``America is a culture whose identity is best found in time,'' asserts Gollub, a gerontologist, and that is precisely where he searches for it here, examining seven ``generations'' from the ``Children of the Century,'' born between 1900 and 1909, to the ``Techno-Kids'' born in the 1960's. Gollub's reason for using decades to divide age groups is not clear but appears to be based partly on convenience. It's certainly tidy, but societies don't necessarily shift gears with such regularity. His approach, dubbed the Life Span Framework, considers so-called Time Signatures, the key historical events that have affected each decade's cohorts; their Birthmarks, or representative personality types; Rites of Passage, significant stages in their personal development; and their Weather Report, that is, the economic, cultural, social, political, and technological conditions that shape their values. Gollub tracks the life story of each generation in a sort of vest-pocket cultural history of 20th-century America, and he includes profiles of representative personality types for each group. Finally, he takes a stab at forecasting what the future holds for each group and its specific personality types. His writing smacks of the lingo of market research reports. Catchy names abound; e.g., the four personality types of the Techno-Kids are labeled the 'Billy Budds,' the 'Cosmopolitans,' the 'Missing Ingredients,' and the 'Keepers of the Flame.' Entertaining but repetitious: market research demographics and pop history, dressed up with some basic sociology and psychology.