galvanizing grace of spontaneity, rock becomes a mere diversion: If you're after transcendence, a formulized record is no path to bliss.

While this understanding of rock is too pat, it does help to explain the feeling, current among critics, that the music has lost its creative drive. Few writers have a kind word for any of the most popular bands of the Seventies, apart from such cerebral favorites as Steely Dan and Roxy Music. If they listen at all, it's only to grimace at the studied commercial moves, or to reprimand the empty world view a song like "Listen to the Music" seems to represent.

Still, corn-belt boogie has its fans and they number in the millions. To take three timely examples, consider ZZ Top, Bachman-Turner Overdrive and the Doobie Brothers. Stylistic differences apart, these bands have in common a large concert following, particularly in the Midwest, and an ability to sell albums (BTO has had two, and the Doobies three LPs go platinum, selling one million units plus). The two facts are not unrelated: In the crowded marketplace of the Seventies, the surest way to build a band's popularity is to hit the road whenever a new album is released and push for an AM hit. BTO and the Doobies both play the game with consummate skill.

Odd band out in this trio is ZZ Top, a power blues band from Texas that is still building to the superstar status of BTO and the Doobies. Their third LP, Tres Hombres, surprised everyone by hanging on the charts for a year and a half, and eventually going gold (selling more than 500,000 units) and this from a pedestrian trio of musicians playing the most bare-boned variety of boozy blues imaginable. Fandango, their newest offering, includes one side of live material that makes their success all the more inexplicable, by featuring nine minutes of tomfoolery titled "Backdoor Medley," wherein the band simulates burping cows (which may not be so odd: An automotive executive recently claimed that belching cattle are a major source of air pollution).

The ZZ formula runs something like this: Take a B.B. King blues lick, speed it up and amplify to a dull roar, overdub a gruff vocal and then garnish with a touch of maracas, tambourine or hand clapping. The percussive sweetening is this band's distinctive contribution to the genre, but even that is a move borrowed from Andrew Oldham's production of the early Rolling Stones (just list