138 Elements of Mineralogy. 



35 of argill, 4 of pure calcareous Earth, and 

 12 of iron. Another fpecimen from the 

 Lipari I/lands afforded 69 of filex, 22 of 

 argill, and 9 of iron. This muft have been 

 expofed to a very ftrong heat, for they melt 

 very difficultly perje. 



The black Agate of Iceland, (Lapis oljidla- 

 MIIS, Piedra de Galmac_o) is of this fort, and 

 its principles and their proportions nearly the 

 fame. 



The harder fort of pitch ftones, already de- 

 fcribed, which give fire with fteel, belong to 

 this fpecies. 



Mr. SauJJure has ingenioufly imitated all 

 thefe fpecies of lava, by melting more or lefs 

 perfeftly the compound argillaceous fpecies 

 into which hornftone enters as the moft copi- 

 ous ingredient, and which he therefore calls 

 Hornrock) Roche de corne^ and which are al- 

 ready defcribed. Voyage dans les Alpes, p. 

 127. And hence he juftly conjedhires that 

 this ftone, marl, and the fchifti (Species 6, 7, 

 and 8 of the Argillaceous Genus i are 

 the principal materials of lava, Ibid-> 131, 

 132. 



SPECIES XXI, 



