The San Francisco sound of the '60s made a distinctive and significant contribution to rock music as a developing art. It began simply as folk themes put to rock beats and evolved into music which was highly political in both lyric content and artistic stance. Groups donned a collective persona of iconoclasm, denouncing The Establishment while publicly participating in drugs and free sex, and generally languishing in libido liberation.

The music was characterized by distortion, feedback and fuzz tone intended to simulate the effect of mind-expanding drugs. Open-ended and improvisational in structure, the music experimented with time, freely extending and/or telescoping a piece against a kaleidoscopic light show, meant to mirror the visual transports of an LSD trip.

This was so-called acid or psychedelic rock, and the groups experimenting in these musical (and pharmaceutical) excesses were the Jefferson Airplane, the Grateful Dead, Big Brother and the Holding Company, Quicksilver Messenger Service and Blue Cheer, to name the core. If San Francisco was, as some critics have claimed, the "Liverpool of the U.S.A.," then the Jefferson Airplane were the Beatles, defining and honing that sound to a razor-edge clarity.

The Airplane's trip, however, ended not with a bang, but a whimper when Marty Balin, the group's original leader, left in 1971, and other members made forays into the rock scene on their own or in pairs - splitting the creative force behind the Airplane.

Grace Slick and Paul Kantner took flight again in 1974, this time on a Starship, and Marty Balin rejoined the next year. Their first three albums, "Dragonfly," "Red Octopus" and "Spitfire," while selling well, were uneven; they experienced some in-flight turbulence. The Jefferson Starship's latest release, "Earth" (Grunt-BXL1-2515), however, follows a steady trajectory.

The Starship's sound, while less psychedelic than the Airplane's '60s sound (not as free-ranging, no longer distorted with heavy feedback) still has an unmistakable Airplane/Starship quality to it. That in part has to do with their harmonies, which are most often minor chords or major 7ths and added 6ths, frequently in an open position (that is, the notes of the chord widely spaced). It is not unusual for them to improvise freely, vocally and instrumentally, around a single chord with no modulation, creating a sense of non-resolution, an open-ended harmonic and melodic structure.

This lack of harmonic gravitation is most notable on "Love Too Good," "Count On Me" (where the resolution from A major to E major is the reverse of what we would normally expect), "Take Your Time," "Skate-board," "Fire" and "Show Yourself."

Three songs - "Crazy Feelin'," "Runaway" and "All Nite Long" - seem to borrow from the successful sound of Fleetwood Mac. Although in "All Nite Long," what begins as Fleetwood Mac-like tight harmony, full sound and neat modulations moves into unbridled improvisation, impressive for Grace Slick's energetic vocal variations on a single theme.

Although Slick is not spotlighted on this song as she is on "Love Too Good," "Take Your Time," "Skate-board" and "Show Yourself," it is definitely her song. And the album is her album. She is featured on four of the nine songs (as compared to two of nine on "Spitfire").

"Skateboard" is the song most similar to the old Grace Slick and the Jefferson Airplane. There is a surrealistic, other-wordly tonal quality as the Starship careens around and around the same note with Slick on lead vocal sliding and maneuvering her way to the notes like a hockey forward maneuvering his puck into position for the goal.

But the tour de force of this album is "Take Your Time," lyrics and music by Slick and sung by her. It's a song about commitment and personal differences in the timing of a relationship. Slick wails:

Take your time

Take your time

And I'll take my own time.

The problem is to get the two timings to work out at the same time.

You say it'll take a year

I say just take me a second

But there's room for both of us

Just open the room

You know a year of time sees so

Many changes

And the speed of light in the black

Makes a full moon . . .

THe paradox ends the song by suggesting a future resolution to the temporal conflict, and the music trails off, reinforcing that suggestion.