as illustrative of Geology. 7S 



densatlonof vapours. Amorphousand crystallinestructures might 

 proceed either immediately from the vapours by means of their 

 cooling, or after having first passed into the fluid stale : stalactitic 

 forms only in the latter way. We have shewn on a former oc- 

 casion (Specimen Crystallographiae Metallurgicse,) how the imi- 

 tative figures, the capillary, fiUform, and dendritic forms, which 

 occur in veins, and particularly in certain native metals, such 

 as gold, silver, and copper, have received a satisfactory explana- 

 tion from a product of the furnace, called hair-copper. 



Not only is a general analogy found to subsist between certain 

 productions of the furnace that have originated in vapours, and 

 the formation of many veins of ore, but there is sometimes such 

 a perfect similitude displayed, that we may be misled to confound 

 pieces ejected from the furnace with fragments of the veins of 

 ore. In confirmation of this statement, witness pieces found in 

 the melting-hearth, and on the ground-stones of extinguished 

 furnaces in the Upper Harz silver mines, which, in the mass 

 transformed by the heat, contain veins of regenerated lead-glance, 

 of from scarcely a measureable size to the thickness of several 

 inches, together with ramifications, intersections, displacements, 

 and other phenomena peculiar to veins of ore. 



The phenomena exhibited by the formation of vapours, as 

 observed among the products of the foundry, point out the 

 essential difference that exists between veins formed by subli- 

 mation, and vein-like fillings up of fissures by masses which 

 penetrated into them in a state of fusion. Metallic veins are of 

 a perfectly different kind from veins of granite, porphyry, green- 

 stone, and basalt. But even in regard to the structure of the 

 vein in the former kind, a consideration of the productions of 

 the foundry is indicative of a difference, which consists in this, 

 that vapours either withdrew into already existent spaces or 

 clefts, that had been perhaps more or less widened by their 

 operation, or they penetrated as a loose or soft mass. Va- 

 pours penetrate in great variety into crevices in the walls of 

 mines, or in the hearths of furnaces, and form, by condensation, 

 partly upfiUings, partly coatings, presenting themselves very 

 often in crystals. To this class belong the most famed crystal- 

 lizations of oxide of zinc from the iron blast-furnace, which arc 

 sometimes accompanied by cubes of chloride of potassium. To 



