Dolomieu, Dieudonné (Called D

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Dolomieu, Dieudonné (Called DéODAT) DEGRATET DE

(b. Dolomieu, Dauphiné, France, 23 June 1750; d. Châteauneuf, Saône-et-Loire, France, 28 [16? 29?] November 1801)

geology.

One of eleven children of François de Gratet, marquis de Dolomieu, and of Marie-Françoise de Bérenger, Dolomieu was placed in the Sovereign and Military Order of the Knights of Malta at the age of two. Because of his precocious interest in natural objects, he is supposed to have been sent to Paris for a part of his education before the beginning of his military career. He was a member of the carabiniers in 1764, then served his apprenticeship aboard one of the order’s galleys in 1766, achieving the rank of second lieutenant in the same year. He rose to lieutenant in 1774, became a knight in 1778, was promoted to captain in 1779, and commander in 1780.

His career in the Knights of Malta was marked by a long series of difficulties. In 1768, after a duel in which he killed a fellow member of the order, he was sentenced to life imprisonment but was released through the intervention of Pope Clement XIII. In the early 1780’s he resigned as lieutenant du maréchal of his Langue (Auvergne), following a dispute with the grand master concerning an alleged transgression of the rights of the Langues; he carried on a legal battle for several years thereafter, acquiring some bitter enemies within the order. He finally left Malta in 1791, and his expression of pro-Revolutionary opinion soon began to elicit accusations of his involvement in a plot to destroy the order—which did indeed suffer grave setbacks during the Revolution. Dolomieu eventually played an unwilling role in Napoleon’s seizure of Malta in 1798.

Garrisoned in Metz between 1771 and 1774, Dolomieu began to cultivate science under the tutelage of Jean-Baptiste Thyrion, an apothecary who taught chemistry and physics (and who was the mentor of Jean-François Pilâtre de Rozier as well). Dolomieu became the friend of Duke Louis-Alexandre de La Rochefoucauld, who helped secure Dolomieu’s election as correspondent of the Royal Academy of Sciences in 1778, and whose mother, the duchess d’Enville, was hostess of a salon where Dolomieu met members of the fashionably learned world. La Rochefoucauld, who had made the grand tour in 1765–1766 in the company of Nicolas Desmarest, helped direct Dolomieu’s interests toward mineralogy. In 1775 Dolomieu toured Anjou and Brittany, investigating mines and ironworks and studying the origin of saltpeter. He traveled in the Alps and in Italy in 1776, seeing the region of Vesuvius. His eulogizer Lacépède to the contrary, he probably did not visit Sicily and climb to the summit of Etna.

Dolomieu’s determination to pursue geological science became firm in 1778, when he acted as secretary to Prince Camille de Rohan during an embassy of the order to Portugal, where he studied basaltic rocks. Soon afterward (in 1779 or 1780) he retired from active service with the Knights of Malta and devoted himself to his scientific investigations, although much of his time was taken up in litigation over affairs in the order. He maintained a home in Malta but made frequent journeys for geological and other purposes, traveling in Sicily in 1781, in the Pyrenees (with Philippe-Isidore Picot de Lapeyrouse) in 1782, in Italy and Elba in 1784, Italy and Corsica in 1786, and in the Alps in 1789 and frequently thereafter.

Dolomieu gathered a substantial mineralogical collection, the great bulk of which served him as a pretext for remaining in Malta, despite his ostensible wish to depart because of his political difficulties with the grand master. This collection ultimately became the property of Dolomieu’s brother-in-law, Étienne de Drée, part of it later coming to the Muséum d’Histoire Naturelle.

In 1791 Dolomieu made his way to Paris as a strong partisan of the Revolution, to the consternation of his family and many of his noble associates. In that year he wrote to Picot de Lapeyrouse that he refrained from running for public office only on account of the standing it would cost him with relatives. He joined the Club de 1789 and the Club des Feuillants, and styled himself a constitutional monarchist, a liberal position which the march of events soon made conservative. The excesses of the Revolution—most notably the assassination of his friend La Rochefoucauld in August 1792—repelled him, and he turned against these excesses in public rebuke.

