch from some tree that evidently has been long adrift and now is generously sprinkled with the fleshy brown stalks and the ivory-hued shells of the barnacle, with their marginal tints of blue and red, one can remember with tolerant understanding the old medieval misconception that conferred on these strange crustaceans the name “goose barnacle.” The seventeenth-century English botanist John Gerard compiled a description of the “goose tree” or “Barnakle tree” on the basis of the following experience: “Traveling upon the shores of our English coast between Dover and Rummey, I founde the trunke of an olde rotten tree, which … we drewe out of the water upon dry lande; on this rotten tree I founde growing many thousands of long crimson bladders … at the neather end whereof did grow a shell fish, fashioned somewhat like a small Muskle … which after I had opened … I found living things that were very naked, in shape like a Birde; in others, the Birde covered with soft downe, the shell halfe open, and the Birde readie to fall out, which no doubt were the foules called Barnakles.” Evidently Gerard’s imaginative eye saw in the appendages of the barnacles the resemblance to a bird’s feathers. On this slender basis he built the following pure fabrication: “They spawne as it were in March and April; the Geese are formed in Maie and June, and come to fulnesse of feathers in the moneth after.” And so in many an old work of un-natural history from this time on, we see drawings of trees bearing fruit in the form of barnacles, and geese emerging from the shells to fly away.

Old spars and water-soaked timbers cast on the beach are full of the workings of the shipworm—long cylindrical tunnels penetrating all parts of the wood. Usually nothing remains of the creatures themselves except occasional fragments of their small calcareous shells; these proclaim that the shipworm is a true mollusk, despite its long, slender, and wormlike body.

There were shipworms long before there were men; yet within his own short tenancy of earth, man has greatly increased their numbers. The shipworm can live only in wood; if its young fail to discover some woody substance at a critical period of their existence, they die. This absolute dependence of a sea creature on something derived from the continents seems strange and incongruous. There could have been no shipworms until woody plants evolved on land. Their ancestors probably were clamlike forms burrowing in mud or clay, merely using their excavated holes as a base from which to extract the plankton of the sea. Then after trees evolved, these forerunners of the shipworms adapted themselves to a new habitat—the relatively few forest trees brought into the sea by rivers. But their numbers over all the earth must have been small until, scant thousands of years ago, men began to send wooden vessels across the sea and to build wharves at its edge; in all such wooden structures, the shipworm found a greatly extended range, to the cost of the human race.

The shipworm’s place in history is secure. It was the scourge of the Romans with their galleys, of the seagoing Greeks arid Phoenicians, of the explorers of the New World. In the 1700’s it riddled the dikes that the Dutch had built to keep out the sea; by so doing it threatened the very life of Holland. (As an academic by-product, the first extensive studies of the shipworm were made by Dutch scientists, to whom knowledge of its biology had become a matter of life and death. Snellius, in 1733, pointed out for the first time that this animal is a clamlike mollusk, not a worm.) About 1917 the shipworm invaded the harbor of San Francisco. Before its inroads were even suspected, ferry slips had begun to collapse, and wharves and loaded freight cars fell into the harbor. During the Second World War, especially in all tropical waters, the shipworm was an unseen but powerful enemy.

The female of the common shipworm retains the young in her burrow until they have attained the larval stage. Then they are launched into the sea—each a tiny being enclosed in two protective shells, looking like any other young bivalve. If it encounters wood when it has reached the threshold of adulthood, all goes well. It puts out a slender byssus thread as an anchor, a foot develops, and the shells become modified into efficient cutting tools, for rows of sharp ridges appear on their outer surfaces. The burrowing begins. With a powerful muscle, the animal scrapes the ridged shell against the wood, revolving meanwhile so that a smooth, cylindrical burrow is cut. As the burrow is extended, usually with the grain of the wood, the body of the shipworm grows. One end remains attached to the wall near the tiny point of entrance. This bears the siphons through which contact with the sea is maintained. The penetrating end carries the small shells. Between stretches a body that is thin as a lead pencil, but may reach a length of eighteen inches. Although a timber may be infested with hundreds of larvae, the burrows of the shipworms never interfere with each other. If an animal finds itself coming close to another burrow, it invariably turns aside. As it bores, it passes the loosened fragments of wood through its digestive tract. Some of the wood is digested and converted into glucose. This ability to digest cellulose is rare in the animal world—only certain snails, certain insects, and a very few others possess it. But the shipworm makes little use of this difficult art, and feeds chiefly on the rich plankton streaming through its body.

