occupation in the Caribbean. Placer gold mining using forced indigenous labor did yield relatively small amounts of gold and did not have a huge deleterious environmental impact to the landscape, but the cost to the indigenous populations was considerable. Overwork contributed to their rapid demise. Starting the 1540s, silver became the major precious metal exploited by Spanish mining entrepreneurs under crown license. There were several mining sites in northern New Spain, particularly Guanajuato and Zacatecas, both outside the zone of dense indigenous settlement. In the highland Andes, there a single mountain, the Cerro Rico, in Potosí, Upper Peru (now Bolivia) was rich with veins of silver. In both Mexico and Peru, deep shaft mining required large numbers of laborers, but the footprint on the environment was not primarily caused by the mines themselves. Processing the pure silver from silver ore required considerable environmental costs. Around mining sites, there was massive deforestation, since early processing was by heating ore separating out molten silver. The early silver boom ended, in good part because the fuel to process the ore was exhausted through deforestation. In both Mexico and Peru, the introduction of mercury amalgam to process ore resulted in the revival of mining and more insidious and long-term environmental impacts. Mercury mined in Almadén, Spain and shipped to Mexico in leather bags and transported to mining sites by mule. Like silver, mercury was a crown monopoly, so that the crown expected to reap maximum wealth from this resource. Costs of mining, transatlantic transportation, and the overland transport added to the costs to mining entrepreneurs. High costs for mercury often resulted in the abandonment of mining sites, since it had an impact on profitability. In the eighteenth century, the Spanish crown calculated that lowering the cost of mercury to miners in Mexico would result in higher silver output. The respite of the environment of Northern Mexico from mercury poisoning ended and the eighteenth century saw a boom in silver production. In Peru, there was a local source of mercury, the Huancavelica mine, making production costs cheaper, but with a far higher cost to the human and natural environment in the region. The toxicity of mercury was known at the time, although the science of it was not. When mercury was discovered in significant amounts at Huancavelica, Peru's silver mining industry could regain its previous levels of output. Forced indigenous labor was directed toward mining