‘Ammonite’ derives its muted shine from Kate Winslet and Saoirse Ronan

“Ammonite” joins a long list of forbidden love stories, yielding a movie presented in washed-out tones, which shines principally thanks to Kate Winslet and Saoirse Ronan. The result is a slow-moving, somewhat predictable but finally effective period romance that primarily serves as an old-fashioned testament to star power.

Set in the 1840s, the film features Winslet as Mary Anning, an accomplished fossil hunter who plies her trade along the English coastline, selling her discoveries to tourists. Living with her mother (Gemma Jones), she’s basically sleepwalking through her hardscrabble existence, other than her work, when she meets Ronan’s Charlotte, a wealthy woman afflicted by what her husband unhelpfully describes as “mild melancholia.”

Said husband (James McArdle) has developed an interest in fossils himself, and after seeking her advice, asks Mary to essentially babysit his bride while he goes off to explore. Resistant at first, Mary — who harbors her own painful past — is increasingly drawn to her charge, as the two awaken the spark in each other.

Written and directed by Francis Lee (“God’s Own Country”), it’s frankly hard to describe “Ammonite” (a reference to the extinct, shelled creatures found embedded in the rocks) without making the movie sound as derivative as it is. The performances, however, elevate the material, as Winslet and Ronan each convey grappling with different kinds of trauma without speaking about what ails them.

When they finally do connect — after what feels like a too-long buildup — those scenes are raw and passionate. Inevitably, they’re also tinged with sadness, given that Charlotte has a home to which she seemingly must return, offering little chance of enduring happiness. Last year’s “Portrait of a Lady on Fire” (set about 70 years earlier) and the HBO series “Gentleman Jack” come to mind as recent examples that similarly filter the LGBTQ experience through the intolerance of the era.

Winslet and Ronan are no strangers to period fare, including Ronan’s star turn in last year’s “Little Women.” Yet the quiet desperation of the former’s character perhaps most closely resembles her role in “Little Children,” another story in which a seemingly hopeless affair carried a fleeting sense of elation.

Pivoting to the hunt for more pragmatic treasures, it’s worth noting that Winslet has already collected seven Oscar nominations. Despite being a small-boned movie, in this very strange year it wouldn’t be a surprise if “Ammonite” lets her unearth another.

“Ammonite” premieres in select theaters on Nov. 13 and premium on demand on Dec. 4. It’s rated R.