In his *Protogea* (1692), Leibniz explained fossils and sedimentary layers as resulting from the biblical flood. The same explanation occurs in the work of the three first English geologists Burnet (1682), Woodward (1695) and Whiston (1696): all of them were “catastrophists.” For this school, ages of the Earth do not matter because rapid changes interrupt periods of stability: for them, time is not a cause by itself and changes in the landscape result from mechanical causes, either volcanism or “plutonism.” Such a biblical worldview was soon to be attacked by many “systems of the Earth” that appeared from the mid 18th century.
After Buffon (1749), Hutton was the founder of “uniformitarianism” or “actualism”: long ages became the necessary hypothesis for everyday phenomena (as erosion or river deposits) to cause large scale effects. For Hutton, Playfair or the French encyclopaedists (Voltaire, Diderot or d’Alembert, the latter being the Secretary of the Academy of Sciences), the Mosaïc Flood was not to be taken literally and Geology could and must rely exclusively on natural and actual explanations. Exceptionally, Jean-André Deluc (1727-1817), a Calvinist who taught geology at Göttingen, kept the former distinction between present phenomena still operating and observed, and past causes known only from their effects, these being realities that present causes cannot explain.[1](http://www.kolbecenter.org/tassot_symp02.htm#sdfootnote1sym)
Deluc considered two creative periods: the six Days of Creation and the Flood. Only these periods could explain the formation of rocks. Deluc understood perfectly the issue at stake. In His *Elements of Geology* published in London in 1809, he noted how the enemies of Religion had switched their attack to geology. Theologians should, therefore, study geology a they do ancient languages. Geology, said Deluc, is presented as a true science based on evidences and rigorous deductions. If people consider that geology is contrary to Genesis, they will necessarily conclude that Genesis is only a legend.
Deluc was a first rank scientist of the time. He taught geology to Cuvier, the French natural scientist who believed in the Great Flood. Emigrating to England in 1773, Duluc was immediately accepted as a member of the Royal Society and became lecturer to Queen Charlotte. One day, visiting Voltaire in Switzerland at his mansion in Ferney, he asked the philosopher his opinion about Moses. “*Moses, *said Voltaire*, was a deceiver leading a stupid people.*” “-*But*, answered Deluc, *Moses is the historian of the Earth and of Man. If he told the truth on these points at a time when Geology was not even born, it is necessary to conclude that he wrote by Revelation.*”[2](http://www.kolbecenter.org/tassot_symp02.htm#sdfootnote2sym) Confronted by Deluc, Voltaire was unable to argue for the long ages of the Earth and against the Flood.
Father Emery, the head of the Sulpicians (the Congregation which taught in the French seminaries), heard that Deluc had silenced Voltaire and understood immediately the importance of geology in apologetics. He asked Deluc for permission to translate his “*Letters to Blumenbach*” into French: for such an apologetic, the difference of creeds between Catholics and a Calvinist could be set aside. Moreover, after the political Revolution in Europe, minds were open to past geological “revolutions.” Somehow the Revolution proved that history admitted discontinuities. In 1812, Cuvier published his famous *Discourse on the Revolutions of the Earth.* Transformists, he wrote, were wrong because:
If the species did change by degree, we should find the traces of these gradual modifications, (…) we should discover some intermediary forms and, till now, this has not happened.[3](http://www.kolbecenter.org/tassot_symp02.htm#sdfootnote3sym)