148 ONTOLOGY. 



d. Fire-formation. 



VOLCANIC-ROCKS. 



690. Volcanoes are secondary combustions of masses 

 that have originated through the primary combustion, 

 and are therefore only of local occurrence. Such com- 

 bustible masses are without doubt bodies belonging to 

 the class of Inflammables, and thus carbons, sulphur, sul- 

 phuretted metals. Simply burning gases would throw 

 up on high the masses of earth, but not heat them to the 

 degree of fusion. 



691. By the heat of these combustions the masses of 

 earth have been fused, forming lavas. The silicious 

 lavas are obsidian, pitch-stone. The argillaceous lavas 

 are the kinds usually met with. Next come the talcose 

 lavas. The calcareous lavas are probably dolomite. 



B. METALLIC ORES AND INFLAMMABLES. 



692. Metallic -ores and Inflammables are products of 

 the planet, when completed, and have not originated 

 along with the origin of the latter, like the earths. The 

 question accordingly arises, what have been the forces by 

 which the metals and Inflammables were produced. 



a. METALLIC VEINS, 



693. Fissures in rocks, so narrow that they cannot be 

 illuminated by the sun, are called passages or veins. 

 They are rarely found in granite, appear generally for 

 the first time in gneiss, more rarely in the later kinds of 

 rocks, and almost cease to be met with in the stratified 

 chain of mountains. They are found principally in moun- 

 tains, and thus in masses of earth which project above 

 the level land. We must thus arrive at the conclusion 

 that they have there originated by actual fissure, and that 

 indeed for this reason, that masses which project or stand 

 freely out would admit of yielding asunder more easily 

 than the masses of the plains. This fissure may take 



