Although it took in a wide spectrum of sounds and shapes, "progressive rock" in the late '60s and early'70s was, basically, rock that, well, progressed -- from basic blues- and R&B-based guitar pop to a many-sided hybrid that took in elements of jazz, English folk and classical. This hybrid stretched the boundaries of what was a rock 'n' roll song.

It's gone now, most of it -- or at least far less popular than it was.

How very odd, then, that one of the best prog-rock shows I've ever heard -- and, Lord help me, I spent my fair share of time listening to Jethro Tull, Frank Zappa, Yes, Genesis, and the like way back when -- comes in late 1997 in a club in Texas.

Space Opera, which in the early '70s was the hot Cowtown rock 'n' roll band, dusted off the form and a mixture of tunes old and new for a standing-room-only Caravan of Dreams audience last night. And darned if this show (the band's first since the summer of 1980) wasn't a thoroughly enjoyable, friendly and sometimes musically stunning evening.

Where else, after all, could one hear lovely original Beatlesesque pop songs rub shoulders with the passages from Frank Zappa's Absolutely Free, Stravinsky's ballet Pulcinella, the ancient Scotch/Irish Ballad Awake, Awake, and knotty instrumental flourishes reminiscent of prime Yes or Tull?

Nowhere. Not in 1997 and, in all probability, nowhere else in 1972, either. That year is when guitarists/vocalists David Bullock and Scott Fraser, bassist Philip White and drummer Brett Wilson were headlining local shows and opening for major acts such as Jefferson Airplane.

Last night the bank -- and especially Bullock's lead vocals and the Bullock/Fraser/White harmonies -- sounded wonderfully fresh and tight. And adding underpinnings of keyboardist Jeff Ward and multi-instrumentalist William Jackson (who spent much of this time on clarinet), all of the songs above and old original tunes such as Singers & Sailors, Riddle and Blue Ridge Mountains came across beautifully.

Because this show was structured as one long piece of music -- with few breaks for applause, band introductions and changing instruments -- it had an invigorating flow and shape. The hardish rock of Singers eased into Awake, Awake, which in turn melted into a spritely new Bullock song, Vieux Carre. That, in turn, with only a moment's rest, turned into the band's cover of the Beatles' ultra-rare (and never officially released) L.S. Bumblebee. And so on.

The balance of the familiar with the new, and trickier instrumental passages with sweet, affecting songs such as Bullock's Fly Away, Fraser's Stolen Ground, and White's Fly Away, was just right. And because the set as a whole was arranged so well, the long passages never felt daunting.

Moving from mood to mood and using subtle shadings of everything from six- and 12-string guitars to oboe, accordion and the ancient viola da gamba, Space Opera lived up to its legend and pointed the way to a fresh new start.

Along the way they made me feel a whole lot better about all those Jethro Tull albums gathering dust back at my parents' house.