The first period was that of exchange with the natives, or of mere rapine. The second was distinguished by the conquest and plunder of Mexico, Peru and New Granada, and by the opening of the first mines. The third began with the discovery of the rich mines of Potosi; and in the course of it the conquest of Chili was completed, and various mines opened in Mexico. At the commencement of the fourth period, the mines of Potosi began to be exhausted; but those of Lauricocha were discovered, and the produce of Mexico rose from two millions to five millions of dollars annually. The fifth period began with the discovery of gold in Brazil; and the sixth was distinguished by the prodigious increase of the mines of Mexico, while those of every other part of America, with the exception of Brazil, were then constantly improving. The gold mines of Brazil have been very productive. Those called general, were about seventy-five leagues from Rio Janeiro, the staple and principal outlet of the riches of the Brazilian territory. They formerly yielded to the king, annually, for his right of fifths, at least one hundred and twelve arobas (weighing twenty-five pounds each) of gold; so that their yearly produce might then have been estimated at upward of three and a half millions of dollars, and that of the more distant mines at about one-third the sum. The gold drawn from them could not be carried to Rio Janeiro, without being first brought to the smelting-houses established in each district, where the right of the crown was received. What belonged to private persons was remitted in bars, with their weight, number, and an impression of the royal arms. The gold was then assayed, and its standard imprinted on each bar. When these bars were carried to the mint, their value was paid to the possessor in coin, commonly in half-doubloons, each worth eight Spanish dollars. Upon each of these half-doubloons the king gained a dollar, by the alloy and right of coinage. The mint of Rio Janeiro was one of the most beautiful in existence, and furnished with every convenience for working with the greatest celerity. As the gold came from the mines at the same time that the fleets came from Portugal, the operations of the mint and the coinage proceeded with surprising quickness.