SAUSSURE, HORACE BéNéDICT DE

(b. near Geneva [Conches], Switzerland, 17 February 1740; d. Geneva, 22 January 1799), geology, meteorology, botany, education. For the original article on Saussure see DSB, vol. 12.

When Saussure died in 1799, his personal archives were given by the family to the public and university library of Geneva where they were left untouched until 1975 when the author of this postscript decided to study the numerous manuscripts brought to light and discovered astonishing conditions. The only printed version of his work was available under the title Voyages dans les Alpes…(1779–1796). The general reader was in a rather strange situation for more than two centuries. It was as if Saussure, the founder of Alpine Geology, had gathered an enormous amount of observations throughout his entire life from which nothing new pertaining to the fundamental mechanisms that built the Alps was extracted.

The Voyages dans les Alpes … The major obstacle originates from the fact that Saussure could not describe all his travels without needless repetitions. Therefore he made the choice of preparing a pastiche consisting of the best descriptions organized into seven ideal voyages dealing with the major massifs, valleys, and structures regardless of the dates of their best original description. Interspersed in the narrative are very short sections dealing with theoretical interpretations, but they are too short and cryptic to give real clues on the evolution of the author’s thinking. Consequently, it is not possible to unravel the path of his geological thinking. Not enough appears to have been provided besides the repetition of the statement that more observations were needed and that the major theoretical discussions would be postponed. The main focus was a final theory of the Earth. Unfortunately his poor health prevented him from writing, and he died in 1799. Only two abbreviated tables of contents were published in 1786 and in 1796 respectively.

More than two centuries passed during which Saussure fell into oblivion or was designated with the unwarranted label of a simple observer while hundreds of his field-note booklets and other manuscripts were carefully preserved but remained unstudied. These texts contain in perfect chronological order the detailed account of the discovery of a major principle of structural geology as demonstrated by Saussure in the Alps and accepted in the early twenty-first century as fundamental in mountain building in general—horizontal overthrusting. From time to time the non-scientific portions of the Voyages dans les Alpes… were republished by anonymous editors to satisfy the curiosity of the general public under the title of Partie Pittoresque des Voyages de M. de Saussure.

Saussure undertook important field trips outside the Alps and their related manuscripts concerning the basalt in Italy (1772–1773), in Auvergne and Vivarais (1776), and other places in Europe also contain critical data. The same is true for his lecture notes on physical geography at the Academy of Geneva (1775) and many aspects of physics and metaphysics that remain to be evaluated.

The Manuscripts in Chronological Order Saussure’s manuscripts were written mostly in the field in pencil and finalized within at least twenty-four hours in pen every day. This remarkable suite of observations represents a perfect time sequence from which the evolution of his geological interpretations can be obtained. Saussure’s notes are in French and occasionally in Latin. The original language was followed by an English translation and footnotes explaining the geological problems in ancient and modern terms and by following his itineraries step by step. Overlapping dates of the manuscripts results from the fact that Saussure investigated various subjects simultaneously during a given period of time.

Early Alpine Structure Concepts These observations (Ms 1760–1775) pertain to the structural features of the Salève mountain overlooking Geneva, those of the Jura Mountains at the Dôle, and between Pontarlier and Besançon. The problem common to these folds was to understand the cores of the structures made of vertical limestone beds pushed upwards through younger strata leaning against them at variable angles (so-called folds in A). Other parts of the High Calcareous Alps display spectacular S-shaped folds (such as at the Arpenaz Cascade) forming recumbent structures with adjacent cavities in the landscape left open when the limestone beds were folded upon themselves.

Saussure was confused by all this structural complexity. For the time being he proposed a variety of interpretations that cover the whole spectrum of unsupported theories of his time. These included a kind of crystallization on the seafloor generating structures comparable to the microscopic folds of agate concretions or subterranean forces of unknown origin, or even subterranean fires although no traces of their action was visible.

