Rock ‘n’ roll is not like a mountainside in which layers of history accumulate and fossilize, waiting for sunburned grad students to dig them up and make notes on each old bone chip. It’s more like a big vat of stew simmering on the stove, constantly being turned and churned, the stuff that’s settled to the bottom regularly brought up to swirl around with the new flavors. So a reunion doesn’t have to be just a cynical attempt to cash in, or some living anachronism poking its head out of a remote Scottish loch. The British quartet Wire, still most venerated for the astonishingly great late-70s albums Pink Flag, Chairs Missing, and 154, proved this with their first reunion, in 1986–though even then plenty of people thought they should have left well enough alone. The creepy low-slung dance pop of the hit-or-miss The Ideal Copy and the nearly flawless four-song EP Snakedrill might have seemed at the time like a crude attempt to “update” their sound, but in retrospect they hold up better than most of what they were assumed to be imitating, and they laid the foundation for the band’s progression over the next few years, which culminated with The Drill in 1991. That record, a strange swan song, consisted of nine new versions of “Drill,” from Snakedrill–one that leaned toward the dance floor, one made of mechanical loops, one that surged toward the tribal heights of Can, and so on–and what then seemed like a manifestation of obsessive-compulsive disorder now sounds like a premonition of the current fascination with the possibilities of repetition and endless subtle variation. After they reunited the first time, the band refused to play its early material live, and in 1987 showed either disdain or good humor, depending on your perspective, by letting a cover band (the Ex-Lion Tamers, featuring Jim DeRogatis) perform Pink Flag in its entirety as an opening act. Drummer Robert Gotobed is now a farmer, but guitarists Colin Newman and Bruce Gilbert and to a lesser extent bassist Graham Lewis have tried to keep moving since the second breakup, experimenting in various strains of electronic music (Gilbert’s last appearance here, in 1996, was on a bill with Fushitsusha and Tony Conrad). For this tour, though, they’ve relented, and tunes from Pink Flag, Chairs Missing, and 154 make up a good part of the set list. Maybe they are just cashing in, but word from the road is that they’re playing the oldies with what appears to be genuine joy of rediscovery–and who knows where that might lead. Newman will DJ downstairs in Smart Bar after the show. Wednesday, 10 PM, Metro, 3730 N. Clark; 773-549-0203. MONICA KENDRICK