# 1911 Encyclopædia Britannica/Dolomieu, Déodat Guy Silvain Tancrède Gratet de

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​DOLOMIEU, DÉODAT GUY SILVAIN TANCRÈDE GRATET DE (1750–1801), French geologist and mineralogist, was born at Dolomieu, near Tour-du-Pin, in the department of Isère in France, on the 24th of June 1750. He was admitted in his infancy a member of the Order of Malta. In his nineteenth year he quarrelled with a knight of the galley on which he was serving, and in the duel that ensued killed him. He was condemned to death for his crime, but in consideration of his youth the grand master granted him a pardon, which, at the instance of Cardinal Torrigiani, was confirmed by Pope Clement XIII., and after nine months’ imprisonment he was set at liberty. Throughout that period he had solaced himself with the study of the physical sciences, and during his subsequent residence at Metz he continued to devote himself to them. In 1775 he published his Recherches sur la pesanteur des corps à differentes distances du centre de la terre, and two Italian translations of mineralogical treatises by A. F. Cronstedt (1702–1765) and T. O. Bergman (1735–1784). These works gained for him the honour of election as a corresponding member of the Académie des Sciences at Paris. To obtain leisure to follow his favourite pursuits Dolomieu now threw up the commission which, since the age of fifteen, he had held in the carabineers, and in 1777 he accompanied the bailli (afterwards Cardinal L. R. E.) de Rohan to Portugal. In the following year he visited Spain, and in 1780 and 1781 Sicily and the adjacent islands. Two months of the year 1782 were spent in examining the geological structure of the Pyrenees, and in 1783 the earthquake of Calabria induced him to go to Italy. The scientific results of these excursions are given in his Voyage aux îles de Lipari (1783); Mémoire sur le tremblement de terre de la Calabre (1784); Mémoire sur les îles Ponces, et catalogue raisonné des produits de l’Etna (1788) and other works. In 1789 and 1790 he busied himself with an examination of the Alps, his observations on which form the subject of numerous memoirs published in the Journal de physique. The mineral dolomite, which was named after him, was described by Dolomieu in 1791. He returned to France in that year, bringing with him rich collections of minerals. On the 14th of September 1792 the duc de la Rochefoucauld, with whom he had been for twenty years on terms of the closest intimacy, was assassinated at Forges, and Dolomieu retired with the widow and daughter of the duke to their estate of Roche Guyon, where he wrote several important scientific papers. The events of the 9th Thermidor (July 27, 1794) having restored the country to some tranquillity, Dolomieu recommenced his geological tours, and visited various parts of France with which he had been previously unacquainted. He was in 1796 appointed engineer and professor at the school of mines, and was chosen a member of the Institute at the time of its formation. At the end of 1797 he joined the scientific staff which in 1798 accompanied Bonaparte’s expedition to Egypt. He had proceeded up the Nile as far as Cairo when ill-health made his return to Europe necessary, and on the 7th of March 1799 he set sail from Alexandria. His ship proving unseaworthy put into Taranto, and as Naples was then at war with France, all the French passengers were made prisoners. On the 22nd of May they were carried by ship to Messina, whence, with the exception of Dolomieu, they embarked for the coast of France. Dolomieu had been an object of the hatred of the Neapolitan court since 1783, when he revealed to the grand master of his order its designs against Malta, and the calumnies of his enemies on that island served now as a pretext for his detention. He was confined in a pestilential dungeon, where, clothed in rags, and having nothing but a little straw for a bed, he languished during twenty-one months. Dolomieu, however, did not abandon himself to despair. Deprived of writing materials, he made a piece of wood his pen, and with the smoke of his lamp for ink he wrote upon the margins of a Bible, the only book he still possessed, his treatise Sur la philosophie minéralogique et sur l’espèce minérale (1801). Friends entreated, but in vain, for his liberty; it was with difficulty that they succeeded in furnishing him with a little assistance, and it was only by virtue of a special clause in the treaty between France and Naples that, on the 15th of March 1801, he was released. On his arrival in France he commenced the duties of the chair of mineralogy at the museum ​of natural history, to which, after the death of Daubenton, he had been elected in January 1800. His course of lectures concluded, he revisited Switzerland. Returning thence he reached the residence of his brother-in-law at Château-Neuf, in the department of Saône-et-Loire, where he was seized with a fever, to which in a few days he succumbed, on the 26th of November 1801.
Dolomieu’s geological theories are remarkable for originality and boldness of conception. The materials constituting the primordial globe he held to have arranged themselves according to their specific gravities, so as to have constituted a fluid central sphere, a solid crust external to this, next a stratum of water, and lastly the atmosphere. Where water penetrated through the crust, solidification took place in the underlying fluid mass, which enlarging in consequence produced rifts in the superincumbent rocks. Water rushing down through the rifts became decomposed, and the resulting effervescence occasioned submarine volcanoes. The crust of the earth he believed to be continually increasing in thickness, owing to the deposition of aqueous rocks, and to the gradual solidification of the molten interior, so that the volcanic eruptions and other geological phenomena of former must have been of far greater magnitude and frequency than those of recent times.
See Lacépède, “Éloge historique de Dolomieu,” in Mémoires de la classe des sciences de l’Institut (1806); Thomson, in Annals of Philosophy, vol. xii. p. 161 (1808).