Less a sweeping love story and more of a heads-up not to bang the interns, "Ammonite" works well enough when Winslet's isolated fossil hunter is front and center — with writer-director Francis Lee painting a tragic portrait of a woman caught between her studious craft and passionate love life — but heavy-handed metaphors stack up faster than rocks on a beach, and the typically magnetic Ronan can't find her footing in a story that works better without her.