BEFORE I READ Nigel Calder's new book, the words "English Channel" called three things to mind: Durkirk, the invasion of Normandy, and Gertrude Ederle, the first woman to swim the channel. The first two are amply chronicled in this fascinatingly eclectic work. But Gertrude Ederle is nowhere to be found. Her absence was my only real disappointment with The English Channel, and it's probably churlish of me to complain, since in her stead I discovered Matthew Webb, who swam the Channel first, in 1875.

Calder's book is a far-ranging contemplation of a body of water only 350 sea miles long and 20 miles across at its narrowest. An undue share of world-shaping events took place in this tiny piece of geography. And to measure its significance Calder touches on everything from volcanic upheavals to nuclear power controversies, drawing on history, geology, archaeology, etymology, literature, politics, and cultural prejudices.

Thus, the swimmer Webb is part of an account of technological assaults on the Channel: crossings by aircraft (Louis Bleriot in 1909); by balloon (Jean-Pierre-Francois Blanchard in 1785); by sailboard (John van der Starre in 1983); and, for a 1984 Guinness Book of Records stunt, a coordinated effort that included a ferry full of people jogging, roller-skating, hula-hooping, dancing, and cooking their way across the water. It's typical that such information shares a chapter with a discourse on Voltaire and the mutual dislike of the English and the French.

The apparent disorganization is anything but haphazard. Calder's motivating device is a leisurely sail by ketch from the western tip of Brittany along the French coastline to the Belgian border, then across to Dover and west again to the Isles of Scilly. To follow the detailed route, the author has helpfully provided simple maps in each chapter that illustrate everything from lighthouses to geological characteristics, as well as the ins and outs of the coast.

Each cove, beach and harbor offers an excuse to ruminate on events recent and not so recent, on opportunities taken and missed. In Calder's words, "The Channel is an untidy museum, with exhibits set out at random. They will speak for themselves in geographical rather than chronological orders . . . . Each stretch of salt water and coast will evoke a theme that may be prehistoric or ultramodern or something in between . . . ."

Our skipper has great tales to tell, of drifting continents and tectonic collisions and of Bronze Age seafarers. He muses on navigation: how prehistoric mariners found their way with careful observation and sounding leads; what Sir Edmund Halley (yes, that one) discovered about magnetic variation and currents; and why buoys were standarized after a disastrous series of ship collisions in 1971.

The emphasis on maritime matters is serious business, even insinuating itself into chapter titles: Calder heads them "Towards . . . Guernsey . . . Dover . . . Plymouth," since "at sea you should not say you are going 'to' somewhere, because who knows what wind and weather will do? 'Towards' avoids hubris."

IT'S COMMONPLACE to claim that winds, seas and tides have determined the fates of nations, but Calder lays the proof on nearly every page. So we get the drama of the Spanish Armada, first becalmed, then scattered by gales, finally falling prey to Sir Francis Drake and thus forever dashing Spanish hopes for supremacy. And the picture of a frustrated Napoleon, whose plan to invade Britain foundered because it relied on a freak wind that never rose.

Where Naploleon failed, others succeeded. Calder's second big premise is that, contrary to popular opinion, the Channel has never been much of a natural barrier. And he musters hordes of armies in defense of his argument. The pivotal figure, of course, is William the Conqueror. But he's merely the centerpiece in a roster of invaders that stretches back through the Vikings and the Angles, Saxons and Jutes, back to the Romans and the Celts. After the Norman conquest, soldiers continued to cross the Channel in both directions, waging battles that united and broke apart empires. The Channel "was the laboratory where modern nationalism was invented," Calder unabashedly asserts.

That's a pretty strong claim for a mere "puddle" of water. But The English Channel bursts with that kind of energy, reflecting the fits, starts and overlaps of human endeavor against unpredictable nature. It does so with boldness, wit and lively characterizations. (Thank goodness Calder found the territory before James Michener did!)

The book is also crammed with wonderful trivia: the origin of the word "vaudeville," the earliest known description of a tennis match, the rise of seaside resorts, and the physiology of seasickness.

That last nugget neatly introduces the centuries-old notion of a Channel tunnel. Last January Margaret Thatcher and Francois Mitterand finally agreed on a plan that would make the tunnel -- with its lucrative economic plums -- a reality by 1992. Calder believes the project will finally bow to inevitability and take hold at last. But, frankly, I'd forego a high-tech futuristic vision of this vital body of water in favor of the author's intimate and engaging portrait. Ten years from now, we might indeed speed through a subsea link from England to France. But what a wonderful journey we'd miss.