The Cramont and Vallorcine Saussure proposed a new mechanism (Ms 1774–1778) derived from the panorama as seen from the summit of the Cramont (a peak located immediately south of Mont-Blanc). According to him, the primitive and secondary rock layers were deposited horizontally on the seafloor. The explosion of elastic fluids in subterranean caverns uplifted the primitive rocks in a vertical and contorted position while cutting across the overlying secondary rocks. These secondary rocks remained leaning against the primitive ones at an angle that decreased gradually away from the center of the Alps. The originality of this approach was in the vertical force due to the explosion of the elastic fluids that left no traces. An earlier theory using the action of fire was eliminated from the working hypotheses by Saussure’s new theory.

Saussure then tried to characterize his concept of vertical force by investigating the various types of conglomerates, in particular those of Vallorcine (near Chamonix),

Horace Bénédict de Saussure . Horace Bénédict de Saussure, circa 1760. ROGER VIOLLET COLLECTION/GETTY IMAGES .

that were in the critical intermediate position between the vertical primitive rocks and the tilted, overlying secondary ones. These conglomerates displayed huge and spectacular angular to rounded boulders of granite in a purple, shaly matrix. This unusual rock type was interpreted by Saussure as indicating a powerful process of fragmentation followed by redeposition according to the size of the clasts in a quiet aqueous environment. These depositional events were followed in time by the general uplifting of the beds. The final conclusion reached was that these conglomerates represent the product of violent earthquakes and consequently that mountain building is a seismic process. This interpretation is a theoretical challenge still under consideration by modern geologists. Unquestionably, Saussure was well informed about the spectacular effects of the numerous earthquakes of his century from reading books and periodicals.

Saussure’s Scientific Library From the early part of his career, Saussure had been deeply concerned about being up-to-date with the progress of the various sciences of interest to him, in particular geology and mineralogy, but also botany, chemistry, astronomy, physics, mathematics, and philosophy. By wisely using his personal wealth he began to assemble a systematic library. Two catalogs in his own hand (Ms 1788–1797) show holdings of at least 1,202 items, that is 1,143 books and 59 periodicals published by learned societies from all over Europe. Rapidly, it became one of the most diversified collections of the eighteenth century. Related correspondence with major book dealers of Europe reveals an extensive network of purchases and sales. He bought between 1760 and 1768, 1,034 volumes, that is, sixty-five percent of the final library he needed for his research. The major reason for such a collection lies in the fact that Geneva was a relatively isolated city-state and that purchasing books was the only way to keep abreast with scientific development in all fields. However the French Revolution and its turmoil led to the loss of Saussure’s fortune, and many precious holdings were sold at auction to his profound chagrin.

Basaltic Volcanism Saussure wrote a series of manuscripts on the origin of prismatic basalt in Italy, Auvergne, Vivarais, Provence, and Brisgau (Ms 1772–1798). In particular, he wanted to see for himself the examples described in the Massif Central of Auvergne by Nicolas Desmarest who had demonstrated the volcanic origin of basalt by following large prismatic lava flows from the plains up the slopes of scoriaceous cones into the corresponding craters.

Saussure returned from his trip to Auvergne an enthusiastic believer in the volcanic origin of basalt. However, through the years of investigating rather superficially many outcrops, and by accepting the neptunian ideas of Abraham Gottlob Werner, he tempered his position to the extent of assuming two types of basalt: an aqueous deposit and a volcanic lava. Eventually, he believed only in a water-laid origin. In defense of these strange changes of concepts it should be pointed out that Saussure happened to come across many unusual types of basalt that he did not study in sufficient detail. Furthermore he was a famous geologist who had to take a position in the controversy. He took the erroneous one as demonstrated by James Hutton who introduced the modern ideas on the subject at the time of Saussure’s death.

