MONT DE MARSAN, an arrondissement of the department of Les Landes, in France, 2180 square miles in extent. It contains twelve cantons, which are divided into 136 communes, and a population of about 83,000 persons. The capital is a city of the same name, situated at the junction of the rivers Midou and Douze, which, united, run to the Adour. It contains 4200 inhabitants, who subsist by trading in the few productions of the soil. Long. 0. 49. W. Lat. 44. 0. N.