For their follow-up to 2004’s Leviathan — a masterful prog-metal concept album based on Herman Melville’s Moby-Dick, which helped them poke out of the underground — Atlanta’s Mastodon hit the books even harder, embracing Howard Bloom’s The Lucifer Principle, an esoteric tome that posits that man’s capacity for evil dwells in his vestigial “reptile brain.” Lucifer inspires a fantastical narrative in which a protagonist scales a mountain populated by malevolent tree beings (dude!) and furry man-beasts (sweet!). Problem is, Blood Mountain’s hail of convoluted riffs and abrupt time-signature changes never settles into one of Leviathan’s mammoth grooves, and the maelstrom all but consumes cameos by Queens of the Stone Age mainman Josh Homme and Mars Volta vocalist Cedric Bixler-Zavala. Listeners looking for a memorable melody would have better luck tracking a great white whale across the seven seas.

Download: “Crystal Skull,” “Pendulous Skin”