Two years ago Doig dazzled us with This House of Sky, a luminous memoir of his Montana boyhood. ""I had some knack then for living at the edges of other people's existences,"" he wrote, etching the scabbed countryside and its thrifty inhabitants in rich prose. This new book finds the discretionary Westerner again sharing the life of another: James Gilchrist Swan (1816-1900), a Boston-born drifter with frontier talents and a gifted diarist of the late-19th-century Northwest. And while part of Doig's mission here is simply to introduce us to Swan-the-diarist, he is also determined to share his own feelings as the ""Winter Brother"" who discovers Swan and is somehow held by him, sharing Swan's westward urgings. So Doig sifts through the 40-plus volumes of Swan's writings--a record, from the 1850s on, of the transformation of the Puget Sound region--and sees Swan's life in irregular counterpoint to his own. This approach does have its problems: Swan was no Pepys, and his reporter style (""he has,"" says Doig, ""arithmetic in his eye"") combines with Doig's less glittering prose to give this book an odd coloration very different from that of This House of Sky. Moreover, the two men's lives hardly interact neatly--since ""opening the pages of Swan's years is like entering a room filled with jugglers and tumblers and swallowers of flame."" In fact, Swan's experiences include stints as oyster entrepreneur, Indian schoolmaster, customs inspector, Smithsonian correspondent, and ethnological registrar. (The Indians of Cape Flattery, 1870, remains the standard reference on the Makahs; his survey of the Queen Charlotte Islands was also highly esteemed.) And there's a darker side to Swan, too--bouts of drunkenness (excluded from the diaries), occasional gloom--and some familiar pioneer spirits, ""railroad fever"" among them. Above all, how-ever, he was a precise, untiring recorder, often at the heart of the action; and Doig, the habituated sojourner here as before, readily retraces his steps--in a strange and special historical/literary/personal mosaic.