With Shamrock City the Philadelphia-based Solas turns from the electrified Irish-flavored roots music of its recent albums to the acoustic sound of its early releases. It's an ambitious project: an attempt to tell the story of the Irish immigrants who worked the hellhole that was "the richest hill on earth," the copper mines of Butte, Montana. Anyone who knows something of that history, or has simply heard some of the songs the late Utah Phillips wrote on the subject, knows this is a grim tale defined by unregulated capitalism and brutal exploitation.

Fortunately, though often mournful, Shamrock City is in no sense off-putting. It's even high-spirited at times when it's creating its version of the good-time music of Irish-American laborers in the American West at the turn of the last century. The proximate inspiration, however, is a specific tragedy, the fate of one Michael Conway, Solas member Seamus Egan's great-great uncle, who was beaten to death when he ran afoul of Butte's corrupt police force. The album grew up around the aptly titled ballad "Michael Conway," which Eagan wrote with another Solas stalwart, Mick McAuley.

Perhaps unsurprisingly, the music is uniformly strong -- not always the case with themed albums, on which the requirements of storytelling sometimes get in the way of compelling melody. As it should, each cut, song or instrumental, manages to stand comfortably on its own. With rare exception these are originals, albeit in-the-tradition ones performed by a band whose immersion in the old music is documented across a long career.

Solas invites some distinguished guests, among them the Scottish balladeer/activist Dick Gaughan (who sings lead on the hard-hitting "Labour Song"), the Carolina Chocolate Drops' Rhiannon Giddens, Crooked Still's Aoife O'Donovan and more, who fall into the proceedings as organically as if they'd been there all along. Solas regulars Winifred Horan (fiddle), Eamon McElholm (multiple instruments) and Niamh Varian-Barry are at the top of the current generation Irish-American musicians, their very names attesting to the band's authenticity.

Shamrock City ends on a note of tough-minded, unsentimental triumph, or at least survival, with McAuley-Eagan's "No Forgotten Man," though not before taking us through hard times and cruel circumstances made bearable by faith and determination, not to mention alcohol and sex. In a lifetime of listening to folk music, I am often struck at how the worst human experiences so often make for the most enduring music. It's a lesson Solas has taken to heart on this CD of lovely songs and tunes celebrating battered but not broken spirits.