For a half generation of jazz fans--those who came of age to the music of John Coltrane--there remains something almost mystical about Elvin Jones, who authored the apocalyptic pulse at the heart of Coltrane's quartet. Jones was the drummer who took the beat which had previously occupied several discrete parts of the drum set, and spread it out to the entire instrument; that concept, along with a resilient creativity and almost scary energy, defines his style. Most drummers can't be this powerful without overwhelming the other musicians on stage, but Jones--like Art Blakey, Max Roach, and only a few others--takes it to the next level: his dark, irrepressible earth rhythms enhance the contributions of his sidemen. (Take for example pianist James Williams, who has performed in various other contexts in Chicago, but who's sounded that much better this week.) I suppose that for Jones's sidemen, playing with him is akin to riding the tiger, where the only way to avoid disaster is to stay on top of it. Jones's Chicago visit was to have been a two-saxophone affair, but altoist Sonny Fortune didn't make the trip; in his stead, trumpeter Wallace Roney shares the front line with the muscular tenor of Pat LaBarbara. The superb bassist Chip Jackson rounds out the quintet, offering time strong enough to lead almost any other drummer. Tonight and Saturday, 9 and 11 PM, and Sunday, 4, 8, and 10 PM, Joe Segal's Jazz Showcase, Blackstone Hotel, 636 S. Michigan; 427-4300.