One of the founders of modern geology. When the middle-aged Hutton returned to the intellectual ferment of Edinburgh, Smith, Black and Watt became his most important friends. Most, along with Hume and Ferguson, were members of the convivial and influential ‘Poker Club’, with its sherry, claret and shilling dinners. Hutton and Playfair made a voyage to examine coastal rock formations, though Playfair (who helped spread his ideas) regretted that Hutton’s dense prose got in the way of his work’s appreciation. On a geological tour of England, Hutton dragged Watt around salt-mines and conducted elaborate experiments with Edgeworth and Darwin.