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130 teaching American methods and the use of American mining machinery to the native Mexicans, thereby increasing their value to their families and to their country.

El Oro, State of Mexico. In recent years, this camp has been the most important producer of gold in Mexico. It was not worked by the Spaniards or Mexicans who overlooked it because the ores did not out-crop on the surface. The professional knowledge of mining engineers was required to reveal the existence of the ore under the surface. The large mines were developed by British and French capital, the former being expended under the direction of American mining engineers, who also built the railway connecting the camp with the outside world. Before the revolution, this camp gave employment to about 7,000 men. The ores were treated by the cyanide process introduced by Americans.

San Pedro, State of San Luis Potosi. The vast gold deposits of this camp were discovered by the Spaniards and since that event mining activity has never ceased. Due to the fact that the mines were dry and the ores were amenable to smelting in primitive adobe furnaces, Spanish methods were unusually successful and resulted in the production of gold by them to the amount of some hundreds of