This article reveals new connections between Sand and Flaubert by examining their shared interest in geology. Focusing on Flaubert’s L’Éducation sentimentale (1869) and Bouvard et Pécuchet (1880), and Sand’s understudied later works, particularly Jean de La Roche (1860), the article considers these writers’ engagement with Georges Cuvier’s catastrophist model of earth history as developed in his Discours sur les révolutions de la surface du globe (1825). It argues that Sand and Flaubert’s works illustrate rich intersections with geohistory, specifically with regards to temporality and humanity’s changing relationship with the environment. Whereas Flaubert draws on Cuvierian geology to develop a fractured conception of history, Sand takes the upheavals of the earth’s past as a model for humanity’s struggle towards moral and spiritual progress. Both authors, however, also draw on the deductions of geology to question humanity’s pre-eminence. Their shared attraction to earth history as a means of challenging the supremacy of humankind destabilizes conventional readings of Sand and Flaubert as polar opposites. Through their engagement with geology as a mysterious conceptual space, the two authors reach towards a deeper union with the wider universe beyond the limitations and oppositions of the present.