Mastodon’s past flirtations with prog have consistently pitched toward the metal side of scrimmage, never fully embracing the melodic pomp of Yes and ELP. Crack The Skye—though still intrinsically a metal album—is rife with unabashed overtures to the symphonic rock of yore. The mosaic’s central tile is “The Czar,” a four-part ode to Rasputin bursting with Moog lines and Eastern European folk. “Ghost of Karelia” briefly doffs the fox mask to revisit the band’s signature style—double-bass drums and tuneful hooks welded to inscrutable libretto: “Wrathful ones, nine eyes gaze / Holding skulls / Filled and laced / With human blood.” Yet the most progressive part of the album is the band’s restrained temperament. Amidst blistering tritone riffs and arpeggiated chords is a group keener to explore sonic harmony than crank the distortion. Crack the Skye is an epic trek across the space-time continuum, entirely on Mastodon’s terms.