Considering Fleetwood Mac’s enormous popularity in the 1970s, which can be traced to the moment Lindsey Buckingham and Stevie Nicks joined the waning band, Buckingham would have to rank as one of the most underrated guitarists in rock. He is also one of the more unorthodox.

An ex-folkie who displays his acoustic fingerpicking on “Landslide” and “World Turning” from the group’s self-titled 1975 comeback, Buckingham’s “technique” on electric lead was closer to clawhammer banjo – flailing away with pickless fingers, which usually ended up bloody by the end of a set. But his sensibility was best exhibited on “I’m So Afraid,” from the same album, which became his extended showstopper onstage. The licks were simple, but with Lindsey’s sense of dynamics (and a super-long setting on his delay), the effect was mesmerizing.

By the time of Tusk, in 1979, Mac’s triple threat of singer/songwriters was still in place, but Buckingham had become the album’s (and band’s) clear visionary. When critics compared the double album to the Beatles’ “White Album,” which signaled the Fab Four working as four solo artists backing each other more than the work of a unified quartet, Buckingham replied, “I like the ‘White Album.’ I consider that a compliment.”

Like the “White Album,” Tusk jumps all over the map, stylistically and sonically, with a conscious disregard for continuity. It was anything but a logical followup to Rumours‘ mega-success – which was, of course, the whole point.

Nicks continued to represent the band’s mystical bent, while McVie contributed more love songs. But feeling the influence of the burgeoning new wave scene, Buckingham’s stance is more aggressive, the rhythms heavier-handed, his guitar lines more jagged, its tone more squawky. And his solo on Stevie’s “Sisters Of The Moon” is among his most impassioned.

Again, the second disc of this double-set is mostly alternate takes and demos of the same material, but a couple of non-originals that didn’t make the album are of special interest. “Kiss And Run” was written by Jorge Calderon (who recently won a Grammy for co-producing Warren Zevon’s final album, The Wind), and the Beach Boys’ “Farmer’s Daughter” would turn up on 1980’s Fleetwood Mac Live.

If Tusk was merely an exercise in self-indulgence in the wake of mass appeal, it would be understandable. But, like its title song (featuring the USC Trojan Marching Band), it’s more adventurous than that, and, in any case, a bold artistic statement.