The exhaustive, authoritative, weighty and apparently fertile "Oxford Companion to Wine" has given birth to a daughter, "The Oxford Companion to the Wines of North America" (Oxford University Press, $45). The new child came into the world earlier this month and weighs in at a healthy 3 pounds, 6 ounces. And if you already own the 6.5 pound mother book, edited by Jancis Robinson, it's time to add another shelf support and bring home the baby, edited by Bruce Cass and for which Robinson served as consultant editor. The resemblance is uncanny. Like her mother before her, this new "Companion" cracks the wine code through an extensively researched and footnoted encyclopedic A-to-Z guide to North American wine minutiae, from "Active Dry Yeast," a preparation of selected strains of wine yeast used to start fermentation, to "Ziraldo, Donald," the first Canadian after Prohibition to apply for a license to make and sell wine. In between, entries on specific wineries and regions and topics such as package-store sales and three-tier distribution shed new light on the products and the trade. Like low-tech hyperlinks, small-cap text cross-references other topics within the book. But the daughter "Companion" also regularly defers to the well-aged wisdom of her parent through extensive and helpful cross-referencing between books. While helpful, this respectful deference makes these Companions inseparable. An improvement over the mother book is the series of 15 essays that form an extended introduction to the general subject of wine in North America. A nifty seven-pager provides a judiciously detailed parabolic history of the introduction, production and consumption of wine on this continent. Others discuss vineyard labor, media coverage, distribution and general quality. A thoroughly well-done section on the mid-Atlantic contributed by Richard G. Leahy, editor at Vineyard & Winery Management magazine and former resident of Charlottesville who has been tracking Virginia wine since its rebirth in 1979, offers a clinically objective account of winemaking in the region. His Virginia section has objectively good things to say about the local wine. "I think it's a real mark of the evolution of the industry that it gets a fair place in this book," Leahy says. "Virginia, along with the East, has been overlooked for a long time." For those who remain skeptical of the quality of Virginia wine, Leahy cites the recent Eastern International Wine Competition, an industry event, where two Virginia wines, both red, won double gold medals along with 30 other wines out of 1,400 entries from around the world, including a number from California. One of the two double golds, Valhalla Vineyards' Gotterdamerung, a Bordeaux-style blend (the other was Jefferson Vineyards 1998 Cabernet Sauvignon), also won judges' favorite. "The industry is going to continue to evolve and get a reputation as one of America's leading regions," Leahy says.