During the hard days that followed, from 1792 through part of 1794, Dolomieu lived at La Roche-Guyon, the La Rochefoucauld château. His relatives were incarcerated or executed and his financial resources wiped out. Dolomieu therefore went to work, entering into a contract with the publisher Panckoucke to write the mineralogical portion of the Encyclopédie méthodique, a project that Dolomieu never completed. In 1794 he was appointed to teach natural history in the Écoles Centrales of Paris, and he was named ingénieur of the Corps des Mines in 1795, which led in 1796 to his assumption of teaching duties in physical geography at the École des Mines. During summer seasons he inspected mines and continued his geological travels in the Alps. When the Academy of Sciences was reconstituted as part of the Institute in 1795, Dolomieu was made a member.

In 1798 Dolomieu joined Napoleon’s expedition to Egypt, during which he was maneuvered into taking part in negotiations for the capitulation of Malta. His stay in Egypt was cut short by illness (and perhaps also by his chagrin at having been used by Napoleon); and on the return voyage to France, when a storm forced his ship to put in at Taranto, he and his companions were imprisoned during the Calabrian counterrevolution. Taken to Messina, Dolomieu fell victim to vindictive influences exercised against him at the court of Naples by some of the Knights of Malta. He suffered a trying solitary imprisonment of twenty-one months until his release in March 1801. His return to Paris marked the end of what had become a cause célèbre among French intellectuals, the unconscionable detention of a scientist on the pretext of reasons of war. Having been elected while in prison to Daubenton’s former chair, Dolomieu began to teach at the Muséum d’Histoire Naturelle; but his health, seriously affected by his ordeal in prison, failed shortly after his last tour in the Alps. He died a bachelor, in accord with his vow as a Knight of Malta, although he had been known to fancy women.

During his relatively brief career Dolomieu acquired a reputation as one of the most astute geologists. This reputation was not attributable to any remarkable theoretical innovation, although Dolomieu was interested in theory and, indeed, possessed greater theoretical commitments than he readily acknowledged. Instead, he was esteemed as a judicious inquirer within the framework of existing styles of geological research, and it is fitting that he is the eponym of a substance—dolomite—and of the Alpine regions largely composed of it, rather than of a geological principle. He was known primarily for his studies of volcanic substances and regions; among his related interests were earthquakes, the structure of mountain ranges, the classification of rocks, and the fashion in which chemical and mineralogical studies could be applied to historical interpretation of the earth.

Dolomieu ascribed his own interest in volcanoes to the influence of Barthélemy Faujas de Saint-Fond, to whom he wrote from Portugal in 1778 concerning his investigation of the origin of basalt. During the 1770’s the new idea that basalt might be of volcanic origin attracted many scientists, especially the French, and Dolomieu rapidly joined the ranks of the adherents of this theory. He accounted for the prismatic form of certain basalts by arguing that they had suffered sudden contraction from the cooling effect of water. His commitment to the proposition that volcanic products are more than casual and accidental creations of the earth, but rather constitute a significant proportion of the earth’s features, is reflected in such descriptive writings as Voyage aux îles de Lipari (1783) and Mémoire sur les îles Ponces (1788), as well as his more analytical papers, most of which were published in Observations sur la physique.

Despite his belief in the historical significance of volcanoes, however, Dolomieu was convinced that aqueous agents were the outstanding causes of geological change. His volcanism was always tempered by this belief. In 1790, at the beginning of the basalt controversy, he declared that “far from extending the empire of subterranean fire, I believe that more than any other [mineralogist] I have circumscribed its true limits and excluded from its domain an infinitude of regions, a multitude of substances that have been attributed to it.”¹ He would not join with those who would make volcanoes responsible for the majority of geological events; to his mind, volcanic effects were limited both spatially and temporally. To be sure, volcanic activity was not an ephemeral event and had occurred repeatedly during various stages of the earth’s history, but by comparison with aqueous agents it was historically an occasional event of inferior significance. He wrote that “the humid way is the most universal means, the oldest, that which acts quietly in all times and all places, to which almost all of our globe belongs, which everywhere reasserts itself and regains possession of that part of its empire... that it yielded momentarily to the dry way.” He estimated that no more than one-twentieth of the entire surface of the earth had ever been affected by volcanic action².

