Etienne Jules Adolphe Desmier de Saint-Simon, Vicomte d'Archiac (September 24, 1802 - December 24, 1868), was a French geologist and paleontologist.

He was born at Reims and educated in the Military School of St Cyr, and served for nine years as a cavalry officer until 1830, when he retired from the service. Prior to this he had published an historical romance; but now geology came to occupy his chief attention. In his earlier scientific works, which date from 1835, described the Tertiary and Cretaceous formations of France, Belgium and England, and dealt especially with the distribution of fossils geographically and in sequence. Later on he investigated the Carboniferous, Devonian and Silurian formations.

His great work was Histoire des Progrès de la Géologie de 1834 a 1859, published in 8 volumes (1847-1860). In 1853 the Wollaston Medal of the Geological Society of London was awarded to him. In the same year, with Jules Haime (1824-1856), he published a monograph on the Nummulitic formation of India. In 1857 was elected a member of the French Academy of Sciences, and in 1851 he was appointed professor of paleontology in the Muséum National d'Histoire Naturelle in Paris. Of later works his Paléontologie Stratigraphique, in 3 vols. (1864-1865); his Géologie et paléontologie (1866); and his paleontological contributions to de Tchihatcheff's Asie mineure (1866), may be specially mentioned. While suffering from severe depression he committed suicide by throwing himself into the River Seine on Christmas Eve, 1868.