GROWTH OF EXPERIMENTAL SCIENCE 173 



An experiment is described by several writers of this period which was 

 considered by them to demonstrate that it was to the presence of great 

 deposits of self -igniting sulphurous minerals in the earth's crust we must 

 look for the cause of volcanic action. The experiment consists in mixing 

 several pounds of iron filings in equal parts with sulphur, moistening the 

 mass with water, and burying it to a depth of a few feet in the ground. 

 Presently, we are informed, it begins to heat, and in a few hours the 

 earth will begin to tremble and crack ; fire and smoke will burst through, 

 and it is only necessary to postulate a sufficient quantity of this mixture 

 to produce a true Etna. "This experiment, continues one author, suffi- 

 ciently explains and illustrates the cause of earthquakes, volcanoes, and 

 all fiery eruptions from the earth, for nothing more is requisite than 

 iron, vitriolic acid, and water; and iron," he continues, "is generally 

 found accompanied by sulphur." 



Such early experiments, while they have no real importance or value, 

 may be taken as an evidence of a growing interest in the experimental 

 method and as the forerunners of more important and serious work which 

 was to follow in later years. 



It was the well known controversy between the Neptunists and the 

 Plutonists that afforded the first striking example of the importance of 

 experiment in geology. 



The Neptunists held that fire, while liquefying substances by fusion, 

 could never produce crystalline bodies, since the -fused mass in cooling 

 was always glassy in character. A crystalline structure could, according 

 to their tenets, be produced only by deposition from solution. They held, 

 therefore, that crystalline rocks — as, for example, basalt — could not have 

 been produced by fire, but must have originated by deposition from water. 



They held, furthermore, that not only were basalts and similar rocks 

 of sedimentary origin, but that the crystalline schists, gneisses, etcetera, 

 had originated in like manner, and adduced as further proof of this fact 

 the fact that bodies of crystalline marble were in places found inclosed 

 in these schists, which showed that the inclosing rocks had never been 

 subjected to heat, since, had this been the case, the carbonic dioxide would 

 have been expelled from the marble and quicklime only would have 

 remained. 



Hutton, on the other hand, following the teaching of the Plutonists, 

 held that the crystalline schists and other crystalline rocks had solidified 

 from a molten condition, and that the magmas from which they had 

 developed would, if cooled very slowly, yield distinctly crystalline, or even 

 coarsely crystalline, rocks, and that even "stones^ of the calcareous ^enus 



Playfair's Illustrations of the Ilnttonian Theory, vol. i, p. 45. Edinburgh, 1822. 



