Earth, air, fire and water: the consolidation of clastic strata in Hutton’s Theory of the Earth

Hutton made great contributions to geology, including his version of the rock cycle. A vital component of this cycle was the ‘consolidation’ of loose sediment into sedimentary rock. Hutton argued that consolidation was driven by heat, in the sense of the softening or melting of minerals. A counter hypothesis, that consolidation was enabled by aqueous reactions, was considered and rejected, using examples from sandstones, sinters, coal, ore minerals, salt and septarian concretions. A central plank in Hutton's arguments was the insolubility of minerals in water, though Hutton actually cited plenty of examples that clearly demonstrate solubility, and has contradictory statements on this vital fact. One of Hutton's main adversaries, Richard Kirwan, critiqued Hutton's work and used contemporary chemical knowledge to argue strongly for consolidation by aqueous reactions. Hutton also relied upon the idea that some rocks such as flint ‘appear’ to have been molten, an argument the modern reader may find difficult to accept. Hutton has ultimately been judged to have erred on the topic of consolidation. The modern study of sedimentary diagenesis is entirely focused on aqueous reactions, with the role of heat relegated to the control of the rate of aqueous reactions, with increasing rates as temperatures increase.