The introduction outlines a history of oscillation between the strange pleasures offered by geological knowledge and the cultural and colonial structures propped up by the geological timescale. In the first half of the nineteenth century, geology was the site of novel ideas, endowing ordinary surroundings and common substances with awe-inspiring temporal heft and complexity and offering a space to speculate about otherness. At the same time, it worked to sediment colonial power and reserve the “humanity” that geology brought into view for a select subset of the species. Geological fantasy, the cultural form that made these effects possible, is explained with reference to some of the forms it took both in the nineteenth century, when geology was first in vogue, and in our own moment, when it has become so again.