If Ken Burns’s epic Jazz series left you feeling you had just skimmed the surface, the next place to turn is the epic Penguin Guide to Jazz on CD , a near-definitive paperback just out in its fifth edition, 1,725 pages long (Penguin, $24.00). Its two British authors are strongly opinionated, yet the solidity of their opinions, the musical and historical understanding behind them, and the eloquence with which they’re expressed have commended them to a broad following of jazz players and fans. Louis Armstrong and Earl Mines recording together in the late twenties are “great men speaking almost quietly among themselves” in “something like a reluctant farewell to jazz’s first golden age.” Miles Davis’s Plugged Nickel sessions are “the Rosetta Stone of modern jazz: a monumental document written in five subtly and sometimes starkly different dialects but within which much of the music of the post-bop period has been defined and demarcated.”