THE COMSTOCK LODE. 53 



usual, are intersected by clay veins, and are of a semi-decomposed, spongy 

 nature. Tlie whole mass of the lode here, both quartz and horse, is impreg- 

 nated with iron pyrites, and near the surface all its cracks and faces are glazed 

 with coatings of oxide of manganese. 



Following the east wall, from the surface down 400 feet, is a body of ore 

 which widens from a thin seam to 80 feet on the 218-foot level, and then nar- 

 rows again to its lower termination. The greatest width of this is in the Potosi 

 adit, and here, in its very heart, is a zone of barren red quartz, included after 

 the manner of a horse. Below the 242-foot level the ore leaves the east wall, 

 and is separated from it by a thin plate of dead white quartz. From the same 

 level to the Chollar-Potosi first station, the white quartz gradually cuts out the 

 red; in other words, the action of surface oxidation descended lowest upon the 

 west wall, and gave out altogether at a depth of 400 feet. Below the junction 

 of the walls, at 669 feet below the datum-point, the vein is entirely wanting, 

 the propylite resting in almost exact contact with the syenite, the separating 

 sheet of clay being almost as thin as paper. Explorations have been pushed 

 downward to a depth of 1,408 feet below the datum-point without any signs 

 of the lode making again. 



The next section to the north, on Atlas-Plate 9, is through the Potosi 

 shaft. Here the same general features are observable. The vein begins to 

 branch upward at a somewhat deeper level, just below the 242-foot station, 

 and, in consequence, the two horses descend further into the lode. There 

 is also a greater expansion from east to west. The surface line following the 

 incline of the hill gives 750 feet of outcropping material; the longitudinal 

 width on the level of the Potosi adit is 400 feet; the vein also descends to a 

 greater depth, the contact of the two walls taking place half way between 

 the second and third Chollar-Potosi stations, or at a point 830 feet beneath the 

 datum-point. 



The ore, as in the former section, follows the eastern wall from the sur- 

 face down to about 500 feet; it is, however, narrower, never exceeding 50 

 feet. From the 350-foot level down to the first Chollar-Potosi station, the 

 quartz is separated from the west wall by a thin sheet of irruptive rock which, 

 from evidence hereafter adduced, is considered to be a dike of andesite. As 



