Since the days when Columbus was thought to have been the first European to reach America, school children have learned that Leif Ericson sailed past earlier. Some now know that it was not Leif but an earlier Viking who sailed past, that Leif spent some time in Vinland, that his brother and then his sister came to settle but got themselves into scrapes with the natives, and that his wicked sister-in-law Gudrid established a colony called Hope and had a son here. All of this is now accepted, essentially as told in the two sagas, one from Greenland and one from Iceland, which Irwin cites and quotes extensively. Less well established, but of increasing scholarly repute, is the archaeological evidence--summarized for a juvenile audience in Golding's Mystery of the Vikings in America (1973)--that Vikings continued to explore America up to the time of Columbus and Cabot; and that they passed through Minnesota in the 14th century, having sailed down the Red River from Hudson's Bay. Seventeenth-century Dutch sailors' reports of blond Eskimos on Baffin Island accord with mention of a group that ""went over to the people of America"" in a later copy of a 1342 entry in the Icelandic Annals. Also in the Annals is the 1121 reference--""perhaps the most tantalizing words in early American history""--to a Bishop going ""in search of Wineland"": most likely, says Irwin, to administer to a Christian flock in Newport, Rhode Island, whose mysterious stone tower was probably built for his protection during the visit. Irwin's closely reasoned but over-orchestrated presentation, with its italicized questions and other bits of rhetorical artifice, could intrigue those readers who do indeed find such matters tantalizing. The same audience will pick up on Irwin's second, just as significant lesson: the one on how history changes with the viewpoint of historians. But keep Golding's Mystery. . . on hand, as the more accessible summary for everyday purposes.