§36. REVIEW OF THE HYPOGENE ROCKS. 873 



long-continued and intense heat, produced under circum- 

 stances which have given to the resulting rocks a very 

 peculiar character. 



The transmutation of chalk into crystalline marble — of 

 loose sand into compact sandstone — of argillaceous slate 

 into porcelain jasper — of coal into anthracite — of anthracite 

 into shale and slate — of slate into micaceous schist — of mi- 

 caceous schist into gneiss and granite — of the latter into 

 trap — and so forth — together with the characters presented 

 by the mineral products of existing volcanoes, prepare the 

 mind to receive without surprise the assertion of an eminent 

 geologist and chemist, M. Fournet ; that all the "primary 

 rocks are probably sedimentary deposits metamorphosed by 

 igneous action; * this opinion, however, is but a modification 

 of that long since expressed by our illustrious countryman, 

 Hutton. 



There is one striking deduction which M. Fournet has 

 drawn from the mineralogical character of these rocks, 

 namely, that those masses which, according to our chemical 

 knowledge, would require the most intense and long-con- 

 tinued incandescence for their formation — i. e. those in 

 which quartz largely predominates — are precisely those 

 which from their geological position must have been longest 

 exposed to such an agency ; hence, in granite the founda- 

 tion rock, quartz, which is the most infusible and refractory 

 material, largely prevails. The possibility of an earth being 

 converted by intense heat ino the hardest and purest crystal, 

 was shown in the formation of fictitious rubies (p. 866). To 

 the granite succeed rocks in the exact order of their con- 

 taining less quartz, and being therefore more easily fusible 

 — as granite with a large proportion of felspar, porphyry, 

 serpentine, mica-schist, and clay slate. f If we take these 



* The general reader will find an interesting account of M. Four- 

 net's theory in Jameson's Edinburgh Journal, No. 47, p. 3. 

 f Jameson's Edinburgh Journal, No. 47. 