In expounding his doctrine of aqueous geological activity, Dolomieu set forth a historical scheme for the earth that contained many of the components of neptunism. He believed that the oldest rocks had been precipitated out of a universal fluid in the earliest epochs from which there remains any evidence. It was perfectly plausible, he acknowledged, that prior to this coagulation the earth may have experienced a history of undeterminable length, but the absence of remnants from this era prevents our knowing anything about it. The history of the earth begins, for our purposes, with a terraqueous globe and the precipitation of matter from the universal fluid.

Dolomieu reasoned that this fluid cannot have been water alone, since so much matter could not have been dissolved without the aid of some other agent, perhaps a principle of fire or light, such as phlogiston (in 1791 Dolomieu had already noted that this principle was being rejected by chemists, but this did not deter him from positing some like essence). Precipitation out of the primordial solvent must have taken place in reverse order of solubility, in a slow and orderly fashion, and upon its completion the solvent material had largely disappeared. The means of its removal posed a problem; perhaps the atmosphere absorbed it.

The next stage in the geological history proposed by Dolomieu was a series of violent upheavals resulting in the rearrangement of the originally crystallized rocks. These catastrophes occurred before the creation of mechanical deposits and determined once and for all the major irregularities of the earth’s surface. Whatever consideration Dolomieu gave to geological agents of a regular nature, he did not envision them as capable of accomplishing large alterations in the mountains and basins created by these catastrophes. The source of the violent uplifting force causing this sudden rearrangement was uncertain, but might probably be chosen from among three possibilities—interior force, the loss of interior support (as in the creation of underground caverns), or exterior shock. Dolomieu inclined toward the last possibility. On consulting Laplace, Dolomieu was assured that normal gravitational forces could not account for such upheavals, but that either a passing comet or the “accidental” causes of volcanic eruptions might bring about catastrophic uplift.³

Following the process of upheaval, alterations in the rearranged depositions were brought about by “transport,” or mechanical deposits deriving from degradation of the mountainous uplands. These beds, however, were also disturbed from time to time by catastrophic currents, probably in the form of immense tides. Dolomieu steadfastly held to a belief in recurrent catastrophic alteration of the fundamentally established order of things, and in the greatly variable intensity of geological forces. His fascination with earthquakes was consistent with this catastrophism. Violent means were the principal causes of change in the earth’s surface, he thought, and his geological time scale was accordingly short. He thought 10,000 years to be a generous—even excessive—estimate of the extent of the era following the great catastrophic upheavals. Dolomieu therefore opposed the idea of the action of slow and cumulative forces bringing about geological change over a great period of time. Calling upon force rather than time as the cause of such changes, he wrote that “in fashioning the earth such as we inhabit it, nature has not spent time with as much prodigality as some celebrated writers have supposed.”⁴ Remarks of this nature and his denial that significant consolidation of rocks occurs in the ocean depths, at least along coasts, suggest that Dolomieu may have intended to make known his opposition to the main tenets of Huttonian theory, although no explicit references to Hutton are known among Dolomieu’s writings.

Dolomieu’s overall geological scheme, then, was not volcanist, but rather shared much in common with the opponents of doctrinaire volcanism. All the same, he was an authority on volcanoes and volcanic action, and spoke with an influential voice on the subject. One of his major concerns in studying volcanoes was the nature and source of volcanic ejecta. Dolomieu’s view of the mineralogical nature of lava depended on the conception of lavas as being warm and viscous, but never especially hot. An intrinsic source of heat within the lava, he believed, maintains the lava’s heat at a relatively even and moderate level. The exact identity of this intrinsic heat source was uncertain; it might be (or contain) sulfur, and it might be the same principle responsible for the binding action within certain rocks (such as granite), which always seem hard when unearthed but often crumble upon exposure to air, presumably because of the release of some substance that had joined the parts.

