Forgery
The base stamp is a forgery.
This overprint was used often by Fournier.
For info on the forgery look HERE
Bibliography
The Work of Jean De Sperati by the British Philatelic Association 1955
Album Weeds by Rev. R. B. Earee
The Serrane Guide by Fernand Serrane
The Forged Stamps of all Countries by J. Dorn