A decade later he moved on to the École des Mines where he served as director from 1872. Dubrée studied the origins, formation and composition of rock, metamorphism and the classification of meteorites. - In view of Dubrée's career at the Muséum the letter can be dated between 1861 and 1871. As he mentions an appointment at "l'Exposition" it is likely that the visit took place during the Paris "Exposition Universelle" of 1867. - On stationery with embossed monogram in gold; mounted in collector's folder..