as illustrative of Geology. 69 



when the condensation very rapidly ensues, a loose powdery or 

 volatile aggregation, similar to what we observe in the sediment 

 of white arsenic in roasting ovens, or in the flowers of zinc that 

 are formed by sublimation. If we apply these experiments to a 

 more close investigation of the mineral bodies formed by the grand 

 sublimation process of the earth, we must certainly not overlook 

 the circumstance, that similar forms to those above mentioned 

 are frequently generated in the moist way, entirely without the 

 operation of fire, and that consequently, these forms can only 

 yield explanations as to the course of formation, when a general 

 conclusion has been come to respecting their nature. 



If the inquiry into the products of furnaces makes us ac- 

 quainted with a variety of bodies transformed by the heat of the 

 melting furnaces into vapour, we shall be induced to attribute to 

 the sublimation process of the earth a more extensive range o\ 

 action, than would have otherwise perhaps been our inclination. 

 We may conclude from the nature of the productions of the 

 foundry, that certain bodies, with whose existence in a state of 

 vapour we were either not at all, or with but little certainty ac- 

 quainted, passed from these states into solid ones. Now, if this 

 could take place with the heat of the melting furnaces, how much 

 greater is the possibility of the formation of vapours, by the 

 operation of the fire of the subterraneous forge of the globe. 



In the blast furnaces crude iron penetrates not unfrequently 

 into the fissures of the mass of which the building consists : a 

 phenomenon of little importance. But iron also is sometimes 

 found in the interior of a sandstone which has been exposed to 

 a high temperature, partly in veins, partly disseminated, with- 

 out the shghtest trace of any fissure, — so that this supposition 

 alone appears admissible, that it penetrated in a state of vapour 

 into the sandstone when softened by a high temperature. This 

 kind of iron is distinguished by a very light silver-white colour, 

 and has here and there externally a steel-grey tint, has a granular 

 foliated structure, and is so ductile that, when even in a cold state, 

 it may be hammered out into thin laminae. It contains sllicium 

 and carbon, and it is worthy of remark, that silica is sometimes 

 associated with the iron ; at all events, the appearance we have 

 described bears a striking resemblance to the manner in which 

 certain metals and ores, especially gold, silver, and copper, are 



