326 RESOURCES OF CALIFORNIA. 



stone, which sometimes, but rarely, pays for the work of taking 

 it out. After the shaft or incline is down, levels or drifts are 

 run off horizontally as far as the pay-rock extends, at intervals 

 usually of a hundred feet, and the levels are numbered from 

 the surface ; so when we read that they have found good rock 

 in a certain mine at the eighth level, we presume that it is 

 eight hundred feet below the surface. The rock between two 

 levels is broken down or stoped out. and it falls to the drift or 

 level below, where it is loaded in a car and hauled to the 

 shaft, in which it is carried up. 



248. Pulverization. Nearly all the quartz of California 

 is crushed by stamps or iron hammers, ten inches in diameter, 

 and weighing 500 pounds. The stamp is fastened to a vertical 

 iron stem about six feet long, and near the top is a projection 

 by which a cam or a revolving shaft lifts the stamp a foot 

 high and then lets it fall. Five stamps are placed side by side 

 in a battery, and they fall successively, each making about 40 

 blows in a minute. The quartz is shoveled in on the upper 

 side, and when pulverized sufficiently, it is carried away 

 through a wire screen on the lower side by a stream of water, 

 which pours into the battery steadily. 



249 Arrastra. The arrastra is the simplest instrument 

 for grinding auriferous quartz. It is a circular bed of stone, 

 from eight to twenty feet in diameter, on which the quartz is 

 ground by a large stone dragged round and round by horse 

 or mule power. There are two kinds of arrastras, the rude 

 and improved. The rude arrastra is made with a pavement of 

 unhewn flat stones, which are usually laid down in clay. The 

 pavement of the improved arrastra is made of hewn stone, 

 cut very accurately and laid down in cement. In the center 

 of the bed of the arrastra is an upright post which turns on a 

 pivot, and running through the post is a horizontal bar, pro- 

 jecting on each side to the outer edge of the pavement. On 

 each arm of this bar is attached by a chain a large flat stone 

 or muller, weighing from three hundred to five hundred 



