When you were young you probably had pals who were much, much smarter than you. You know, the guys who were discussing the space/time paradigm and divining water in the back garden while you, in contrast, were attempting to divine other things with the assistance of a mangled copy of Fiesta. Atlanta's Mastodon, in comparison to their peers, are like those mates, and their fourth offering is frankly like taking a trip into progressive rock hyperspace. You might assume that to achieve such an act of time and space travel would involve a frantic, forced and overblown effort. But this is as laid back and confident as you'll ever lay ears on, and completely unlike anything around today's sonic solar system. Given the somewhat trying circumstances under which it evolved, this is of great testament to Mastodon's tenacity.

Prog has unfortunately become synonymous with over-complicated and unnecessarily corpulent noodling. If, however, you want to hear the most intelligent, relevant form of genuinely advancing rock music this side of Valhalla you'd do a lot worse set up an encounter with Crack The Skye.

Opener 'Oblivion' creeps out of some ancient ice cave, its initial menace-encrusted tones demanding both your immediate attention and vastly increased volume before settling into an angular crunch completely founded on Brann Dailor's drum fills, reminiscent of Rush's own Neil Peart. All this before shifting seamlessly to a chorus that's pure Soundgarden.Then, just when you think you've got this all figured out they throw in a freaky, Eastern sounding ukulele intro to 'Divinations' which then calmly teleports itself into a dizzying vista of circular, folk-like riffscape but with a somehow new-age feel to it, leaving you thinking ' huh' ?

No wonder you're confused, and it doesn't exactly get any more straightforward either, 'cos the meat of the record is jointly its most ambitious and most unexpected twist. In most instances nowadays, to even contemplate producing a song divided into four 'acts' represents commercial and reputational suicide. To then throw in lyrics about Czarist Russia and expect to still be a functioning band the next week demands a level of self-assurance that not many of us possess.

Fortunately for them and us the listener, Mastodon are more than up to that challenge because 'TheCzar (Usurper/Escape/Martyr/Spiral)' is the album's backbone. The great slew of styles is heralded by the mammoth riff that starts the second 'act', and iced perfectly by the laid back grandeur of 'Spiral' with its classic rock guitar solo. It gets better too, twice in fact. 'Ghost of Karelia' is the closest thing you'll find here to an obvious single, although you'd suspect Mastodon don't DO singles. It's delicately picked intro lulls you quietly into another wickedly jagged riff and more of that staccato sticksmithery from Dailor, who you now suspect is loving this outing like a prehistoric pig in the proverbial.

Prepare to chisel yourself off the ceiling though, because closer 'The Last Baron' is jaw-dropping, every bit of its 13-minute duration. Sounding like Ozzy, with the opening line “I guess they can say, we can set the world ablaze”..Brent Hinds instantly convinces you (a) that this band probably can and (b) that modern rock/metal may be about to undergo wholesale change, and one that is so very welcome.

To engage the services of someone with such overtly 'commercial' pedigree as Brendan O'Brien behind the desk of doom should really have tipped us off as to what plan Mastodon had in mind here. The overall sound is a given: it's huge. More impressive, however, is the statement therein: in effect it's saying that to make technically innovative heavy music within a forum of mass appeal is acceptable and better still, genuinely invigorating, hammering another large gnarly nail into the coffin of what we used to think progressive was all about. More are required...