Van Morrison was working through one of his greatest -- yet least appreciated -- creative periods when he made this album, one that burrows deeply into an introspective jazz-rooted spiritual groove.

With Mark Isham's lonely muted trumpet up front, listeners are in the jazz world immediately with "Haunts of Ancient Peace," merging perfectly with Morrison's idiosyncratic vocal style.

A low-pressure soul-jazz organ riff lays down the base of the most easily assimilated track, "Satisfied," as Morrison's lyric indicates that he has reached a state of internal peace.

"Wild Honey" has R&B horn riffs over Philly-style strings, while "Spirit" mostly pursues a self-fulfillment path similar to that of "Satisfied." Ultimately, the record stands or falls upon two remarkable, gigantic 15-minute pieces, "Summertime in England" and "When Heart Is Open." The propulsive opening of "Summertime" drops names of Morrison's favorite poets and authors; the track teeters upon indulgence but you are drawn in by Morrison's obsessions with lines and phrases like "common one" and "let your red robe go," his voice becoming a twin brother of arranger Pee Wee Ellis' riffing sax.

Lonely horns over the hilltops open "When Heart Is Open," and it begins to resemble a sequel to Miles Davis' treatment of "In a Silent Way," setting a peaceful, mesmerizing mood that carries you through its enormous length to the end of the record.

No wonder the rock critics of the time didn't get it; this is music outside the pop mainstream, and even Morrison's own earlier musical territory.

But it retains its trancelike power to this day.