HEAT 



VEINS. 



341 



erous age, and partly through new fissures. The ores occur along the dikes, 

 and also penetrate the limestones ; the ejection of the igneous rocks, andesyte 

 and rhyolyte^was accompanied by the upward passage of the ores; and the 

 ores became much changed to secondary kinds by the action of the vapors. 

 The latest eruptions of the region were of basalt. 



316. 



m 



White Porph yry 



Gray Porphyry 



Blue Livfiestone 



Vein- Ore 

 material 



Fig. 316, two Carbonate Hill sections, Leadville, showing cavities of ore in the inclined stratum of 

 limestone, a, limestone; 6, porphyry; c, ore. Fig. 317, section at Printer Boy Hill mine; letters same 

 signification. Emmons. — 



The abundance of chloride and bromide of silver in these western mines 

 makes it probable that sea water contributed to the ascending vapors, 

 and that salt (NaCl) supplied the chlorine. In the Cretaceous period, the 

 mountain region was mostly submerged. The ores are supposed to have 

 come from the igneous rocks. (Becker, Emmons.) This was probably true 

 to a large extent in some cases, according to the facts afforded by the Kewee- 

 naw copper region. The hot lavas carried much of the metallic material to 

 the surface, and as cooling commenced, the ores were condensed in, or gath- 



