CHEMISTRY OF THE KOCKS. 57 



ina. It is as if chances as variable as winds and storms had 

 regulated the production and mixture. There is every gradation 

 in the texture of granite, from the fine-grained blocks of the 

 quarry, to the coarse compacted breccia so common among 

 bowlders. It is as if the deeper beds had slowly cooled under 

 great compression and consequent immobility of the particles, 

 while the superficial layers had been worked up and closely con- 

 glomerated at the surface. There are specimens of granite com- 

 posed of massive angular crystals that seem as if they had been 

 thrown together and cemented. It is again as if they were the 

 congealed debris of some terrific hail-storm of quartz, mica, and 

 feldspar. 



After the greater part of the silicious minerals had been de- 

 posited, and the cooler exterior gases had thus been let down to a 

 nearer vicinity with the heavier vapors, we find that the metals 

 proper began gradually to condense and fall. Those which have 

 no active affinities for the other elements were deposited in their 

 native purity. Others took on the forms of oxides or sulphurets, 

 according to their first exposures or strongest attractions. Among 

 the first of these cloud-productions, the rock records tell us, were 

 the scanty rainfalls of gold and platinum, and the more plentiful 

 showers of silver and copper. Rivulets of native ores ran along 

 the hardening crust, filling the veins and crevices, or mingling 

 with the liquid quartz that was seaming the granite and gneiss. 



Then from clouds of condensing iron vapor that must have 

 burned and scintillated with indescribable magnificence, fell the 

 thick heavy storms of the black lodestone, the blood-red hema- 

 tite, or the dark yellow pyrites. Possibly storm-centers were 

 established, over which the cyclones were held concentrated and 

 often repeated, by force of intense magnetic attractions which 

 have left their traces in almost every iron-mine. 



Following these, at times and places, came on the great snow- 

 storms of the waxy flakes of zinc-blende and the pearly calamine, 

 the red oxide or the white carbonate of lead and the gray galena, 

 the beautiful crystals of the tin-stone, the gray plumes of anti- 

 mony, and all the tinted and varied forms of the less abundant 

 ores and alloys. Meanwhile through all the long ages of these 



