90 Sketch of the Mineralogy 



bourg, in Germany. Thence the two systems are call- 

 ed the Iluttoman and the Wernerian., or, because the 

 former employs fire, and the latter water, as the great 

 agent, they are frequently denominated the Plutonic and 

 the Neptunian systems. According to Dr. Hutton, the 

 whin stone is a product of subterranean heat. He sup- 

 poses it to have been once in a semifluid state, and in 

 that condition to have been forced from below upward 

 among the superior strata by subterranean fire, where, 

 by slow cooling, he imagines it assumed the stony cha- 

 racter, and crystaline texture ; for, it must not be for- 

 gotten, that when whin stone is melted by our com- 

 mon furnaces, and suffered to cool rapidly, it becomes 

 mere glass, and, as the lavas are not viterous, but pos- 

 sess the stony and crystaline character, this was suppo- 

 sed by the opponents of the Huttonian theory, to prove 

 that lava and whin stone could not have had the same 

 igreous origin, since, if that \^^^v^ the case, the melted 

 whin ought, on cooling, to assume the appearance of 

 stone, and the crystalized form usually observed in the 

 lavas, instead of the vitreous character which alone, af- 

 ter fusion, it had hitherto exhibited. But this objection 

 has been removed by the experiments of Sir James Hall, 

 of Edinburgh, who has found that when melted whin 

 stone is cooled very slowly, and with a regulated tempe- 

 rature, it resumes completely the stony and crystaline 

 character ; moreover, that lava itself, if cooled rapidly, 

 becomes a mere vitreous slag ; if slowly, it exhibits 

 again the proper appearance of lava, and that the same 

 specimen of whin stone or of lava may, in this manner, 

 be converted at pleasure into glass or stone, and this 

 as often as the experimenter chooses ; nay, that even 

 common bottle glass may, by slow cooling, be convert- 

 ed into a perfect stone, and then by melting anew and 

 rapid cooling, it may be restored to the state of glass 

 again. It has happened to the writer to see most of the 

 original specimens upon which these conclusions were 

 founded. 



In the opinion of the Huttonian geologists, they justi- 

 fy the conclusion that lava and whin are both of igneous 

 origin ; the former actually erupted into day light, and 



