James Hutton (left) and Joseph Black (right), natural philosophers, talking together. Etching and aquatint by J. Kay, 1787.

Hutton, based in Edinburgh, was a farmer and author of works on geology, agriculture, and scientific method. Joseph Black was Professor of Medicine and Chemistry at Edinburgh University 1766-1793. "[James] Hutton spent more time with [Joseph] Black than anyone else, often in scientific pursuits. … For relaxation in his later years he used 'regularly to unbend himself with a few friends' … at the Oyster Club, an informal group he formed with Black and [Adam] Smith where they got together with savants, manufacturers, and entrepreneurs."-- Oxford dictionary of national biography