This paper relates developments in the science of geology to forms of governmental rationality in Canada during the late nineteenth century. By so doing it opens for discussion a topic rarely broached by political theorists: the role that the earth sciences played in the historical evolution of forms of political rationality. The paper contests theoretical approaches that understand the relation between scientific knowledge and state rationality as only instrumental. Instead, the paper demonstrates how attending to the temporality of science (as evident in the emergence of specifically geological ways of seeing nature during the period) helps us understand the ways in which science is constitutive of political rationality, rather than merely its instrument. This argument is developed through a critique of Michel Foucault's concept of 'governmentality', a concept that historicizes political rationality, yet remains silent on how the physical sciences contributed to its varied forms. The paper concludes with reflections on the implications of such an argument for theories of the social production of nature.