I’m not sure what the construction at the bottom of this tracing board is supposed to be. It looks like a tunnel. This is the tracing board of the “Vray Maitre et Ecossais” (‘true master and Scot’) degree which is supposedly from 1745.
The degree also appears to be called “Écossais de la Voûte Sacrée” or ‘Schot of the sacred vault’, so it just might be a somewhat uncommon version of the Royal Arch, or at least, the vault in which Royal Arch masons find the Word.
Also see: cold man
Bibliotheque Nationale de France – Fonds Maçonnique – FM4 (232)