Early texts on the Cenozoic fossils of Aquitaine (1622–1767) and pioneering debates on the organic origin of fossils, the superpositioning of strata and the mobility of the seas

Abstract

Several unpublished or little known writings from the 17th–18thcenturies deal with the Bordeaux region’s “figured stones”, which are actually Miocene fossils. The oldest work is a book by Pierre de L’Ancre (1622), where the author describes the shelly sediments of Sainte-Croix-du-Mont and relates Louis XIII’s visit there in October 1620. De L’Ancre is unsure as to the origin of the fossil shells, which could be ascribed to consolidation of the host sediments during lengthy ages after a withdrawal of the sea, transport from the Ocean by the Flood orin-situdevelopment through « esbatement de la nature » (i.e., a freak of nature). His text is remarkable for its description of the layers, which the author names « estages » (i.e., stages) and describes from the bottom up, suggesting that he grasped the principle of superposition later developed by Steno (1669). A later manuscript, kept at the Arsenal Library in Paris, was written between 1631 and 1673 by an unknown author: entitledReflections sommaires sur quelques pierres de la Terre de Sales. It deals with the origin of the fossils in the shelly sands of Salles, south of Bordeaux. The author prefers the hypothesis ofin-situdevelopment in soil rather than an organic marine origin, thus remaining faithful to the “freaks of nature” thesis frequently accepted at the time. In the 18thcentury, the Bordeaux Academy discussed the origin of these fossils. In 1718, Father Jules Bellet and Isaac Sarrau de Boynet studied the shells of Sainte-Croix-du-Mont; they suggested an organic origin in view of the scar left by the adductor muscle on the shells and the effervescence of the latter in vinegar. Sarrau de Boynet, however, refused to admit that the sea had reached this village and adopted the extravagant thesis of an anthropic accumulation of oysters, which Montesquieu approved only reluctantly. From 1745 on, Jacques-François Borda d’Oro began the study of Eocene sites and fossils in the Dax region; the observation ofLithophaga, incompatible with a transport by the Flood, reinforced him in his conviction of a marine origin. Nicolas Desmarest observed fossils in 1761, in particular near Saint-Émilion, and was convinced of their marine origin. In 1743 and 1745, the Bordeaux Academy organized essay competitions on the origin of the “figured stones”. The candidates were in favour of the organic origin, but ignored the shelly sediments of the region. One of these candidates, Pierre Barrère, surprisingly states the principle of uniformitarianism as early as 1745. These writings, among the first devoted to the geology of the Aquitaine Basin, illustrate that certain basic elements of modern palaeontology and stratigraphy were already grasped in the 17thand 18thcenturies.