Mastodon, "Crack the Skye" (Warner Bros.) [3.5 STARS]

The problem with a lot of the so-called “prog-metal” genre is that the bands either skimp on the unrelenting bottom of great metal in their effort to be pointlessly complex and “progressive,” or the invention and melody of great progressive-rock is barely discernable amid the thunderous metal assault. The Atlanta quartet Mastodon gets it right on both counts, and on its eagerly anticipated fourth studio album, it also adds a wonderfully dark and disorienting psychedelic swirl (a la vintage Hawkwind) and an even more ambitious conceptual construct than on its 2004 epic “Leviathan” (nominally inspired by Melville’s Great White Whale).

The story is graphic-novel gonzo, involving a crippled young man who projects himself into an alternate universe via astral travel and meets up with Rasputin, though as drummer Brann Dailor told Billboard, “It’s all metaphors for personal s–t.” As focused as the lyrics are obtuse, the concise, powerful production of Brendan O’Brien (Pearl Jam, Stone Temple Pilots, Rage Against the Machine) keeps things firmly rooted in the requisite dinosaur thump even as the vocals acquire a new melodic edge (relatively speaking) and the guitars veer off into the psychedelic stratosphere in a way that suggests that Mastodon is only beginning to come into its own and show us what it’s really capable of.