286 EXPERIMENTS ON METAMORPHISM AND 



The fossil vegetables having undergone modifications under the in- 

 fluence of the same agents as stony matters, it is proper to see what 

 becomes of wood in superheated water. Fragments of spruce were 

 transformed into a black mass, having a bright lustre, perfectly com- 

 pact — in a word, presenting the aspect of a pure anthracite ; it was so 

 hard that a steel point could with difficulty scratch it. This kind 

 of anthracite, although infusible, is entirely granulated under the 

 form of regular globules of difterent dimensions, from which it clearly 

 results that the substance has been melted in the process of trans- 

 formation ; b}^ calcination it yields only traces of volatile matter ; the 

 ligneous matter has therefore arrived at its last stage of decomposi- 

 tion. This kind of compact carbon burns very slowly, even under 

 the oxidizing flame of the blow-pipe. It difl"ers from the carbons 

 formed at high temperiitures in the fact that, like the diamond, it does 

 not conduct electricity. The veins of silver at Kongsberg, in Nor- 

 way, which are encased in gneiss, contain anthracite which very 

 much resembles the artificial anthracite we have just mentioned. It 

 has moulded itself in the midst of carbonate of lime and native silver, 

 under a form thai shows that it has passed through a softened state. 

 At lower temperatures, but in conditions otherwise analogous, wood is 

 transformed into a kind of lignite or coal. In these experiments I 

 obtained, as I have before said, liquid and volatile products resem- 

 bling natural bitumens, and possessing even their characteristic odor. 



To recapitulate : superheated water has a very energetic influence 

 on the silicates ; it dissolves a great many of them, destroys some 

 combinations of multiple bases, and forms new ones, either hydrated 

 or anhydrous ; in fine, it causes those new silicates to crystallize far 

 below their point of fusion. In these changes the silicic acid, set at 

 liberty, isolates itself under the form of crystallized quartz. Trans- 

 formations so complete are, moreover, obtained with a ver}^ small 

 quantity of water. In general we can distinguish this law, that near 

 the point of nascent red heat the affinities of the wet way acquire, so 

 far as concerns the production of silicates, the same character with 

 those of the dry way. . 



CHAPTER V. 



DEDUCTIONS DRAWN FROM THE PRECEDING EXPERIMENTS, FOR THE EX- 

 PLANATION OF THE CRYSTALLIZATION OF SILICIOUS, ERUPTIVE, AND META- 

 MORPHIC ROCKS. 



The results which we have just given enable us to account for what 

 takes place in the crystallization of silicious rocks in general, as well 

 the eruptive as the metamorphic. Let us first examine the former of 

 these, commencing with the lavas. 



Whatever may be the molecular state of the water in lavas, it in- 

 tervenes to cause them to crystallize much in the same way as in the 

 experiments of the laboratory for transforming obsidian into crystallized 

 feldspar, and for producing pyroxene in perfect crystals. Thus, in 



