I just stumbled upon An Introduction To Geology by British geologist Robert Bakewell (1768-1843). Originally published in 1813, it is the first textbook on geology in the English language, and was described by Davis Young (author of Mind Over Magma: the Story of Igneous Petrology) as "The first modern textbook on geology". On page 276, titled Volcanic Products, I discovered the following passage:
The substances ejected through fissures in the earth, or volcanoes, belong to the four grand divisions of the mineral kingdom,--the inflammable, saline, metallic, and earthy.Abiotic petroleum origin 1; fossil fuel cult 0.
The inflammable substances are sulphur, carbon, and hydrogen. The inflammable quality of sulphur prevents its being found in lava in a solid form; during volcanic eruptions it is evolved in a gaseous state combined with hydrogen. It is also sublimed from the fissures of extinct or dormant volcanoes, and forms thick incrustations on the sides of craters. Almost all the sulphur of commerce in Europe is procured from the craters of dormant volcanoes in the south of Italy, Sicily, and the Lipari Islands. When the combustion of sulphur in volcanoes takes place where there is access to atmospheric air, it forms sulphurous acid gas, and sulphuric acid.
Carbon combined with hydrogen, forming bitumen, is found in volcanic rocks, and also in some basaltic or trap rocks. The volcanic tufa in the vicinity of Clermont, in France, contains so much bitumen, that in warm days it oozes out, and forms streams of bitumen resembling pitch, which is more remarkable, as this tufa must have been erupted some thousand years. Bitumen has been observed oozing out of the lava of Etna. The moya ejected from the volcanoes in the Andes, in aqueous or muddy eruptions, contains so much bitumen or carbon, as to be inflammable. As bitumen exists in many volcanic rocks, the black smoke which issues during an eruption may proceed from its combustion, though it has been generally supposed to consist of minute volcanic sand, called ashes. Carbon also combines with hydrogen in a gaseous state, and forms carburreted hydrogen gas.
The hydrogen gas evolved from volcanoes, or from chasms in the earth during earthquakes, is generally combined with sulphur or carbon; it is probably formed by the decompostion of water, when it finds access to subterranean fire.