"A beach stores sand in the dunes behind it," said Bob Taylor, a coastal geologist with the Geological Survey of Canada. "When it's attacked, it draws material from the dunes for itself and for building a protective shoal or bar offshore. When it's less stressed, it takes sand and gravel from offshore and stores it back on the beach and in the dunes."

"You talk as though the damn thing were alive," said Silver Donald Cameron.

"I think of it that way," said Taylor. And so began an odyssey -- an odyssey which would take Cameron into labs, studios, surf shops and libraries, and down both coasts of North America. Beaches, he would find, are indeed like living creatures: they grow, they die, they feed, they starve, they respond to stress, they adapt to change. They are among the most mysterious, alluring and implacable features in our environment.

How do beaches function? Where do the waves come from, and why are they always parallel to the shore, no matter which way the shore faces? Where does sand come from, and why are some beaches grey, some white, some beige? What plants and animals live there, and how do they deal with this harsh, plastic environment?

What do beaches mean to humans? Arrivals and departures, invasions and migrations, the first contact between the explorers and the indigenous peoples -- they all take place in that sandy zone where the sea meets the land. When a film actor walks alone on a beach, the viewer knows s/he is contemplating change or reacting to it. On the summer sands, bishops and judges and executives become children again, building structures which they know the sea will destroy.

But what do humans mean to beaches? As people all over the wealthy industrialized world move to the coasts, they erect barricades of apartment towers and high-rise hotels on shifting sands and crumbling cliffs. The owners defend their position with seawalls, groins and breakwaters, seeking to fortify themselves against the inevitable. But the ocean has an awesome capacity for occasional violence. As sea level and coastal population rise in tandem, the prospect of major disasters rises dramatically.

The beach is also a place where "the mechanical philosophy" of Newton -- which dominated Western thought for three centuries -- meets the new story in science, a story increasingly focussed on unity, order and the relatedness of all things. Why is there order in the universe, and how is order related to "life" and to evolution? Is evolution finished, or has it moved on to higher levels of organization? What does it actually mean to say that something is "living?"

Ultimately, the beach is not a place but a process, perhaps even literally a living process. Like other natural phenomena, the beach is indifferent to our wishes. The beaches were here long before we arrived, and they will be here long after we are gone. In the end, all we can do is cherish and respect them during our own brief dance upon the moving sands.