Kennedy, director of the National Park Service, does better in exposing the prejudices of whites who came across the monuments of prehistoric America than in elucidating the mysteries embodied in these New World Stonehenges. An estimated 30 million Native Americans died of European or African diseases during the century following the conquistadors' appearance in the Western Hemisphere. They left behind significant traces of sophisticated cities, roads, and burial grounds in Memphis, Pittsburgh, Cincinnati, and elsewhere in the Ohio and Mississippi river valleys. Later explorers and soldiers beheld these relics -- which included bits of antiquities, earthen mounds, and various geometrical shapes carved into the landscape -- with wonder, confusion, and obtuseness. Kennedy (Rediscovering America, 1990, etc.) perceptively analyzes how attempts to preserve and interpret Native American arts and architecture often foundered on the ingrained prejudices of even supposedly enlightened whites. (Thomas Jefferson, for example, was slow to shed his belief that Indians were incapable of architectural achievement.) Jeffersonians and Jacksonians found it easier to deprive Native Americans of land if they could deny that the Indians had a culture worth saving. They failed to follow the lead of such respectful figures as Jefferson's Treasury secretary, Albert Gallatin, described by Kennedy as ""the first American statesman to employ the evidence of ancient American architecture to justify exertions to redeem the Republic from racial prejudice."" The American mania for development, combined with dismissive scholarship that credited Indian achievements to fair-skinned ""Welshmen"" who supposedly discovered North America in the Middle Ages, led to a cavalier attitude toward Native American artifacts. By 1948, 90% of the earthen Indian architecture noted in a Smithsonian report 100 years earlier had been lost. Best read as an exploration of colliding cultures rather than an examination of the riddles left behind by Native American builders.