Students have no trouble grasping this extended inference, and they do appreciate the point. Harder to convey is the revolutionary concept embedded in this inferred history, for Hutton's work helped to incorporate it among the commonplaces of modern thought. The revolution lies in a comparison with previous geological theories that included no mechanism for uplift and viewed the history of our planet as a short tale of uninterrupted erosion, as the mountains of an original topography foundered into the sea. This debate did not pit biblical idolatry against scientific thinking, as so often misportrayed; for as I noted in the last chapter, Steno's mechanical view shared with other seventeenth-century geologies the theme of continuous erosion as the organizing principle of history.

The pivot of debate was, instead and again, time's arrow and time's cycle. Hutton, I will argue, did not draw his fundamental inferences from more astute observations in the field, but by imposing upon the earth, a priori, the most pure and rigid concept of time's cycle ever presented in geology—so rigid, in fact, that it required Playfair's recasting to gain acceptability. Playfair aided Hutton's victory by soft-pedaling the uncompromising and ultimately antihistorical view of his late and dear friend.

In any case, this picture, and the unconformity that it represents, gains its cardinal significance as the primary item of direct evidence for time's cycle and an ancient earth. One can present abundant theory (as Hutton did) for the role of heat in uplifting strata, but unconformities are palpable proof that the earth does not decline but once into ruin; instead, by following decay with uplift, time cycles the products of erosion in a series that shows, in Hutton's most famous words, "no vestige of a beginning,—no prospect of an end" (1788, 304).

Hutton's World Machine and the
Provision of Deep Time