Latin, music has been the greatest outside influence on the popular styles"" of American pop music. True enough (assuming that all the earlier influences--black, European, etc.--are ""inside""); and Roberts goes on, in a drily meticulous, decade-by-decade catalogue, to document the varied blendings-in of a slew of distinct musical forms from Brazil, Argentina, Mexico, and Cuba (""much the greatest, most varied, and most long lasting"" effects). The well-known dance crazes are all here, of course (tango, rumba, conga, mambo), but Roberts also explores much subtler Latin influences on ragtime, Tin Pan Alley, jazz (Cubop, Stan Kenton, Dizzy Gillespie), Broadway, Hollywood, and rock (Santana)--a growing tinge that made Latin rhythms ""an almost subliminal part"" of U.S. pop by the late '40s. And, while doing so, he demonstrates a non-purist, open ear that is rare and welcome in such a specialized study: throughout, he acknowledges the Latin/Afro blend, often inextricable in such cases as New Orleans jazz; and, above all, he is ready to look favorably on the formation of hybrids, even when they mean a dilution of Latin authenticity--he can thus spot the genuine charms in such patently commercialized cross-breeds as Xavier Cugat and Herb Alpert's Tijuana Brass. True, there's a paucity of texture here (the only humor comes from an occasional grand title, like ""I Came, I Saw, I Conga'd""), and Roberts' research is less rigorous when dealing with the less overtly Latin music worlds (Jerry Ross, co-author of ""Hernando's Hideaway,"" is identified as ""Jerry Bach""). But, though too dense with titles and data to afford much narrative pleasure, this is a solid, comprehensive, up-to-date (disco, salsa), and balanced examination--a worthy, sharply-focused addition to the shelves of serious pop-music scholarship.