Lectures on Physical Geography The documents pertaining to physical geography (Ms 1775) are of three major types. A first version written in French on index cards that is the most personal document and a second version in Latin also on note cards—now lost—which is the required language of the oral academic presentation. The third version is a complete Latin text, not from Saussure’s hand but a manuscript carefully copied in 1786 by one of his students, Jacques-Louis Peschier. Among the references in this unique manuscript two famous works are constantly quoted, criticized, or praised without restrictions, namely George-Louis Buffon’s Théorie de la Terre (1749) and The Physikalishe Beschreibung of Olof Torbern Bergman (1766). Of great interest is the spontaneous presentation of the index cards in French which has a completely informal style with so-called red flags reminding the speaker to attract the attention of the students to important aspects of the presentation. A similar technique is still used by experienced lecturers.

Horizontal Thrusting in Opposite Directions These manuscripts (Ms 1780–1784) pertain to a large structure of tertiary sandstones (Molasse) of Albi-sur-Chéran: Saussure briefly looked at this structure in 1780. He observed that at this location it could only be formed by horizontal thrusting in opposite directions—a new concept given without any further comments. Returning to the field in 1784 and after detailed studies he presented a speculation of great importance. According to Saussure horizontal thrusting in opposite directions implied not only a detachment (décollement) of the Earth’s crust from its substratum, but also a general shortening of the seismic system and finally present-day antagonistic stresses that maintain the Alpine structures at their high elevation. The date of this critical observation was 13 October 1784. He even went so far as to suggest laboratory simulations with clay layers, becoming a pioneer of experimental geology.

It is difficult to understand such a concise discussion of a fundamental concept without much consideration, and Saussure’s style does not help. It can be better explained by a modern interpretation using a transverse cross-section trending through the Valley of Chamonix and the summit of Mont-Blanc. If overthrusting tilted the rocks from an original horizontal position to their present vertical one and the bottom of the Valley of Chamonix represents the ancient surface of the crust then the horizontal distance between the Chamonix Valley and the top of Mont-Blanc corresponds approximately to the thickness of the crust that has been overthrusted. Therefore, the summit of Mont-Blanc, which reaches in the twenty-first century the elevation of about one league over the present surface of the globe, was originally buried at a depth of more than two leagues (8.8 kilometers) below that surface.

The Alps and World Mountains In summary, Saussure (Notes of 6 July 1795) considered a worldwide application of his structural ideas to the origin of the great orogenic belts. He stated that it is not at the great depth of coal mines but on the top of mountains consisting of vertical beds uplifted in such a position and maintained in it by the permanent stresses of earthquakes, that lie the answers of modern tangential tectonics.

SUPPLEMENTARY BIBLIOGRAPHY

Carozzi, Albert V. “Découverte d’une grande découverte:Horace-Bénédict de Saussure et les refoulements en sens contraires dans la formation des Alpes.” In Les Plis du Temps, mythe, science et H.-B. de Saussure, edited by Albert V. Carozzi, Bernard Crettaz, and David Ripoll. Geneva: Collection Nouveaux Itinéraires Amoudruz, No. 5, Musée d’Ethnographie de Genève, Annexe de Conches, 1998.

——. Manuscripts and publications of Horace-Bénédict de Saussure on the origin of basalt (1772–1797). Bilingual Volume. Geneva: Editions Zoé, 2000.

——. Horace-Bénédict de Saussure (1740–1799): Un pionnier des sciences de la Terre. Geneva: Editions Slatkine, 2005. This is the most recent biography.

———, and Gerda Bouvier. The Scientific Library of Horace Bénédict de Saussure (1797): Annotated Catalog of an 18th-Century Bibliographic and Historic Treasure. Mémoires Société de Physique et d’Histoire Naturelle de Genève, vol. 6, 1994.

——, and John C. Newman. Lectures on Physical Geography Given in 1775 by Horace-Bénédict de Saussure at the Academy of Geneva. Trilingual volume. Geneva: Editions Zoé, 2003.

Albert V. Carozzi