The interplay between observation, theory and experiment focused on the birth of geology as a science, during the period of the Scottish Enlightenment. The fires of Hutton's (1726-1797) Plutonists couls not be quenched by the oceans of Werner's (1750-1817) Neptunists. Hall (1761–1832) was convinced that Hutton’s “Theory of the Earth” could be proved by experiments, but he deferred to the fears of his older colleague that failed experiments might discredit the Theory (which needed no further proof), and completed the experiments only after Hutton’s death. Hutton censured those who “judge of the great operations of the mineral kingdom, from having kindled a fire, and looked into the bottom of a little crucible.” Hall believed that “the imitation of the natural process is an object which may be pursued with rational expectation of success.” Following many discussions between Hutton and Hall, three topics were pursued in Hall’s experiments: 1790, the magmatic origin of granites, younger than schists; 1798, whinstones/ dolerites are as magmatic as known lavas; 1805, powdered calcite is transformed to marble and melted by the effects of compression (and water) in modifying the action of heat. The latter involved the first high-pressure, high-temperature apparatus and earned Hall the title “Father of Experimental Petrology”. Subsequent development of these three topics is outlined, with particular reference to Scottish contributions, and to debates about primary basalts, granitization, and carbonatites.