Oregonian heavy metal iconoclasts Agalloch have rarely sat still, creatively speaking, over the course of their celebrated career, and yet there's a distinct back-to-basics feel about the group's oftentimes familiar-sounding fourth full-length opus, 2010's Marrow of the Spirit.

Mind you, this doesn't result from the album having been been recorded and mixed strictly on analog equipment (making it somewhat less than pristine, yet intentionally so, in the production department), but rather because the music heard on Marrow of the Spirit feels like something of a stylistic omnibus, covering many of the radically different chapters visited individually by the band's prior discography.

Surely almost no one expected Agalloch to dive into the black metal abyss ever again, never mind as lustily as they do on "Into the Painted Grey," which may actually be the group's most vicious composition ever.

But far from settling for uniformity, this 12-minute epic (preceded by a solo cello piece performed by Garyceon's Jackie Perez Gratz) still makes room for sublime melodies and calmer moods amid its coarse riffs and scything blastbeats, and is then followed by a more restrained and eerie folk-metal journey called "The Watcher's Monolith," which is actually quite reminiscent of Agalloch's 2002 landmark The Mantle.

Not that fans will mind that one bit -- certainly not once the momentous, truly groundbreaking "Black Lake Niðstång" begins to unfold, covering 17 minutes' worth of distinct but interlocking sonic vistas of breathtaking imagination, from its dreamy atmospherics through its doom-like drones to its cathartic metallic finale.

As things turn out, this artistic high point is also impossible to top, even though Agalloch deliver a pair of additional stunners in "Ghosts of the Midwinter Fires" (an insistently paced gothic rocker built on Echoplexing plucked guitar lines) and "To Drown" (characterized by a somber minimalism and melancholy chorused guitars snaking around yet another evocative cello performance).

Rounding out this album's aforementioned anthologizing character, these last two movements occasionally draw parallels with 2006's darkwave-infused Ashes Against the Grain and even 2008's magnificent Wickerman folk homage, The White EP, but to call it repetition would not do them justice.

Instead, Marrow of the Spirit merely reflects a mature Agalloch, taking stock of a decade's worth of peerlessly pioneering extreme metal, before forging ahead into further worlds unknown.