In any case, Dolomieu rejected any possibility of finding the source of volcanic heat in such fuels as coal or oil. On the other hand, there appears to be little ground for attributing to him a belief in an intense central heat within the globe. His investigations in Auvergne did convince him by 1797 that granites lie above the sources of volcanic eruptions and that the interior of the globe may therefore be fluid, but he did not cast aside the opinion that the modest heat of this viscous core comes from an intrinsic chemical source, such as caloric.⁵

The components of lavas are always traceable to a nonvolcanic origin, according to Dolomieu. In lava these components do not decompose, for the most part, but retain their mineralogical character. Volcanic heat does not destroy the older mineral composition, but merely “dilates” or “disunites” the integrant molecules, allowing them to slip past one another without being disaggregated. Lavas are therefore not vitrifications. The sources (foyers) of volcanoes are quite deep below the surface of the earth and are not limited to one particular type of rock, which explains the variability in composition of lavas. Many of Dolomieu’s writings reflect his serious concern to determine which mineral substances have been subject to volcanic action, as well as the effects of volcanic heat on the resulting rock. His deep knowledge of the precise nature of various volcanic ejecta was perhaps the main foundation of the respect accorded him by other scientists.

There is discernible in the development of Dolomieu’s thought a drift toward increasing interest in a theory of mineral classification and lithology, accompanied by a growing interest in what German mineralogists were doing. In the early 1780’s Dolomieu secured a shipment of Saxon mineral samples through the assistance of Johann Friedrich Charpentier, professor at the Freiberg Bergakademie, and shortly before his death Dolomieu was planning a trip to Freiberg to visit Werner and perhaps take steps toward a reconciliation of German and French mineralogies.

Dolomieu clearly felt a certain affinity with Werner, but his greatest expressions of mineralogical debt and admiration were reserved for Haüy, whom he regarded as the founder of a new and highly fruitful approach to knowledge of mineral substances. Dolomieu came to believe in the importance of the form and constitution of the constituent structural unit, as opposed to the relative quantity of constituent substances, in determining a mineral substance’s characteristics. His commitment to the integrant molecule as the basis of a new mineralogy is recorded in Sur la philosophie minéralogique, et sur l”espèce minéralogique (1801), which he had begun to compose during his imprisonment and in which he pursued the hope of raising mineralogy to the degree of precision that had recently been achieved, he thought, by chemistry.

Dolomieu was excited by the prospect of reducing the variety of mineral appearances to the chemical and spatial properties of the unique integrant molecule—which by definition established mineral species. Part of his excitement derived from his recognition that by assuming the integrant molecule to exist, one avoided having to deal with mineral species as only a matter of convention.

In light of Dolomieu’s avowed empiricism, it is interesting that he saw this promising new development in mineralogy as the outgrowth of conceptual, not observational, investigation; species cannot be definitively distinguished by any mechanical operation, but only in the mind. On the whole, however, Dolomieu regarded himself as a scientist firmly rooted in observational technique. His many trips in the volcanic regions of Italy, in the Alps, and in other areas of geological interest were part of his program for geological investigation, and his mineral collection appears to have been a major focus of his empirical energies, especially early in his career.

Dolomieu was, however, given to making occasional tributes to experience as the fount of scientific knowledge. The scientists he praised most highly were often observationalists like Horace Bénédict de Saussure. He was inclined to see disputes over geological issues as resolvable by recourse to simple observation, if not by reasonable determination to eliminate unnecessary semantic disagreement. In the turmoil of doctrinaire controversy in geology at the end of the eighteenth century, he saw himself as a practical-minded and moderate scientist with excellent credentials as a mediator between rival extremes.

Dolomite was named after Dolomieu by Nicolas Théodore de Saussure, to whom Dolomieu had given samples of the substance after describing it as a calcareous rock from Tirol that was attacked by acid without effervescence.⁶