A Black Marble Striking Calendar Mantel Clock, signed Potonie Leon, Paris, circa 1870, the black

A Black Marble Striking Calendar Mantel Clock, signed Potonie Leon, Paris, circa 1870, the black marble case with flat top and a wavy shaped base, 5-inch rectangular dial with engraved foliate decoration, white enamel Roman chapter ring with slow/fast adjustment at 12, with visible Brocot escapement to the recessed white enamel centre, subsidiary dials for day and date, twin barrel movement with countwheel striking on bell, dial and movement signed, 31cm high