Slate Wall Sundial, Engraved Lion, 19thc Mastery Work

328699 Large slate dial, square shape with cut sides, the edge deeply molded. Very fine engraving of a sundial from 4h to 20h, in the center: a crescent moon, hourly figures very finely drawn, half-hours marked by arrows. Below, naively engraved, the silhouette of a Lion, (for the city of LYON?), And signed with a floret: "for Mr Montaseau". No preparation of slate to receive a gnomon, which makes me think that this dial is an engraving exercise rather than a real sundial, (which would be engraved much deeper), maybe it is a work of mastery under the direction of Mr Montaseau? ....
Difficult to date, the molding, figures and letters are engraved in the style of the 18thc, but it is probably a work circa 1830
dimensions: 33 x 33cm.
Condition is good. No flaw, apart from edge chips and a little wear on the surface. I powdered the face of white to shaw quality of engraving.