analyses, eruptive masses of the most varied kind, the knowledge derived from which threw light upon the principles of science, from granites and syenites to melaphyres and basalts. After thirty years of study and progress, other _savants_, without differing from him, progressed further in the intimate knowledge of rocks; but the historian of science will not forget that Delesse was the precursor of this order of research. His studies of metamorphism will long do him honor. The mineralogical modifications which the eruptive rocks have undergone in the mass are the permanent witnesses which attracted all his attention. The chemical comparison of the metamorphic with the normal rock pointed out distinctly the nature of the substances acquired or lost. One of the principal results of these analyses has been to lessen the importance attributed until then to heat alone, and to show in more than one case the intervention of thermal sources and of other emanations from below, to which the eruptive rocks have simply opened up tracks. It is not only upon subjects relating to the history of rocks that Delesse has touched. Witness his work on the infiltration of water, as well as his volume relating to the materials of construction, published on the occasion of the Exhibition of 1855. The nature of the deposits which operate continually at the bottom of the sea offers points of interest which well repay the labor of the geologist. He finds there, indeed, a precious field to be compared with stratified deposits; for in spite of the enormous depth to which they form a part of continents, they are of analogous origin. Delesse laboriously studied the products of the innumerable soundings taken in most of the seas. He arranged the results in a work which has become classical with the beautiful atlas of submarine drawings which accompany it. Though he never slackened in his own especial work, he made much of the work of others. The "Revue des Progrès de la Géologie," with which he enriched the "Annales des Mines" for twenty years, would have been sufficient to engross the time of a less active scientific man, and one less ready to grasp the opening of a discovery. This indefatigable theorist never neglected the applications of science: the nature and the changes of the layers which form the under earth; the course and the depth of the subterraneous sheets of water; the mineralogical composition of the earth's vegetation, were represented by him on several charts and plans drawn out in proper form. His maps which follow the route of many of the great French lines of railway explain the kind of soil upon which they are laid, and are of daily use. In the pursuit of his numerous scientific works, Delesse never failed in discharging his duties in the Corps des Mines. Having in 1864 quitted the service of the Government of Paris, which he had occupied for eighteen years, he was made professor of agriculture, of