Other timbers on the beach bear the marks of the wood piddock. These are shallow holes that penetrate only the outer portions just beneath the bark, but they are broad and cleanly cylindrical. The boring piddock is seeking only shelter and protection. Unlike the shipworm, it does not digest the wood, but lives only on the plankton that it draws into its body through a protruding siphon.

Empty piddock holes sometimes attract other lodgers, as abandoned birds’ nests may become homes for insects. On the muddy banks of salt creeks at Bears Bluff in South Carolina, I have picked up timbers riddled with holes. Once stout little white-shelled piddocks dwelt in them. The piddocks were long since dead and even the shells were gone, but in each hole was a dark glistening body like a raisin embedded in a cake. They were the contracted tissues of small anemones, finding there, in this world of silt-laden water and yielding mud, that bit of firm foundation which anemones must have. Seeing anemones in such an improbable place, one wonders how the larvae happened to be there, ready to seize the chance opportunity presented by that timber with its neatly excavated apartments; and one is struck anew by the enormous waste of life, remembering that for each of these anemones that succeeded in finding a home, many thousands must have failed.

Always, then, in this flotsam and jetsam of the tide lines, we are reminded that a strange and different world lies offshore. Though what we see here may be but the husks and fragments of life, through it we are made aware of life and death, of movement and change, of the transport of living things by ocean currents, by tides, by wind-driven waves. Some of these involuntary migrants are adults. They may perish in mid-journey; a few, being transported into a new home and finding there conditions that are favorable, may survive, may even produce surviving young to extend the range of the species. But many others are larvae, and whether or not they will make a successful landing depends on many things—on the length of their larval life (can they wait for a distant landfall before they reach the stage when they must take up an adult existence?)—on the temperature of the water they encounter—on the set of the currents that may carry them to favoring shoals, or off into deep water where they will be lost.

And so, walking the beach, we become aware of a most fascinating problem—the colonization of the shore, and especially of those “islands” of rock (or the semblance of rock) that occur in the midst of a sea of sand. For whenever a seawall is built, or a jetty, or pilings are sunk for a pier or a bridge, or rock, long hidden from sun and buried even beneath the sea, emerges again on the ocean floor, these hard surfaces immediately become peopled with typical animals of the rocks. But how did the colonizing rock fauna happen to be at hand—here in the midst of a sandy coast that stretches for hundreds of miles to north and south?

Pondering the answer, we become aware of that ceaseless migration, for the most part doomed to futility, yet ensuring that always, when opportunity arises, Life shall be waiting, ready to take advantage. For the ocean currents are not merely a movement of water; they are a stream of life, carrying always the eggs and young of countless sea creatures. They have carried the hardier ones across oceans, or step by step on long coastwise journeys. They have carried some along deep, hidden passageways where cold currents flow along the floor of the ocean. They have brought inhabitants to populate new islands pushing above the surface of the sea. These things they have done, we must suppose, since first there was life in the sea.

And as long as the currents move on their courses there is the possibility, the probability, even the certainty, that some particular form of life will extend its range, will come to occupy new territory.

As almost nothing else does, this to me expresses the pressure of the life force—the intense, blind, unconscious will to survive, to push on, to expand. It is one of life’s mysteries that most of the participants in this cosmic migration are doomed to failure; it is no less mysterious that their failure turns into success when, for all the billions lost, a few succeed.