The work of mapping the processes of geological formation is entangled with the process of extraction from deep time – a conquest figured in relation to the coal measures. Building on Alfred Gell’s approach to the relationship between time and the ways in which it is culturally constructed, this chapter addresses the question ‘Whose time is deep time?’ through a consideration of the politics of marking the boundaries of time in nineteenth-century Imperial Britain, with a particular focus on the Cambridge geologist Adam Sedgwick.