Late seventeenth century ideas about volcanic activity were largely derived from classical sources. The Philosophical Transactions of the Royal Society of London provided a vehicle for publication of information about volcanoes where many ancient notions were refuted and new hypotheses suggested. Volcanic studies by members included detailed field reports, eyewitness accounts of eruptions as well as expeditions to extinct or dormant volcanic peaks, experiments with volcanic rocks, and speculation on the nature of subterranean "fires" and causes of eruptions. The development of theories concerning the formation of the columnar basalts of the Giant's Causeway is also traced. By the 1770's there appeared a general acceptance among members of the Royal Society of the igneous origin of basalt, the existence of ancient extinct volcanoes and the implications of past geologic change.